chapter 2. introduction to “baby chemistry” life depends on chemistry we need to be able to...
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Chapter 2
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Introduction to “Baby Chemistry”
Life depends on chemistry
We need to be able to understand the chemistry before we move on to understand the rest of body
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Atom - the basic unit of matter
Atoms are made of 3 subatomic particles
1. Protons - positive charge2. Neutrons – neutral charge3. Electrons – negative charge
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Protons and neutrons are found in the atoms nucleus - The center of the atom
Electrons are found outside the nucleusElectron cloudThey are in constant motionAre attracted to positive charge of nucleus
but remain outside due to energy of motion
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What is the overall charge of the nucleus?
What is the overall charge of the electron cloud?
Nucleus (+) & Electron Cloud (-)Therefore, atoms are
neutral from equal numbers of protons and electrons
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Elements – pure substances that consist of entirely 1 type of atom
They are represented by 1, 2 or 3 letters
There are 117 elements (periodic table in back of book)
Based on certain characteristics of
each element
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Periodic table includes information on atomic mass and atomic number
Atomic Number – number of protons (and therefore electrons)
Atomic Mass – sum of protons and neutrons
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How are isotopes different?
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Q) How are isotopes different?
R) They have a different number of neutrons
Isotopes are identified by their atomic mass number (protons + neutrons)
All isotopes still have the same chemical properties (because neutrons are neutral)
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Have nuclei that are unstable and break down at constant rates over time
Important Uses1.Determine age of rocks2.Treat cancer and kill bacteria that cause
food to spoil3.Used as “tracers” to follow substances
in the body
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*In nature, most elements are found combined with other elements in compounds
• Compound – substances formed by the chemical combination of 2 or more elements
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What information is contained in a chemical formula?
1. Type of atoms2. How many of those atoms
Example) Q) What’s in H20?
A) 2 hydrogen and 1 oxygen
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Physical and chemical properties of a compound are usually different from those of elements from which they are formed
Example – NaClSodium Chloride : Table SaltSodium (Na) – silver colored metalChlorine (Cl) – greenish gas
+ =
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Hold compounds together
Involves the outer electrons (valence electrons) that surround each atom’s nucleus
3 types of bonds1. Ionic (strongest)2. Covalent3. Van Der Waals Forces (weakest)
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One or more electron is “transferred” from one atom to another
An atom that loses an electron has a positive charge
An atom that gains an electron has a negative charge
Positively or negatively charged atoms are called ions
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When electrons are “shared” instead of being “transferred”
How do they share electrons?The electron travels in the orbits of both
atoms
Single bond – 2 electrons shared Double bond – 4 electrons shared Triple bond – 6 electrons shared
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Atoms joined by covalent bonds are called molecules
Water Molecule
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Atoms in covalent bond don’t always share equally
Rapid movement of electrons creates “+” and “-” charges
When molecules are close together, an attraction can occur between oppositely charges regionCreates intermolecular “Vander Waals
Forces”
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How does the gecko’s foot function similarly to Van Der Waals Forces?
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The water molecule – H2O (think mickey mouse)
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Water is a polar molecule
What is polarity?The uneven distribution of electrons which
causes the molecule to have regions with a positive and negative charge
Allows water to attract to other molecules
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Most abundant compound in living things
Naturally occurring and found at any temperature on the earth
Water expands when it freezes, SO WHAT??How does that affect us?
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Held together by hydrogen bonds (not as strong as ionic or covalent) which form between the hydrogen and oxygen
Why would this be important?
How many bonds are there per water molecule?
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Allows 4 bonds to form
This bonding pattern is what makes water responsible for it’s many special properties
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CohesionAn attraction between water molecules
Why can a spider walk on waterHow does water come out of a faucet?
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AdhesionAn attraction of water to other molecules
How does a tree get water from its roots to its leaves?
Why does the water level in a graduated cylinder look curved?
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Mixture – a material composed of 2 or more elements or compounds that are physically combined, but not chemically combined
Examples: Chocolate Chip Cookie Earths Atmosphere
2 types of Mixtures1.Solution2.Suspension
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Is a mixture of 2 or more substances in which the molecules are evenly distributed
Example:Salt dissolving in water (the NaCl and H2O combine by the Cl- being
attracted to the H and the Na+ being attracted to the O)
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2 important terms to knowSolute – substance being dissolvedSolvent – substance doing the dissolving
Q) Why is water considered the greatest solvent in the world?
A) Polarity allows it to pull other molecules apart
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Mixture of water and non-dissolved material
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Concentrations for hydrogen (H +) and hydroxide (OH-) ions are important indicators of the properties of a solution
A measurement system was created to indicate the concentration of the H + ions in the solution called the pH scalepH – potential of hydrogen
A pH of 7 = equal number of H + and OH- ions
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A pH of 7 = equal number of H + and OH- ions
H + + OH- = H2O
Solutions with a pH < 7 are called acidsBecause more hydrogen ions (H +)
The lower the pH, the greater the acidity
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Solutions with a pH > 7 are called alkaline or basicBecause more hydroxide (OH-) ions
The higher the pH, the more basic the solution
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Each step of the pH scale represents a factor of 10
Ex) pH of 4 has 10x as many H + ions as a solution with a pH of 5
Acids BasesI-------------------------I-------------------------I
1 H + > OH- 7 H + < OH- 14H + = OH-
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Weak acids or bases that can react with strong acids or bases to prevent sharp, sudden changes in pH
Why are buffers important?The pH of fluids within most cells of the
human body must generally be kept between 6.5 and 7.5
If pH is higher/lower – it will affect the chemical reactions that take place
Controlling the pH of cells is important for maintaining homeostasis
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