unit 2a: basic chemistry

CP Biology 2016 Name KEY

UNIT 2A: Basic Chemistry

Chapter 2: The Chemistry of Life

2.1 – The Nature of Matter

Living things share a major fundamental similarity with

nonliving matter. All matter is made up of atoms.

*Atom: the basic unit of all matter

Atoms are incredibly small in size, yet they themselves are

made of even smaller subatomic particles called

protons, neutrons and electrons.

Protons and Neutrons have about the same mass but not the

same electrical charge.

Protons and neutrons are bound by strong forces which

form the nucleus or center of the atom.

The electron is a charged particle with 1/1840th the mass of

a proton. The energy of their constant motion keeps them

outside the nucleus, despite their attraction to the nucleus.

Because atoms have equal numbers of electrons and

protons, their positive and negative charges balance out

and atoms themselves are electrically neutral.

The Structure of an Atom

Complete the Chart Below:

Subatomic Electrical Location

Particle Charge within atom

proton

+1

positive

nucleus

neutron

0

neutral

nucleus

electron

-1

negative

Moving rapidly in energy

levels (electron cloud)

surrounding the nucleus

Your personal notes, summary of the lesson, and/or questions that you may have:

1


A chemical Element is a pure substance that consists

entirely of one type of atom.

More than 100 elements are known, but only about two

dozen are commonly found in living organisms.

________________________________________________

The Periodic Table of Elements is a reference tool we use to

gain information about different elements. Elements are

arranged in order by their atomic number. By using the

periodic table we can determine 3 things:

1) Element Name and Symbol – a symbol is usually 1

or 2 letter abbreviation for the element’s name.

2) Mass Number – this is the sum of the protons and

the neutrons in the nucleus. The electrons don’t count

in the mass since their mass is next to nothing.

3) Atomic Number – the number of protons in the

nucleus of an element.

Element Name and Symbol

1) ___C____ is the symbol for Carbon

2) Na is the symbol for ___Sodium_______

Mass Number

You may see a decimal number for the mass on the periodic

table because this is the average mass for the atoms of this

element. Some atoms differ slightly in mass due to different

number of neutrons. These are called isotopes and will be

studied next year in Chemistry. For Biology class we will round

this number to the nearest whole number.

3) The mass of Oxygen is ___16 amu________

4) The mass of Chlorine is ____35 amu________

Atomic Number

5) The atomic number of Hydrogen is ___1_______

6) The atomic number of Sodium is ____11______

Protons and Electrons

7) Carbon has __6___ protons and __6___ electrons.

8) Lithium has __3___ protons and __3___ electrons.

The five most abundant elements in living things are:

1. Hydrogen – 10%

2. Oxygen – 65%

3. Nitrogen – 4%

4. Carbon – 19%

5. Phosphorus – 1%

Label the

Important

Biological

Elements

2

The Periodic Table of Elements (see picture of periodic table on the last page)

Important Biological Elements

Chemical Compounds

In nature, it is common to find elements combined with

other elements in compounds.

*Compounds / molecules: a substance formed by the

chemical combination of two or more elements

in definite proportions.

*Coefficient: tells how many molecules of that substance

(the large number BEFORE the formula)

*Subscript: goes with the element symbol preceding the

number; tells how many atoms of that element within one

molecule of the substance (small number WITHIN the

formula.

The physical and chemical properties of a compound are

usually very different from those of the original elements

from which it is formed.

Example : NaCl (Table Salt)

NaCl is formed from one atom of sodium a highly reactive,

soft, silver-colored metal AND one atom of chlorine a

poisonous yellow-green gas.

Chemical formulas tell us:

a) They types of elements (atoms) that are present in the

compound.

b) The number of atoms of each element present in the

compound.

We show the composition of chemical compounds by a

kind of shorthand known as a chemical formula.

Example 1: What is the chemical formula for water which

contains two hydrogen atoms and one oxygen atom?

__H2O___

Example 2: 6CO2

a) What is the coefficient? __6_____

b) What is carbon’s subscript? __1______

c) What is oxygen’s subscript? ___2_____

d) How many molecules of this compound are

represented by this formula? __6_______

e) How many atoms TOTAL are present in this

molecule? ___18______

Use the following information on chemical names and

chemical formulas to fill in the chart below:


3

Carbon – 1

Hydrogen - 4

Hydrogen – 2

Oxygen - 1

Carbon - 1

Oxygen - 2

Nitrogen - 1

Hydrogen - 3


Chemical Bonds

The atoms in compounds are held together by various types

of chemical bonds.

Bond formation involves the electrons that surround each

atomic nucleus.

*Valence Electrons: the electrons in an atom that are

available to form bonds (these are unpaired electrons

which are found in the outermost energy level of the

atom’s electron cloud).

*Octet Rule: the outermost energy level of most atoms will

be complete when containing 8 electrons. Atoms will tend

to gain, lose, or share electrons to achieve stability by

having a full outer energy level (stable octet).

Exception: for hydrogen, the Duet rule applies (only

2 electrons are needed in the valence level)

The main type of bond that we will study in the unit is the

covalent bond.

Only reactive atoms are able to form bonds.

The reactivity of an atom depends upon the arrangement of

electrons in its outmost (or valence) energy level.

~ Do you think Carbon, Oxygen, Nitrogen and Hydrogen

are reactive (unstable) atoms? Explain. Yes, in each case, there is a vacancy in the outer energy level. H

has one vacancy in the 1st energy level. O has 2 vacancies in the

2nd

energy level. Nitrogen has 3 vacancies and Carbon has 4.

~ What can reactive /unstable atoms do to become

nonreactive /stable? (Recall that a stable atom has a fully

filled outer energy level.) They can interact with other atoms by gaining, losing or sharing

electrons to complete the atom’s valence energy level.

4

*Covalent Bonds

Formed when nonmetal atoms bond with each other

A bond in which moving electrons actually travel

about the nuclei of two atoms (at the same time)

Electrons are shared between two atoms

Single Covalent Bond: atoms share 2 electrons (1 pair)

Double Covalent Bond: atoms share 4 electrons (2 pairs)

Triple Covalent Bond: atoms share 6 electrons (3 pairs)

*Molecule: the structure that results when atoms are

joined together by covalent bonds. The smallest unit of

most compounds.

NOTE: Bonds between the biologically important atoms

H, O, N, C, & P (all non-metals) will be covalent.

Hydrogen will only form Covalent Bonds!!

Molecules can also be represented by Structural

Formulas: a drawing that shows the arrangement of atoms

in a molecule

Structural Formulas tell you:

a) the types of elements in the molecule

b) the number of atoms of each element AND

c) the arrangement of atoms and location of covalent

bonds. Shows the two dimensional shape of the

molecule.

Example 1: Water (H2O)

Example 2: Methane (CH4)


5

H O N C

1 2 3 4

NOTE: Structural formulas usually represent covalent

bonding so they are used for molecules like H2O, but not

for formula units like NaCl.

In a structural formula, each line between atoms represent

a position in which electrons are shared. Therefore, a line

represents a single covalent bond.

1) Hydrochloric Acid (Hydrogen Chloride) or HCl

___1__ atoms of Hydrogen in the molecule

___1__ atoms of Chlorine in the molecule

H - Cl

2) Ammonia or NH3

__1___ atoms of Nitrogen in the molecule

__3___ atoms of Hydrogen in the molecule

H

N – H

H

3) Oxygen gas or O2

___2__ atoms of Oxygen in the molecule

O = O

4) Carbon Dioxide or CO2

__1___ atoms of Carbon in the molecule

__2___ atoms of Oxygen in the molecule

O = C = O


6

2.4 Chemical Reactions

Note: We will not be discussing Enzymes in this unit.

*Chemical Reactions: process that changes or transforms

one set of chemicals into another set of chemicals. Involves

changes to the chemical bonds that join atoms in

compounds.

Bonds of the reactants are broken and new bonds form in

the products.

*Reactants: elements or compounds that enter into a

chemical reaction

*Products: elements or compounds produced by a

chemical reaction

HINT: Reactants react to produce products!

*Chemical Equations: a mathematical representation of a

chemical reaction. It shows the numbers and types of

compounds involved.

*The Law of Conservation of Matter: matter (atoms and

elements) in a chemical reaction cannot be created nor

destroyed. Only the arrangement of the atoms is changed,

NOT the number or types.

The numbers and types The numbers and types

of atoms in the = of atoms in the

__reactants___ __products___

Use the chemical formulas below to determine how many

atoms of each element make up each compound.

A coefficient indicates the number of molecules present.

(coefficient X subscript = the number of atoms)


7

Consider the following chemical equation for cellular respiration:

In the diagram below, fill in the terms “products” or “reactants” in the proper blanks.

6O2 + C6H12O6 6CO2 + 6H2O


8

Reactants

C – 6, H – 12, O – 18

Products

C – 6, H – 12, O – 18

CP Biology Name

PRACTICE PACKET

General Chemistry

#1 Periodic Table

Use the following terms to fill in the blanks for questions 1-8:

protons mass number neutrons energy levels nucleus symbol electrons atomic number

1) The periodic table is arranged in general order of increasing a) ___________________________,

b) _____________________________ and, c) _______________________________.

2) Each element in the table has a different a) ______________________, b) ______________________,

c) ___________________________, and d) ____________________________.

3) The number of protons in the nucleus of an atom is the same as the a) ______________________, and

b) __________________________________.

4) The large letter(s) that represent each element is called a _______________________________.

Complete the diagram by labeling all the parts.

5)

6)

Made up of 7) and 8)

9)

12) Complete the following table by placing a check in each box that makes the statement true:

Characteristic Electron Proton Neutron

Has nearly no mass

Positively charged

Found in the nucleus

Moves in energy levels

Added together to make the mass number or atomic

mass (weight)

Does not have an electrical charge

Negatively charged

13) Use the Periodic Table of the Elements to complete the following table.

Note: Add the names and information for three elements of your own choosing:

ELEMENT

SYMBOL

ATOMIC

NUMBER

MASS

NUMBER

*

NUMBER OF

PROTONS

NUMBER OF

ELECTRONS

HYDROGEN H 1

NITROGEN 7 14 7 7

CARBON 12

Na 11 23 11 11

CHLORINE Cl 17

SILVER 47 47 47

Pick 3 more elements:

*Note: Remember to round off the atomic weight to obtain the mass number or atomic mass.

In any neutral atom, the number of ___________________ is always equal to the number of

___________________.

#2 Subatomic Particles

You will become more familiar with the atomic structure of some atoms by completing the chart below. For each element,

you have been given enough information to fill in all the blanks. Use the periodic Table.

Element Symbol Atomic

Number

Mass Number Number of

Protons

Numbers of

Neutrons

Number of

Electrons

Helium

He

2

4

2

Iodine

I

53

73

Neon

Ne

10

20

10

Zirconium

Zr

91

51

40

Aluminum

Al

27

13

74

Zn

30

35

Kr

48

36

Calcium

40

B

5

Sodium ion

Na+

11

10

S2-

Chlorine Ion

Hydrogen Ion

1

0

(no, it’s not a

typo)

#3 Reactivity of Atoms

In biology we are concerned about how atoms join each other to form molecules like hydrogen gas (H2), carbon dioxide

(CO2) and glucose (C6H12O6). The tendency of atoms to bond with each other depends on their reactivity.

The reactivity or combining capacity of an atom depends upon the arrangement of electrons in the outermost energy

level, known as the valence. Circle the correct term in parenthesis for each sentence below.

1. If an atom’s outermost energy level is completely filled with electrons (no vacancies), the atom considered (

stable / unstable ) and nonreactive. Therefore, it ( will / will not ) form bonds with other atoms.

List three examples of nonreactive elements: ___________________________________________________

On the Periodic Table, where do we find the nonreactive elements?

Nonreactive elements are also known as the “ ________________ Gases”.

2. If an atom’s outermost energy level is not completely filled with electrons (vacancies present), the atom is

considered ( stable / unstable ) and reactive. Therefore, it ( will / will not ) combine with other atoms.

Examples of reactive atoms:

Element

Symbol

Atomic

Number

# electrons

Draw the electrons in their

energy levels

Reactive (R)

or non-reactive

(NR)

Carbon

C

Hydrogen

H

Oxygen

O

Nitrogen

N

Magnesium

Mg

Silicon

Si

Chlorine

Cl

Argon

Ar

#4 Electrons and the Reactivity of Atoms

Directions: Place the answer to the following questions on the line provided.

______1. Energy levels are:

a. the charge of protons c. the definite locations of electrons

b. the charge of atoms d. the probable locations of electrons

______2. If an atom is reactive, how does it become stable?

a. join a water molecule

b. join the nuclei of other atoms

c. form energy levels with other subatomic particles

d. form bonds with other reactive atoms

Directions: Smiley Cyrus was a student at Livingston High School. Below are her drawings of Bohr models for atoms of

three different elements. Check Smiley Cyrus’s work – each diagram has TWO mistakes. Your task is to fix her

errors.

* P=protons N=neutrons E= Electrons = electrons in energy levels

Nitrogen Argon Hydrogen

Circle the atom(s) below that are reactive. Put a triangle around the atom(s) below that are nonreactive.

N Ar H K C O He

How many electron vacancies are in the valence of each of the following atoms?

N Ar H K C O He

#5 Bohr Models and Lewis Dot Structures

1. What is the maximum number of electrons that can be found in the first energy level?

2. What is the maximum number of electrons that can be found in the second energy level?

3. For any atom with an atomic number greater than 2, the maximum number of electrons that can be found in the

outermost energy level (valence) is: __________. This is known as the Octet Rule. An atom with a full valence is

nonreactive and stable.

4. Draw a Bohr Model and Lewis Dot Structure for each element below. Follow the example given.

Element Bohr Model

Lewis Dot Structure

Number of electron

vacancies in valence

Sulfur (S)

2

Phosphorous(P)

Fluorine (F)

Neon (Ne)

Lithium (Li)

#6 Bonding Patterns

1) What is the purpose of bonding? __________________________________________________________

________________________________________________________________________________________

2) Is one atom of carbon stable?__________________ Why or why not?____________________________

_______________________________________________________________________________________

3) How many electrons will an atom of carbon share with another atom in order to become stable? ________

4) List the two most common types of bonds that can form between atoms:

a)_________________________ (sharing of e-) b) ______________________ (transfer of e-)

5) A _________________________is a shorthand way of showing the types and numbers of atoms in a molecule or

compound. For example, H2O indicates that one atom of oxygen has bonded with two atoms of hydrogen.

Circle the correct term in parenthesis:

The ( coefficient , subscript ) indicates how many atoms of the preceding element are found in the molecule.

The (coefficient , subscript ) indicates how many molecules of each compound are present.

In order to determine the number of atoms in a formula with a coefficient, ( multiply , add , divide ) the coefficient and

the subscript. Any time you don’t see a coefficient, you can assume it is “1”; the same is true for a subscript. (example:

the chemical formula CO2 indicates one molecule of carbon dioxide which contains one atom of carbon and two atoms of

oxygen).

Complete in the following chart:

Chemical Formula Total Number of atoms of each element

2H2O Four hydrogen atoms and two oxygen atoms.

CaCO3

2H2O

6H2SO4

Directions for drawing structural formulas:

A structural formula is a drawing of the atoms in a compound and the number of bonds between atoms. The short lines

in a structural formula represent a covalent bond (or a shared pair of e-) that has formed between two atoms. A single

bond is represented by a single line (-). A double bond is shown with two lines (=). A triple bond would contain 3 lines

().

Example H2O or water :

One water molecule contains ___ atom(s) of hydrogen and ____ atom(s) of oxygen.

Hydrogen (H) has one electron and one vacancy in its valence. So, it needs ___ bond(s) to be stable.

Oxygen (O) has six electrons in its valence (which means 2 vacancies). So, it needs ___ bond(s) to be stable.

By joining together, the atoms can share electrons in a way that makes all three atoms stable, each with a full valence.

The compound is stable and neutral overall because the total #p is still equal to the total #e-.

The way to represent this is to draw:

H O H In this way, the two atoms of hydrogen are bonded with one

atom of oxygen. The hydrogen atoms each have one bond and

the oxygen atom has two bonds.

Try these examples:

Draw the structural formulas for the following compound. Follow the models.

H2

# bonds each hydrogen can form? _____1______

H H

N2

# bonds each nitrogen can form? _________

CH4

# bonds carbon can form?_____

each hydrogen?____

H2O2

# bonds each hydrogen can form? _____

each oxygen? _____

PCl3

# bonds needed by each phosphorus? _______

each Cl?_______

O2

# bonds needed by each oxygen? _________

HCN (Hydrogen cyanide) H2O

#7 Counting Atoms

Calculate how many atoms of each element are present in each of the following (as written).

1. 3NaHCO3

2. 5C2H4O2

3. 2Mg(OH)2

4. 6H3 PO4

5. H2SO4

6. (NH4)3PO4

7. C6H12O6

8. 5CaCO3

#8 Recognizing Balanced Equations

Remember, in a balanced chemical equation, the number of atoms of each element in the

reactants will equal the number of atoms of each element in the products.

EQUATION

IS IT BALANCED,

as written? (Y/N)

A.

2C2H

6 + 5O

2 --> 2CO

2 + 6H

2O

B.

2H2O

2 --> 2H

2O + O

2

C.

Na + O2

--> 2Na2O

D.

N2 + 3H

2 --> 2NH

3

E.

P4 + 5O

2 --> P

4O

10

F.

3Fe + 4H2O --> Fe

3O

4 + 4H

2

G.

C + 2H2 --> CH

4

H.

Al2O

3 --> Al + 3O

2

I.

H2

+ O2 --> H

2O

2

J.

Na2SO

4 + CaCl

2 --> CaSO4 + 2NaCl

#9 Balancing Equations

Answer the following questions. Use complete sentences when given one or more lines to respond.

State the Law of Conservation of Matter:

To balance an equation, coefficient(s) may be added/removed/changed but subscripts cannot.

Balance each of the following equations.

H2 + Cl2 HCl

Fe + O2 Fe2O3

C6H12O6 + O2 CO2 + H2O

H2O + Cl2O3 HClO2

C6H6 + O2 CO2 + H2O

1) What is meant by the terms: products and reactants in a chemical equation? How do we know which is which?

_______________________________________________________________________________________

_______________________________________________________________________________________

2) Explain what the subscript indicates. What does it mean if there is no subscript?

_______________________________________________________________________________________

3) Explain what the coefficient indicates. What does it mean if there is no coefficient?

_______________________________________________________________________________________

__

4) Explain why chemical equations must be balanced.

_______________________________________________________________________________________

_______________________________________________________________________________________

unit 2a: basic chemistry

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