Integrated General Biology A Contextualized Approach
Active Learning Activities
Student Version FIRST EDITION
Jason E. Banks
Julianna L. Johns
Diane K. Vorbroker, PhD
Molecules, Compounds, & Chemical Bonds Active Learning Activities
Let's Bond, Chemically 2
Chapter 3 Molecules, Compounds, & Chemical Bonds
Section 3.1 Let's Bond, Chemically Directions for the Student:
This lesson is designed for you to complete, on your own or in your study group. Use your notes and follow along in the text, as you find necessary.
Objectives: 1. Define a chemical bond. 2. Describe trends in the chemical behavior of metals and non-metals. 3. Describe ionic bonds and predict the chemical formula for ionic bonds. 4. Differentiate between a cation and an anion. 5. Identify groups of atoms as a compound and/or a molecule.
Chemical reactions involve the movement and the changes in the arrangement of the electrons. While
the nucleus of the atom must also be understood, we will be focusing on the electrons and their
positions. Therefore, instead of drawing each nucleon, only the chemical symbol for the atom or ion
will be drawn to represent the nucleus. Sometimes all of the electrons will be drawn, and sometimes
only the valence electrons will be drawn. You must be comfortable with all of the different notations
and be able to move freely between them.
1. Look at the diagram of sodium and chlorine. Remembering that the most stable arrangement of electrons is a complete outermost shell, predict what will happen when a sodium atom meets a chlorine atom.
Sodium has one electron in its outer shell. Chlorine has seven electrons in its outer shell. When they react sodium loses an electron to become a sodium ion with a charge of +1. Chlorine atoms accept an electron to become chloride ions with a charge of -1. After reacting the sodium and chloride ions have a full outer shell of electrons. A full outer shell of electrons is a stable arrangement.
Sodium and chlorine bond together to form table salt. There are many other salts, but sodium chloride is
the most famous (notice that we change the ending on the non-metal to “-ide” when it forms an ion).
If sodium loses its outermost electron, its new outermost shell will be complete (the 2nd orbital). And, if
chlorine gains the electron from sodium, chlorine will also have a complete outermost shell with 8
electrons in its 3rd orbital.
2. What type of element (metal, nonmetal or metalloid) is Sodium? metal
3. What type of element (metal, nonmetal or metalloid) is Chlorine? nonmetal
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Atoms can be seen as the building blocks for life. Atoms link together to form larger molecules and build
the structures that make up everything we can see, touch, taste or smell. But what happens when atoms
bond together?
There are many different types of bonds, but we will focus here on ionic bonds.
As the name implies, ions are formed when two atoms form an ionic bond.
4. What are the two different types of ions? Use the examples from the first question.
An ion is an atom or group of atoms in which the number of electrons is not equal to the number of protons, giving it a net positive or negative electrical charge. An anion is an ion that is negatively charged, and is attracted to the anode (positive electrode) in electrolysis. A cation has a net positive charge, and is attracted to the cathode (negative electrode) during electrolysis. In the first question, Na is considered to be the cation as it loses an electron and its overall charge becomes positive. Therefore, Cl is considered to be the anion because it gains an electron and its overall charge becomes negative.
Some atoms lose electrons and some atoms gain electrons to form a complete outermost shell (valence
orbital). Metals tend to lose electrons and nonmetals tend to gain electrons. This means that metals and
nonmetals will form ionic bonds when they meet. In ionic bonds, the electron is transferred from the
metal to the nonmetal. This means that the electron is no longer counted for the metal, and is now part
of the nonmetal. Now that a charged particle has been transferred, the charge on the atom has now
changed, and it is now a charged atom, or ion. This ion now has a complete outermost shell, and is an
example of the Octet Rule (or Duet rule if there is only one orbital).
5. The chemical symbol for magnesium is drawn (as the nucleus). Using question number 1 as a guide, add all of magnesium’s electrons (in its atomic state, not its ionic state). Use the periodic table to help you remember how many electrons can fit into each orbital (by counting the number of spaces in each row until you get to the element you are drawing).
Mg
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6. Draw sulfur (with its chemical symbol as the nucleus) and all of its electrons in the atomic state.
7. Complete the table.
8. Draw the electron dot diagram for each element from the table. Then draw an arrow from the
metal’s electron(s) to the nonmetal’s open space(s) representing a transfer of the electron(s) and
the formation of ions. Name the newly formed compound with the metal first and the nonmetal
second, and change the ending of the nonmetal to “-ide”. Also, give the chemical formula for the
compound (count how many of each element there are and write it as a subscript, even if it is a “1”
for now).
Name Formula Diagram
Sodium Chloride Na1Cl1
Element Type # of
Protons
# of Valence
Electrons How it forms an
Ion
New # of Electrons (total) as
an ion Ionic Charge (p
– e)
Sodium metal 11 1 Loses 1 electron 10 11 – 10 = 1+
Chlorine nonmetal 17 7 Gains 1 electron 18 17 – 18 = 1-
Magnesium metal 12 2 Loses 2 electrons 10 12 – 10 = 2+
Sulfur nonmetal 16 6 Gains 2 electrons 18 16 – 18 = 2-
Aluminum metal 13 3 Loses 3 electrons 10 13 – 10 = 3+
Nitrogen nonmetal 7 5 Gains 3 electrons 10 7 – 10 = 3-
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Magnesium Sulfide Mg1S1
Aluminum Nitride Al1N1
Notice how each of the parts of problem number 7 are perfectly matched . . . sodium needed to lose
one electron while chlorine need to gain one electron, and magnesium needed to lose two electrons
while sulfur needed to gain two electrons, and so on.
Since these particular elements are matched so well, only one atom of each element was required to
form a complete valence shell. This is not always the case, and additional atoms of either element may
need to be added to form a stable compound (group of at least two different elements bonded
together, like when sodium and chlorine bond together).
9. Draw the electron dot diagrams for the elements and add additional atoms as necessary to empty
the valence shell of the metal and complete the valence shell of the nonmetal. Draw arrows showing
where the electrons will go. Then name the compound you formed.
Name Formula Diagram
Magnesium Chloride
Mg1Cl2
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Aluminum Bromide
Al1Br3
Sodium Oxide
Na2O
Sodium Phosphide
Na3P
Adding more atoms of the same elements makes sense because they are already there in the reaction—
we just haven’t drawn all of them. Think of it this way: it would be extremely difficult to get only two
atoms together, but almost anyone could add many magnesium atoms to many chlorine atoms. There
are extra magnesium and chlorine atoms all around the two that happened to be drawn.
In some cases, it may be necessary to add more atoms of both elements. Every electron from the metal
must be moved and every space in the valence shell of the nonmetal must be filled.
10. Draw the electron dot diagrams for the following elements. Add more atoms of each element as
necessary. Name the ionic compound and give its chemical formula.
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Name Formula Diagram
Magnesium Nitride
Mg3N2
Only add one atom at a time, as necessary, until finished
Calcium Nitride
Ca3N2
Aluminum Sulfide
Al2S3
Understanding the previous problems is very important—you must be able to trace the electrons as
they leave the metal and go to the non-metal in the formation of these ionic bonds. However, there is a
faster method of determining the formula for ionic compounds.
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When we write the ionic charges next to the formulas, an interesting pattern appears.
11. Complete the table. Chemists don’t usually write “1”s, but we will write them here. Also, be sure to
write the charges as superscripts and how many there are (quantity) as subscripts.
12. Write an EVIDENCE and a CLAIM (based on the evidence) from the table above.
Evidence Claim
Any example from above
Total (+) charge must equal total (-) charge
Number of electrons lost MUST EQUAL number of electrons gained
Symbol of cation always written FIRST
Symbol of anion always written SECOND
Use CRISS-CROSS method short-cut
method to determine correct formula
Remember to simplify subscripts!
The pattern of dropping the signs from the charges and switching the numbers to give you the formula
could be called the SWITCHEROO Pattern. The following shows how we can apply this pattern to
aluminum sulfide:
Step 1: Find the Ionic Charges Al3+ S2-
Metal Nonmetal Ionic Charge on
the Metal Ionic Charge on the Nonmetal Chemical Formula
Sodium Chlorine Na1+ Cl1- Na1Cl1
Magnesium Bromine Mg2+ Br1- Mg1Br2
Iron (III) Oxygen Fe3+ O2- Fe2O3
Copper (II) Nitrogen Cu2+ N3- Cu3N2
Aluminum Iodine Al3+ I1- Al1I3
Magnesium Nitrogen Mg2+ N3- Mg3N2
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Step 2: Drop the signs and switch the numbers to make the subscripts Al2S3
You now know two ways of predicting the formula for ionic compounds: the first method is to draw the
valence electrons with arrows showing how they move from the metal to the nonmetal, and the second
method is to switch the numbers (without the signs) of the ionic charges. But, there is something you
must be careful about when using this new pattern.
13. Find the chemical formula for magnesium oxide. Use both methods that we have learned.
Method 1: Draw the electron dot diagram for each element and show (using arrows) where the
electrons will transfer to, then predict the chemical formula.
Name Chemical Formula Diagram
Magnesium Oxide MgO
Method 2: Find the ionic charges for each element, and switch the numbers (without the signs).
Step 1: Find the Ionic Charges Mg2+ O2-
Step 2: Drop the signs and switch the numbers to make the subscripts
Mg2O2 –> MgO
Were the answers the same? Which one is correct?
There is never any need for any adjustments to be made when using Method 1. However, if the ionic
charges have the same (absolute) value, they can be cancelled to one. The correct formula for
magnesium oxide is Mg1O1 (although chemists don’t write the “1”s).
But what happens when the charges have a common factor?
14. Find the chemical formula for manganese (IV) oxide. Use both methods we have learned.
Method 1: Draw the electron dot diagram for each element and show (using arrows) where the
electrons will transfer to, then predict the chemical formula.
Name Chemical Formula Diagram
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Manganese Oxide MnO2
Method 2: Find the ionic charges for each element, and switch the numbers (without the signs).
Step 1: Find the Ionic Charges Mn4+ O2-
Step 2: Drop the signs and switch the numbers to make the subscripts
Mn2O4 MnO2
Which answer is correct? When using the SWITCHEROO method and there is a common factor in the
ionic charges, you must simplify the ratio. The chemical formula for manganese (IV) oxide is Mn1O2.
Whatever method you choose to use, remember that ionic bonds represent a transfer of electrons from
the metal to the nonmetal. This complete transfer results in the formation of a positive cation (the
metal) and a negative anion (the nonmetal).
Ionic bonds are a result of large differences in the electronegativity of the two elements . . . in other
words, the nonmetal (with a high electronegativity) pulls electrons much more than the metal (with a
low electronegativity).
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Bond, Covalent Bond 11
Section 3.2 Bond, Covalent Bond Directions for the Student:
This lesson is designed for you to complete, on your own or in your study group. Use your notes and follow along in the text, as you find necessary.
Objectives: 1. Describe how covalent bonds are formed. 2. Differentiate between a polar covalent bond and a non-polar covalent bond.
Describe some effects of each type of bond. 3. Predict the type of bond formed between two elements when given the elements'
electronegativities. 4. Predict the chemical formula for molecules forming covalent bonds. Name the
molecule formed. 5. Differentiate between single, double and triple covalent bonds. 6. Use electron dot diagrams to explain how the valence electrons are arranged in
covalent bonds. 7. Draw stick diagrams to represent covalent bonds.
Nonmetals are found in the upper right-hand corner of the periodic table. From our study of ionic
bonds, we know how many times each nonmetal can bond—it will bond until it has a complete
outermost shell.
1. Complete the table by predicting the number of times these common nonmetals can bond.
If ionic bonds transfer electrons from one element (the metal) to another (the nonmetal), what will
happen when two nonmetals bond? Nonmetals have a high electronegativity (they pull electrons with a
large force).
2. Predict what will happen if two nonmetals bond.
Instead of transferring electrons like in ionic bonds, there will now be a sharing of the electrons forming a covalent bond
Element Valence Number
Number of additional electrons required to complete
valence shell Number of times element
can bond
Carbon 4 4 4
Nitrogen 5 3 3
Oxygen 6 2 2
Fluorine 7 1 1
Sulfur 6 2 2
Chlorine 7 1 1
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When two nonmetals bond, they share a pair electrons in a covalent bond. A covalent bond is
significantly stronger than an ionic bond. As a result, covalent bonds do not break apart (disassociate) in
water (aqueous environments).
Sometimes, nonmetals bond with themselves. This example serves as a good introduction to covalent
bonds. While it is still important to be able to draw the nucleus and all of the electrons, we will only
focus on the valence electrons, as that is where the electrons are that form chemical bonds.
3. Draw the electron dot diagram (just the valence electrons) for chlorine. Since there are two
chlorine atoms, draw the first electron dot diagram using small dots (like normal) and draw the
second electron dot diagram using small “x”s. (It is recommended that you place the one spot
without an electron in between the two atoms.)
Cl Cl
Next, without adding anymore electrons, find a way to make the valence shells complete on BOTH
fluorine atoms.
F F
Finally, around each atom draw a circle that is just outside all of the electrons that count for that
atom. Does each atom meet the requirements for the Octet Rule?
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By sharing electrons, a covalent bond can make it seem as though there are more electrons than there
really are. Each atom requires 8 valence electrons in its outermost shell to be stable (the Octet Rule),
which means there should be a total of 16 valence electrons drawn, right? But by sharing a PAIR OF
ELECTRONS, a covalent bond can make 14 valence electrons seem like 16 valence electrons.
This is an example of a diatomic (di- means two) molecule that is also homonuclear (homo- means
same), which means the two atoms that are joined are of the same element.
There are seven elements that form homonuclear diatomic molecules:
hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine and iodine. Since
chlorine and fluorine are in the same column, the electron dot diagram
for F2 will be identical to that of Cl2 (with the exception of the chemical
symbols, of course).
When two atoms share a pair of electrons, forming a covalent bond, we
often draw a stick to represent that pair of shared electrons.
4. Draw a covalent bond, represented only by a stick, between two fluorine atoms.
F F
This is how chemists represent a SINGLE BOND. This is called a single bond, but it is a PAIR of electrons
(one electron from one atom, and another electron from the other atom).
Again, since chlorine and fluorine are in the same column and have the same
number of valence electrons, the diagram for chlorine would look like just like
that of fluorine.
Single bonds are very common, but there are also double and triple covalent bonds.
5. Understanding how bonds are created and how to describe them are an important part of
Chemistry. Answer the following questions about bonds.
If a single bond is between two atoms that share one pair of electrons, predict how many pairs of electrons will be shared in a double bond and in a triple bond.
Two, three
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A single bond is between two atoms that share a pair of electrons. A double bond is between two atoms that share how many electrons?
two
A triple bond is between two atoms that share how many electrons?
three
When an oxygen atom forms a diatomic molecule with another oxygen atom (a homonuclear diatomic
molecule), two pairs of electrons are shared, forming a double bond. The electron dot diagram below is
already completed on the first oxygen atom.
6. Complete the electron dot diagram for the other oxygen atom, showing how there are two pairs of electrons between the two oxygen atoms. (It is recommended that you draw the electrons around the second oxygen in a mirror image to the one already completed.) Then, for each atom, draw a circle around the electrons that are counted for that atom, and satisfy the Octet Rule for each.
7. If a single bond is represented by one stick, predict what a double bond will be represented by.
two sticks
8. Draw a double bond between two oxygen atoms with sticks (and their chemical symbols).
The greatest number of bonds that two nonmetals can share between them is 3. A triple bond shares 3
pairs of electrons, and occurs in the diatomic homonuclear molecule N2. Metallic bonds formed by two
transition metals may form a quadruple bond, but two nonmetals will not. Do not confuse a quadruple
bond with an atom bonding four times. For example, carbon will bond four times, but not all four bonds
will be formed with one other atom.
9. When a nitrogen atom forms a diatomic molecule with another oxygen atom (a homonuclear
diatomic molecule), three pairs of electrons are shared, forming a triple bond. The electron dot
diagram is already completed on the first nitrogen atom. Complete the electron dot diagram for
the other nitrogen atom, showing how there are two pairs of electrons between the two nitrogen
atoms. (It is recommended that you draw the electrons around the second nitrogen in a mirror
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image to the one already completed.) Then, for each atom, draw a circle around the electrons
that are counted for that atom, making sure to satisfy the Octet Rule for each.
10. Draw a triple bond between two nitrogen atoms with sticks (and their chemical symbols).
The molecules that we have studied so far are made of the same element. This means that they both
pull the electrons with the same force . . . there is no difference in their electronegativities. This means
that the atoms involved share their electrons very evenly with each other, and will not become charged.
Covalent bonds that are comprised of elements with similar or the same electronegativities and,
therefore, pull the electrons very evenly, share the electrons evenly and are called nonpolar covalent
bonds.
In ionic bonds, the electron was transferred from the metal to the nonmetal, forming charged atoms, or
ions. Nonpolar covalent bonds involve a more equal sharing of the electrons, so neither atom will
become charged. They are called “nonpolar” because the atoms do not have slightly different charge . . .
there are no poles of opposite charges on the ends of the molecules.
But this is not always the case. Sometimes, two atoms will only partially share their electrons.
11. Hydrogen has a somewhat strong pull on electrons, but it is not nearly as strong as oxygen’s pull on electrons. Oxygen will pull electrons to its outermost shell with a stronger force than hydrogen. Predict what will happen to the valence electrons if two hydrogen atoms bond with an oxygen atom.
Because the oxygen atom is larger than the hydrogen atom, its attraction for the hydrogen's electrons is correspondingly greater so the electrons are drawn closer in to the orbit of the larger oxygen atom and away from the hydrogen orbits.
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Since hydrogen does not pull an electron as much as oxygen, the
electrons will spend more time near the oxygen atom. This is not a
complete transfer of the electrons, so the oxygen does not get a
FULL additional negative charge from the extra electrons. Instead,
the oxygen just get a partial negative charge and the hydrogen gets
a partial positive charge. This partial charge is designated with a “δ”, the lower case Greek symbol for
delta.
This molecule has partial charges on it, with opposite poles. The oxygen end has a slight negative charge,
and the hydrogen end has a slight positive charge. As such, molecules that do not share electrons
evenly are called polar covalent bonds because they have different poles (or ends) with opposite
charges.
Notice that when you draw the circles around the atoms to show which electrons count for each atom,
you will only circle two electrons for hydrogen.
12. Why is hydrogen stable with only two electrons in its outermost shell?
For stability, an atom tries to reach the electronic configuration (arrangement of electrons in orbits) of the nearest noble gas. The noble gas nearest to Hydrogen is Helium. So, it gains 1 electron to get Helium's configuration which is 2 electrons.
13. Draw H2O (water) using a stick model. Use the electron dot diagram of water as a guide. Add the partial charges where necessary.
Generally speaking, metals bonding with nonmetals will form ionic bonds and nonmetals bonding with
nonmetals will form covalent bonds. However, that is only a generalization. To be certain what type of
bond is formed, one should always check the difference in the electronegativities.
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Electronegativity for Bonding Elements
Note: These numbers may vary, depending on which scale you use and which sources you reference, but
the trends remain the same. (Note: These ranges may slightly vary, depending on which source you
reference.)
Difference in Electronegativity Type of Bond
0.0 – 0.3 Nonpolar Covalent
0.4 – 1.7 Polar Covalent
1.8 – 3.3 Ionic
14. Using the table with the electronegativities, what happens to the electronegativity value as you move up a column?
It increases
15. What happens to the electronegativity value as you move right, across a row?
It increases
16. Determine what type of bond is formed when these two elements bond. Write the larger of the two
electronegativities first when subtracting to avoid a negative value.
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17. Draw NH3 (ammonia) using an electron dot molecule. Circle the electrons that count for each atom. (Hint: Draw nitrogen with a pair of electrons on one side and only one electron on the other three sides.)
18. Draw a stick model for NH3 and determine what type of bond is formed. If necessary, put partial charges in the proper places.
19. Draw CO2 using an electron dot diagram and stick model. Remember that, in order to have a stable electron arrangement, carbon must bond 4 times and each oxygen must bond 2 times. (Hint: Start by drawing carbon in the middle of the oxygen atoms, and put a pair of electrons on carbon’s right and left.)
Element 1 Element 1
Electronegativity Element 2 Element 2
Electronegativity Difference in
Electronegativity Type of
bond
Sodium 0.9 Chlorine 3.0 3.0 – 0.9 = 2.1 ionic
Hydrogen 2.1 Carbon 2.5 2.5 – 2.1 = 0.4 Polar Covalent
Chlorine 3.0 Bromine 2.8 3.0 – 2.8 = 0.2 Covalent
Hydrogen 2.1 Oxygen 3.5 3.5 – 2.1 = 1.4 Polar Covalent
Fluorine 4.0 Fluorine 4.0 4.0 – 4.0 = 0 Non-Polar Covalent
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Functional Groups 19
Section 3.3 Functional Groups Directions for the Student:
This lesson is designed for you to complete, on your own or in your study group. Use your notes and follow along in the text, as you find necessary.
Objectives: 1. Differentiate between a functional group, a free radical and a polyatomic ion. 2. Identify and describe the significance of six biologically important functional groups
(hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, and phosphate).
Organic molecules are carbon-based. This means that they often have long backbones of carbon,
forming molecules that are long chains. But not all of the atoms along this long chain are reactive. In
fact, the molecule may be very stable, with only one area that is reactive. This area is called a functional
group, and it determines how the molecule will behave chemically (react and bond).
A functional group is different from a polyatomic ion or a radical. See if you can tell how.
1. Complete the table.
Notes Drawings Questions
Hydroxide Ion—
I notice that…
Hydroxyl Radical—
I notice that…
Hydroxy Group—
I notice that…
1. Which one has a charge?
2. Which one is part of a larger molecule and is attached to more atoms?
3. Which one has an unpaired valence electron that makes it very reactive?
Ions are atoms or groups of atoms that have gained or lost an electron. This means that there are no
longer equal numbers of charged particles (positive protons and negative electrons), so there is an
overall charge. Groups of two or more atoms bonded together that have an overall charge are called
polyatomic ions—these usually act as one unit as they react, with the charge being spread over the
entire polyatomic ion.
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Free radicals (often referred to as simply “radicals”) have an unpaired valence electron. This means that
the atom does not have a stable electron arrangement, and is not following the Octet rule. In the
hydroxyl radical, the unpaired valence electron on oxygen means that oxygen only has seven electrons
in its outermost shell. When this oxygen is given a chance to react and gain that last electron that it
needs to become stable, it will do so—this makes it very reactive.
Functional groups are groups of atoms within a larger molecule that are more reactive than other areas
of the molecule, and determine how the overall molecule will react. There are six important functional
groups in Biology that greatly affect living organisms. These functional groups determine the chemical
behavior of the molecules that are the basis for life as we know it.
The hydroxy group (often referred to as the hydroxyl group) shows that it is part of a larger molecule
with a large stick off the side of the oxygen atom. This functional group plays a large role in determining
how the entire molecule will behave.
2. Examine the molecule below. There are usually so many carbon atoms in biomolecules (organic
molecules are carbon-based) that chemists don’t like to write the “C”s. Instead, we have to remember
that there is a carbon wherever two lines (bonds) meet.
Identify all of the hydroxyl groups by marking each one.
Notice that this molecule has three phosphate groups, a 5-carbon sugar (ribose) and a nitrogenous base
(adenine). This molecule is often called the energy currency of the cell.
3. What is the molecule pictured in #2? Adenosine Triphosphate (ATP)
Hydroxyl functional groups play a very important role in dehydration synthesis, which forms larger
molecules from smaller molecules by removing a water molecule.
Monosaccharide—OH + H—Monosaccharide Disaccharide + H2O
4. Explain the role of the hydroxy group in dehydration synthesis.
The hydroxy group can combine with a hydrogen atom from the other molecule to form water, leaving an unbounded atom on each molecule, allowing them to bond.
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Functional groups are more reactive than other areas of the larger molecule. Oxygen is more
electronegative (pulls the electrons more) than hydrogen, making partial charges on each atom and
increasing its reactivity. This means that the electrons that are “shared” in the covalent bonds are held a
little more closely to the oxygen atom than to the hydrogen atom (making a “polar” covalent bond with
ends that have opposite partial charges).
Another important functional group is the carbonyl group. This group is simply a carbon that has a
double bond with an oxygen atom. Oxygen is very electronegative, and it pulls the electrons with more
force than the carbon atom.
5. Identify carbonyl group in the molecule with a mark over the top of the molecule where the carbonyl group is. How many carbonyl groups are there in this molecule?
There is only one carbonyl group in this molecule.
6. Identify a similarity and some differences between these molecules:
Remember that “R” simply stands for the Rest of the molecule (a side group), which could be many atoms or simply just one atom. R’ means that it leads to another set of atoms and is said as “R prime” (you may have two or more “Rests” of the molecules).
Both molecules have a carbonyl group coming off of the central carbon. The molecule on the left only has one R-group while the molecule on the right has two R-groups.
Students will learn that the molecule on the left is an aldehyde and the molecule on the right is a ketone later.
While both of the molecules from #6 have a carbonyl group, the molecule on the left only has one R-
group while the molecule on the right. An aldehyde is a carbonyl functional group that has at least one
hydrogen attached to it (with only one side group), while a ketone is a carbonyl functional group that
has two side groups attached to it
Formaldehyde (simplest of the aldehydes) Acetone (used for cleaning in the laboratory)
It is possible to have more than one functional group on the same molecule. In fact, some functional
groups combine to form a larger, and differently named, functional group all together.
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7. Examine the molecule. What functional groups can you identify?
This molecule has a hydroxyl functional group and a carbonyl functional group.
Sometimes two functional groups can combine to make a new functional group. When both a hydroxyl
functional group and a carbonyl functional group are found together, they are called a carboxyl group.
Even the name “carboxyl” is a combination of the two smaller functional groups.
Because this group can donate a proton (a hydrogen ion, or H+), it is an acid. An organic compound with
a carboxyl group on it is referred to as a carboxylic acid. There are many different groups of atoms that
can on the “R” group of this molecule, which means there are many carboxylic acids. This group is
usually written as “-COOH” (with the stick showing that it is bonded with other atoms).
8. Carbonic acid is pictured below. It plays a very important role in our blood by keeping the acid-base system balanced (in homeostasis) and transports CO2
out of the blood stream. What functional group does carbonic acid have on it?
Carbonic acid has a carboxyl group on it.
9. Carbonic acid is also called “acid of the air” because it can result from carbon dioxide dissolving in water (making the water more acidic). Write an equation that shows water and carbon dioxide combing to form carbonic acid. Use double arrows (⇌) to show it can go back and forth to find an equilibrium (or balance).
CO2 + H2O ⇌ H2CO3
Students may also write carbonic acid as HOCOOH since it was stated that the carboxyl group is written as -COOH.
Without this system, we would not be able to remove carbon dioxide from our blood stream, and it is
also why the oceans can absorb so much carbon dioxide from the air (which makes the oceans more
acidic).
So far, we have only seen functional groups that use carbon, oxygen and hydrogen. But the next
functional group uses nitrogen.
Amine functional groups have a central nitrogen atom. While ammonia (pictured below) is not an amine
because the nitrogen is not bonded to any carbon atoms, it useful as a starting point to think of amines.
Molecules, Compounds, & Chemical Bonds Active Learning Activities
Functional Groups 23
The amine functional group has a nitrogen atom that is bonded three times (at least once to carbon) and
has a lone pair of electrons, which repel the bonds away, affecting the overall shape of the molecule.
(Do not confuse a “lone pair of electrons” with an unpaired valence electron—like on a free radical—
that is very reactive.)
When one of the three hydrogen atoms of ammonia is removed and replaced with a carbon compound
(represented by an “R” group), a primary amine arises. A secondary amine is bonded to two carbon
atoms. The nitrogen in a tertiary amine has all three of its bonds with a carbon compound.
10. Examine the molecule. What kind of amine is it? How do you know?
This is a secondary amine because it has two carbon compounds bound to the nitrogen.
11. Examine the molecule. What kind of amine is it? How do you know?
This is a primary amine because it only has one carbon compound bound to the nitrogen.
With these distinctions in mind, the most common way to refer to a nitrogen with two hydrogens
bonded to it is by calling it an amino group (which would be a primary amine when bonded with a
carbon compound). These play an important role in the structure of DNA, forming part of the
nitrogenous bases (adenine, guanine, cytosine and thymine).
12. Here is cytosine, a nitrogenous base on DNA. What functional group is on position 4?
The functional group at position 4 is an amino group.
Amino groups are found in many places, but none probably more important than amino acids, the
building blocks of proteins. (Take a moment to give the proper worth to proteins that they are due—
proteins, after all, make the vast majority of your body’s structures.)
In another combination of functional groups, an amino group and a carboxyl group (bonded around a
central carbon with an R group) together form an amino acid. Amino acids then bond with other amino
acids using peptide bonds, forming into polypeptides and proteins.
Molecules, Compounds, & Chemical Bonds Active Learning Activities
Functional Groups 24
13. Here is a basic structure on an amino acid. What parts of the amino acid are the same on all amino acids and what part differs on different amino acids?
The amino group, the central carbon, and the carboxyl group are common to all amino acids. The R group varies from amino acid to amino acid and determines what amino acid it is.
14. What functional group on “Amino acid 1” detaches to allow for the formation of the peptide bond with “Amino acid 2”? (Choose the smaller functional group, not the carboxyl group.)
The functional group on “Amino acid 1” that detaches to allow for the formation of the peptide bond is the hydroxyl functional group, which is part of the carboxyl functional group.
15. This reaction links together two molecules to create a larger molecule. What is the other product of this reaction?
Water (H2O) is the other product of this reaction.
16. This is called a condensation reaction, but can also be referred to by a different name. What is this type of reaction called that forms a new substance by combing two smaller molecules while removing water? (When naming this reaction, think about what you are if you don’t have enough water in your body.)
This type of reaction can be called a dehydration synthesis reaction.
Proteins are polymers, which means they have repeating subunits, like trains have cars. Proteins have
repeating amino acids, which means that amino acids are the monomers for proteins. By releasing the
hydroxyl group from one amino acid and a hydrogen atom on the amino group from the other amino
acid, this dehydration synthesis reaction forms a new compound while releasing water. This is one of the
most important reactions in all of biology, helping to form proteins and other biological polymers.
Molecules, Compounds, & Chemical Bonds Active Learning Activities
Functional Groups 25
The order of amino acids determines how the protein will behave chemically. But the bonds that link the
amino acids are not the only important bonds. These polypeptide chains that form during dehydration
synthesis are often very long—so long that they curl back on themselves and form additional bonds that
also determine chemical behavior.
17. Examine this polypeptide chain. What element is joining parts of the chain with other parts?
The polypeptide chain is joined with sulfur atoms to other parts of the chain.
The molecule pictured above is cysteine, which is an amino acid. Notice that it has the two usual
functional groups that all amino acids have. (If you do not know what these are, please go back and
review at this time.)
However, cysteine also has a sulfur atom bonded to a hydrogen atom as part of its “R” group (or side
chain). The sulfur and hydrogen atoms form a functional group called a thiol group, or a sulfhydryl
group. The thiol group is similar to a hydroxyl group, except that oxygen is replaced with sulfur.
18. Examine the amino acid cysteine. What functional groups can you find on it? Which ones are found on all amino acids?
The functional groups found on cysteine are the carboxyl group (which is made of a hydroxyl group and a carbonyl group), an amino group, and a thiol group. The carboxyl group and the amino group are found on all amino acids, but the thiol group is specific to cysteine.
When the amino acid cysteine is used in a polypeptide chain (protein), the thiol groups link up with
other thiol groups to form a disulfide bond. This bends and molds the protein into a specific shape
which allows it to perform specific jobs around the cell.
The disulfide bond, which is also called an SS-bond, is usually written as R-S-S-R’ showing the two R
groups off to either side of the sulfur atoms.
Molecules, Compounds, & Chemical Bonds Active Learning Activities
Functional Groups 26
The final functional group important to biological organisms is the phosphate group. Similar to the other
functional groups, the phosphate group plays an important role in a macromolecule. (The important
biological macromolecules are carbohydrates, lipids, proteins and nucleic acids.) All nucleic acids (which
are DNA and RNA) have a sugar-phosphate backbone, depending on the phosphate group for their
structure.
A Nucleotide [Author: OpenStax]
Nucleic acids (like proteins) are polymers, which means they have repeating subunits, like trains have
cars. The repeating subunit for nucleic acids are nucleotides (shown above). In this case, the sugar is
deoxyribose, which means this must be part of a DNA molecule since the sugar for RNA is ribose. The
nitrogenous base is guanine—there are four possible nitrogenous bases found on DNA: guanine,
cytosine, adenine and thymine.
19. What are the three parts of a nucleotide? The three parts of a nucleotide are a phosphate group, a sugar and a nitrogenous base.
[Author: OpenStax]
As you look along the “Sugar-Phosphate” backbone, you see why that is a perfect name for this
structure. DNA is a double-stranded molecule, like a twisted ladder, with the sugar-phosphate
backbones as the legs and the nitrogenous bases forming the rungs.
Molecules, Compounds, & Chemical Bonds Active Learning Activities
Functional Groups 27
20. Of the three parts of the nucleotide (sugar, phosphate, and nitrogenous base), which part is always the same, regardless if it’s on DNA or RNA.
The phosphate is the only part of a nucleotide that is always the same. DNA and RNA have different sugars, and there are 5 different nitrogenous bases.
DNA has deoxyribose for its sugar, while RNA has ribose for its sugar. DNA has cytosine, guanine,
adenine and thymine for its nitrogenous bases, while RNA replaces thymine with uracil. The only part of
DNA and RNA that is always the same is the phosphate group that makes up part of the backbone.
Another extremely important way a phosphate group plays an important role in biology is in the energy
currency for the cells.
Cellular processes need energy, but the energy-storing molecule (glucose) is too unwieldy and large to
be of much use to the cell. Instead, the energy from glucose must be converted to a more usable form:
adenosine triphosphate.
Adenosine Diphosphate Adenosine Triphosphate
Adenosine diphosphate (ADP) is like a partially charged battery. By linking one more phosphate onto
ADP, adenosine triphosphate (ATP) is formed and is able to supply energy to cellular process.
21. How many phosphate groups does ADP have? How many phosphate groups does ATP have?
ADP has two phosphate groups, while ATP has three phosphate groups.
22. Noticing that ATP and ADP both have a nitrogenous base (the two rings in the upper right), a sugar (the large pentagon) and a phosphate group, what kind of molecule are ADP and ATP?
Both ADP and ATP are nucleotides.
23. When ATP releases its energy for cellular processes, it also releases a phosphate group. With this in mind, where was the energy stored in the ATP molecule?
ATP stores its energy in the bond that links the final phosphate group.
Linking that third phosphate group onto ADP to form ATP is one of the most important steps in all of
biology and is called phosphorylation. There are three major ways phosphorylation occurs:
photophosphorylation (in photosynthesis), substrate-level phosphorylation (like in glycolysis), and
oxidative phosphorylation (in the electron transport chain during cellular respiration).
Molecules, Compounds, & Chemical Bonds Active Learning Activities
Hydrogen Bonds—Making Water Amazing 28
Section 3.4 Hydrogen Bonds—Making Water Amazing Directions for the Student:
This lesson is designed for you to complete, on your own or in your study group. Use your notes and follow along in the text, as you find necessary.
Objectives: 1. Describe conditions necessary for and the characteristics of hydrogen bonds. 2. Analyze the structure of water molecules and explain the results of their hydrogen
bonds. 3. Describe characteristics of water, including solvency, increasing chemical reactivity,
thermal stability and lubrication.
Polar covalent bonds are still covalent bonds, they just don’t share their electrons evenly. As a result,
there are partial charges on the atoms, and, as we all know, opposites attract.
Hydrogen usually does not pull the electrons as much as the atoms it bonds with. This means that
hydrogen atoms in polar covalent bonds will have a slight positive charge, and will be attracted to atoms
with a slight negative charge. This is called a hydrogen bond, but it is really just an attraction between
the polar ends with opposite charges.
1. Draw two water (H2O) molecules using sticks to show the bonds. Then draw the partial charges (with a lower case delta: ᵟ ) where appropriate. Add a dashed line between two polar ends with opposite charges to represent a hydrogen bond.
2. Predict what will happen when many water molecules get together. Specifically, discuss what will happen to the water as a collective group.
When water molecules align with each other, a weak bond is established between the negatively charged oxygen atom of one water molecule and the positively charged hydrogen atoms of a neighboring water molecule. The weak bond that often forms between hydrogen atoms and neighboring atoms is the hydrogen bond. Hydrogen bonds give water molecules two additional characteristics: cohesion and surface tension. Because of the extensive hydrogen bonding in water, the molecules tend to stick to each other in a regular pattern. This phenomenon, called cohesion, is easily observed as you carefully overfill a glass with water and observe the water molecules holding together above the rim until gravity overtakes the hydrogen bonding and the water molecules spill down the side of the glass. Likewise, the cohesive property of water allows tall trees to bring water to their highest leaves from sources below ground.
Molecules, Compounds, & Chemical Bonds Active Learning Activities
Hydrogen Bonds—Making Water Amazing 29
Water has an amazing ability to stick together. The hydrogen bonds formed between two molecules of
water give water great cohesion. But water doesn’t just stick to itself—it also sticks to other things.
Think about how much water sticks onto you when you get out of the swimming pool. The hydrogen
bonds help give water great adhesion too. (Think of adhesive tape sticking things together.)
Water is known as the universal solvent. Many things dissolve in water (think of adding salt to water and
watching it seemingly disappear). Solutions that have water as their solvent are referred to as aqueous
solutions, and life depends on them. Because water is polar, it can easily dissolve other polar things,
which is why ionic compounds like salt will break apart in water. Now that the ions are disassociated,
they can undergo chemical reactions.
3. Examine the data below for a reaction and write an EVIDENCE and CLAIM.
Amount of Water Added Time Required for Reaction
0 mL Did not react
5 mL 15 seconds
10 mL 5 seconds
Evidence Claim
No water = no reaction
The more water = faster reaction time
Water is required for the reaction to occur
Water speeds up the reaction time
If the particles are not dissolved in water, they may not react. And if they are not completely dissolved in
water, the reaction time will not be as quick—water increases chemical reactivity.
4. Examine the data below. The data is taken from two equal parts of water and soil (land) that were exposed to equal amounts of sunlight (energy. Complete an EVIDENCE and CLAIM.
Time Land Temperature (ᵒF) Water Temperature (ᵒF)
0 minutes 55 ᵒF 55 ᵒF
5 minutes 57 ᵒF 55 ᵒF
10 minutes 59 ᵒF 56 ᵒF
15 minutes 61 ᵒF 56 ᵒF
Molecules, Compounds, & Chemical Bonds Active Learning Activities
Hydrogen Bonds—Making Water Amazing 30
Evidence Claim
No exposure time = no change in temperature
More exposure time = higher changes in temperature
Time must be given for reactions to occur
The greater the exposure time = higher measured reactions
It takes a significant amount of energy to change the temperature of water—in other words, water has a
high heat capacity. This means that once water absorbs the heat, it keeps it. Also, when you sweat and
convert liquid water into gaseous water (or water vapor), it takes a lot of heat away from your body,
thereby, cooling you off!
5. Examine the data table below that measures the friction between two surfaces with different amounts of water between them, and make an EVIDENCE and CLAIM based on the data.
Amount of Water Between Two Surfaces Amount of Friction (newtons)
0 mL 5 N
5 mL 4 N
10 mL 3 N
15 mL 2 N
Evidence Claim
No water = high amount of friction
The higher the amount of water = lesser friction
Water must be present to reduce friction
Water functions as a lubricant
There are many parts of your body that rub against another part of your body. Without the lubrication
that water provides, any kind of movement would be difficult, at best.
Water is vital to life. Water helps us digest food, moves nutrients around our bodies, removes wastes,
send electrical messages in muscles and nerves, lubricates our moving parts, and regulates our body
temperatures. The chemical properties of water, including its hydrogen bonds, high heat capacity and its
ability to stay in its liquid form over a wide range of temperatures, give water amazing abilities and life
as we know it could not exist without water.
Molecules, Compounds, & Chemical Bonds Active Learning Activities
Solutions and Their Attributes 31
Section 3.5 Solutions and Their Attributes Directions for the Student:
This lesson is designed for you to complete, on your own or in your study group. Use your notes and follow along in the text, as you find necessary.
Objectives: 1. Describe the criteria used to define solutions, colloids and suspensions. 2. Identify three different types of “mixtures” through a verbal description, criteria or
through images. 3. Define and review the following terms: mole, concentration, molarity, solute,
solvent, Avogadro’s constant, buffer, homeostasis, osmosis, ion, acidic, basic, alkaline, neutral, and sodium chloride (NaCl).
4. Complete a Molarity calculation. 5. Describe how pH is determined and explain some characteristics of an acid and a
base. 6. Define a buffer and describe the importance of buffers used in allied health.
Substances get mixed up a lot in daily life. These mixtures have important biological consequences, and
are generally grouped into three categories: solutions, colloids and suspensions.
To understand this better, let’s look at something we all have: blood.
Component of Blood Approximate % Volume
in Blood
Size of Component
(nm = nanometer and µm = micrometer)
Water 50.6% 0.28 nm = 0.00000000028 m
H+ <0.1% 0.10 nm = 0.00000000010 m
Na+ <0.1% 0.18 nm = 0.00000000018 m
K+ <0.1% 0.22 nm = 0.00000000022 m
Ca+ <0.1% 0.18 nm = 0.00000000018 m
Cl- <0.1% 0.18 nm = 0.00000000018 m
HCO3- <0.1% 0.16 nm = 0.00000000016 m
Lipids <0.5% 2 to 5 nm = 0.000000002 m
Glucose <0.5% 0.8 nm = 0.0000000008 m
Amino Acids <0.5% 0.8 to 1.4 nm = 0.0000000008 m
Proteins 3.8% 15 to 20 nm = 0.000000015 m
Platelets <0.1% 2 µm = 0.000002 m
White Blood Cells <0.1% 10 µm = 0.000010 m
Red Blood Cells 44.9% 5 µm = 0.000005 m
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Solutions and Their Attributes 32
The main component of a mixture is the dispersion medium. All of the other components are
considered to be dispersed throughout the main component.
1. What is the dispersion medium of blood? Water
2. What is the range (smallest to largest) of the different components of blood?
0.10 nm – 10 µm
Scientists classify mixtures into three categories, based on the size of the component. The type of
medium you are dealing with depends on the size of the particle.
Particle Size Type of Mixture
Less than 1 nm Solution
1 nm – 1 µm Colloid
Greater than 1 µm Suspension
3. Using the table as a guide, review each component listed and determine what type of mixture it would be when it is mixed with water.
Component Size Type of Mixture
H+ 0.10 nm Solution
Ca+ 0.18 nm Colloid
Lipids 2 to 5 nm Colloid
Glucose 0.8 nm Solution
Platelets 2 µm Suspension
Red Blood Cells 5 µm Suspension
4. What type of mixture is blood? solution, colloid, and suspension
Blood is an unusual mixture—it is a solution, a colloid and a suspension.
Solutions are very important mixtures. As such, the parts of the solution get special names. The medium
doing the dissolving (usually water) is called the solvent. The particles (which are less than 1 nm) that
are dissolved in the solvent are called solutes.
5. What particles in blood are considered to be solutes? List all of them.
Water, H+, Na+, K+, Ca+, Cl-, HCO3-, Lipids, Glucose, Amino Acids
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Solutions and Their Attributes 33
Knowing how to work with solutions is very important in biology and chemistry. One way that we
understand solutions is to identify their concentrations, in terms of the number of solutes in one liter
(solutes per liter). This means we have to know the mass of the of the solutes. (Remember that the
MASS NUMBER refers to the number of protons and the number of neutrons combined, and that
different isotopes have different numbers of neutrons. With this in mind, the average atomic mass is an
average of all of the isotopes.) But where can we find the mass of individual atoms?
Once again, the periodic table comes to the rescue.
Below each element is its average atomic mass (given in atomic mass units or amu). Because we don’t
always know exactly which isotope it is, we will use the average atomic mass. There may be times when
you do know exactly which isotope is being used. Using the periodic table as your guide, answer these
questions.
6. The first solute on the list is H+. What is the mass of one hydrogen atom?
1.008 amu
Hopefully you found the “1.008” amu underneath hydrogen on your periodic table. If you did not, make
sure you know where it is now, before moving on.
7. If one hydrogen atom has a mass of 1.008 amu, what is the mass of 2 hydrogen atoms?
2.016 amu
When there are multiple atoms, we can simply multiply by how many there are. Did you multiply 1.008
amu by 2?
8. What is the mass of a sodium atom? (Again, use the average atomic mass.)
22.990 amu
Now we will find the mass of a molecule. Add the mass of each atom together to find the mass of the
molecule.
9. What is the mass of one molecule of sodium chloride (NaCl)?
58.443 amu
One sodium is counted as 22.99 amu and one chlorine atom is counted as 35.4527 amu. Therefore, a
sodium chloride molecule will be 58.4427 amu.
10. What is the mass of ten sodium chloride molecules? 584.43 amu
Molecules, Compounds, & Chemical Bonds Active Learning Activities
Solutions and Their Attributes 34
11. What is the mass of 100 sodium chloride molecules? 5,844.3 amu
Unfortunately, there is not a balance that measures substances in amu’s. What we have been doing is
simply a thought experiment, and it would be extremely difficult to ever measure individual atoms or
molecules. If we only have balances that measure in grams (the ones in our labs usually measure to a
hundredth of a gram), how could we possibly use grams to approximately know how many molecules
there are in a sample? What do we need to solve this dilemma? (Think about these questions for a
moment before moving on.)
If we know how many atoms are in amu’s and can only measure in grams, we have to have a bridge
between amu’s and grams. We must have a conversion from amu’s to grams. But what is this magical
number that can convert amu’s to grams?
To understand this magical number, let’s do another thought experiment. Imagine you went outside and
started to catch individual carbon atoms and put them onto a scale as you counted them. While you
added more and more (1, 2, 3, 4, 5, . . . ) carbon atoms, when you reached a certain number, the scale
would read 12.011g.
12. Why is 12.011 an important number for carbon? Refer to your periodic table.
It is the average atomic mass for Carbon
When you get to the point where the scale reads 12.011g of carbon atoms, you will have counted about
602 214 129 000 000 000 000 000 atoms of carbon. (Don’t be confused by the spaces—sometimes
scientists use spaces instead of commas with very large numbers.)
This is the magic number: 6.022 x 1023. It is often called the Avogadro constant, named after the Italian
scientist, Amedeo Avogadro, as tribute for his contributions to science.
The Avogadro constant is also called a mole (abbreviated as “mol”), and it is one of the base units in the
International System of Units.
1 mole = 6.022 x 1023
Instead of saying that we have 6.022 x 1023 particles, we just say that we have 1 mole of particles.
This means that we now have a conversion that will take us from amu’s to grams.
1 gram = 6.022 x 1023 amu’s
13. What is the mass of 1 mole of carbon atoms? 12.011 grams
14. What is the mass of 2 moles of carbon atoms? 24.022 grams
Molecules, Compounds, & Chemical Bonds Active Learning Activities
Solutions and Their Attributes 35
Just as before with more than one atom, if there are multiple moles, we multiply. One mole of carbon is
equal to 12.011g and 2 moles is equal to 24.022g.
15. What is the mass of 1 mole of sodium chloride? 58.44 grams
One mole of sodium has a mass of 22.99g and one mole of chlorine has a mass of 35.4527g, so their
combined mass is 58.4427g
16. What is the mass of 5 moles of sodium chloride? 292.2 grams
17. Glucose is C6H12O6. What is the mass of 1 mole of glucose? Complete the table below first, then answer.
180.162 grams
Element Mass of 1 mole Number of Atoms Total Mass for Element
Carbon 12.011g 6 72.066g
Hydrogen 1.008 grams 12 12.096 grams
Oxygen 16 grams 6 96 grams
Total mass for glucose: 180.162 grams
18. How many moles of sodium chloride (NaCl) are there in 58.4427g?
1 mole
EXAMPLE: How many moles are in 350.6562g of NaCl? Setting up this problem properly is of the utmost
importance.
1 mole of NaCl is to 58..4472g of NaCl as ___x___ moles of NaCl is to 350.6562g of NaCl
1 𝑚𝑜𝑙 𝑜𝑓 𝑁𝑎𝐶𝑙
58.4472𝑔 𝑜𝑓 𝑁𝑎𝐶𝑙=
𝑥 𝑚𝑜𝑙 𝑜𝑓 𝑁𝑎𝐶𝑙
350.6562𝑔 𝑜𝑓 𝑁𝑎𝐶𝑙
350.6562𝑔 𝑜𝑓 𝑁𝑎𝐶𝑙 × 1 𝑚𝑜𝑙 𝑜𝑓 𝑁𝑎𝐶𝑙
58.4472𝑔 𝑜𝑓 𝑁𝑎𝐶𝑙=
𝑥 𝑚𝑜𝑙 𝑜𝑓 𝑁𝑎𝐶𝑙
350.6562𝑔 𝑜𝑓 𝑁𝑎𝐶𝑙 ×350.6562𝑔 𝑜𝑓 𝑁𝑎𝐶𝑙
350.6562𝑔 𝑜𝑓 𝑁𝑎𝐶𝑙 (1 𝑚𝑜𝑙 𝑜𝑓 𝑁𝑎𝐶𝑙)
58.4472𝑔 𝑜𝑓 𝑁𝑎𝐶𝑙= 𝑥 𝑚𝑜𝑙 𝑜𝑓 𝑁𝑎𝐶𝑙
350.6562
58.4472 (1 𝑚𝑜𝑙 𝑜𝑓 𝑁𝑎𝐶𝑙) = 𝑥 𝑚𝑜𝑙 𝑜𝑓 𝑁𝑎𝐶𝑙
Molecules, Compounds, & Chemical Bonds Active Learning Activities
Solutions and Their Attributes 36
6 𝑚𝑜𝑙 𝑜𝑓 𝑁𝑎𝐶𝑙 = 𝑥 𝑚𝑜𝑙 𝑁𝑎𝐶𝑙
There are 6 moles of sodium chloride in 350.6562 grams of sodium chloride.
19. How many moles of carbon dioxide (CO2) are there in 132.027g of CO2? (Hint: First, find the number of grams in one mole of CO2, then set it up like the example.)
3 moles
20. How many moles of H2O are there in 95.4795 grams of H2O? (Hint: The number of moles may not always be a whole number.)
5.3 moles
Now that you understand moles, you can start to examine a very important aspect of solutions:
molarity.
𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦 = 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑀𝑜𝑙𝑒𝑠
𝑙𝑖𝑡𝑒𝑟
EXAMPLE: There are 3 moles of glucose dissolved into 1 liter of solution. What is the molar
concentration of the solution?
𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦 = 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑀𝑜𝑙𝑒𝑠
𝑙𝑖𝑡𝑒𝑟=
3 𝑚𝑜𝑙
1 𝐿= 3
𝑚𝑜𝑙
𝐿
This is the same as saying it is a 3 molar solution (or 3 M solution).
21. What is the molar concentration of a solution that has 2 moles of sodium chloride dissolved in 4 liters of solution?
0.5 mol/L
Molecules, Compounds, & Chemical Bonds Active Learning Activities
Solutions and Their Attributes 37
22. What is the molar concentration of a solution with 7 moles of sodium chloride dissolved in 3 liters of solution?
2.3 mol/L
23. What is the molar concentration of a solution with 1 mole of solute in 15 liters of solution?
.06 mol/L
Water is made up of two hydrogen atoms and one oxygen atom. What would happen if you split water
up?
H2O H+ + OH-
Normally, the arrow in the middle stands for “yields” or “turns into” and only points to the right. This
arrow points both ways to symbolize that this reaction can go back and forth, and that is exactly what
happens in water all the time. The “H+” ion is a hydrogen ion and the “OH-“ ion is called a hydroxide ion
(hydrogen and oxygen).
Most solutions in biology are aqueous solutions (solutions with water as their solvent). And we know
that life would not be possible without water. Therefore, understanding the characteristics of water is
very important.
24. When water is split into the hydrogen ion and the hydroxide ion, why are there charges on the ions?
Hydrolysis is a chemical process of adding a water molecule to a compound which most often causes both parts to break their chemical bonds resulting in each fragment becoming either an anion (negatively charged ions like hydroxide ions, OH-) or a cation (positively charged ions like hydrogen ions H+). The oppositely charged ions attach to each other synthesizing into new substances. Often these reactions take place when ionic compounds dissolve in water.
Remembering how strong the oxygen pulls electrons (it has a high electronegativity), it is easy to see
that the oxygen will pull the electron away (making the charge on the hydroxide negative 1) from the
lone hydrogen ion (making the charge on the hydrogen positive 1).
Molecules, Compounds, & Chemical Bonds Active Learning Activities
Solutions and Their Attributes 38
A very common measure of water quality is pH. The pH of a solution is a measure of the molar
concentration of hydrogen ions. Some say that the “pH” stands for the “power of hydrogen”. Most of
the time, the concentration of hydrogen ions is very small.
25. What is the molar concentration of a solution that has 0.01 moles of H+ ions in 1 liter of solution?
o.o1 mol/L
Having a 0.01 M solution may sound like a small amount, but, as we will soon see, that would be a
strong acid.
26. Using the evidence below, complete the two EVIDENCEs and one CLAIM. (Notice that hydrogen ion concentration is abbreviated by [H+]. Brackets are commonly used to denote concentration.)
Hydrogen Ion Concentration (mol/L)
[H+] pH
0.00000000000001 = 1 x 10-14 14
0.0000000000001 = 1 x 10-13 13
0.000000000001 = 1 x 10-12 12
0.00000000001 = 1 x 10-11 11
0.0000000001 = 1 x 10-10 10
0.00000001 = 1 x 10-9 9
0.00000001 = 1 x 10-8 8
0.0000001 = 1 x 10-7 7
0.000001 = 1 x 10-6 6
0.00001 = 1 x 10-5 5
0.0001 = 1 x 10-4 4
0.001 = 1 x 10-3 3
0.01 = 1 x 10-2 2
0.1 = 1 x 10-1 1
1 = 100 0
Molecules, Compounds, & Chemical Bonds Active Learning Activities
Solutions and Their Attributes 39
Evidence Claim
I notice that the concentration is getting larger (as you move down the table) while the pH is getting smaller…
This means that, as the hydrogen ion concentration increases, pH…
I notice that when the hydrogen concentration is written in scientific notation with an exponent, the exponent seems to be related to the pH…
This means that the pH is related to the…
We will study pH more when we study exponents. Seeing the above relationships is a good first step.
Most scales measure the pH scale from 0-14, but it is possible to have solutions with higher or lower
concentrations of hydrogen ions that will result in a pH value of less than zero or greater than 14.
Pure water has a perfect balance of hydrogen ions and hydroxide ions, and it has a pH of 7 (any solution
with a pH of 7 is considered to be pH “balanced”). A solution with a pH below 7 is considered to be
acidic. Any pH above 7 is considered to be alkaline. (Note: A solution with the pH of 8 would be a base,
but we don’t usually say it is basic—rather, we say that solution is alkaline.)
Weak acids will have a pH close to 7. For example, a solution with a pH of 5 or 6 would be a weak acid.
Similarly, weak bases will have a pH close to 7. For example, a solution with a pH of 8 or 9 would be a
weak base. The further away from a pH of 7 you get, the stronger the acid or the base becomes.
Because a pH of 7 has an equal number of hydrogen ions and hydroxide ions, a pH of 7 is considered to
be balanced. Acids have more hydrogen ions and bases have more hydroxide ions.
Molecules, Compounds, & Chemical Bonds Active Learning Activities
Solutions and Their Attributes 40
27. Urine has a pH somewhere around 6 (although it can vary). What type of solution (acid or base) is urine? Does urine (with a pH of 6) have more hydrogen ions or more hydroxide ions? (Remember, there are many other particles that are in urine; pH is just looking at the hydrogen ion concentration.)
Urine is a weak acid. It has more hydrogen ions.
28. Blood has a pH of 7.4, and its variation is quite small. The pH of human blood must remain between 7.35 and 7.45 or there will be severe complications. Is human blood acidic or alkaline? Does blood have more hydrogen ions or more hydroxide ions in it?
Human blood is slightly alkaline. It has more hydroxide ions than hydrogen ions.
29. Cranberry juice has a pH around 2.5, which makes it a somewhat strong acid. Various parts of our metabolism create acids in our bodies. How can we keep our blood pH within that narrow window of 7.35-3.45? What helps regulate changes in pH?
Buffer systems. Urinary, respiratory, and integumentary systems.
30. Complete an EVIDENCE and CLAIM for the data below that shows acid being added to two solutions. Solution A and Solution B are identical in all ways except one. After the EVIDENCE and CLAIM, you will hypothesize about this difference.
Solution A Solution B
Acid Added (ml) pH Acid Added (ml) pH
0 7 0 7
1 6 1 7
2 5.2 2 7
3 4.7 3 6.9
4 4.4 4 6.8
5 4.2 5 6.8
6 4 6 6.7
Evidence Claim
I notice that the more acid added to solution A the faster that the pH drops
I notice that the more acid added to solution B the that the pH drops slower
There is less hydroxide ions in solution A
There is more hydroxide ions in solution B
Molecules, Compounds, & Chemical Bonds Active Learning Activities
Solutions and Their Attributes 41
31. What could cause the difference in the two solutions? (Hint: Think about what acids have excess of.)
There are more hydroxide ions in solution B than A
Acids have a lot of hydrogen ions. Therefore, when acid was added to the solutions, we were essentially
adding extra hydrogen ions. But what happened to those extra hydrogen ions in Solution B?
If the pH didn’t change much that means that the extra hydrogen ions must have bonded with another
atom or group of atoms. If the hydrogen ions are bonded, they are no longer counted in the hydrogen
ion concentration and, therefore, do not lower the pH. In this way, your blood can absorb hydrogen ions
and keep the pH relatively stable. These stabilizing molecules that remove hydrogen ions are called
buffers and we couldn’t live without them.