1. Ch 2
The chemistry of life

2. 2.1 Atoms make up all matter
A. Elements are fundamental types of matter
Elements are pure substances
They are organized into the periodic table of elements.
Only about 25 elements are essential to living things.
C,H,O,N are the most abundant
Minerals are essential elements other than CHON
P, Na, Mg, K, Ca are bulk elements- others are trace elements and you need only a small amount
You can get very sick from missing minerals in your diet!

3. B. Atoms are particles of elements
Atom- smallest unit of matter(made of protons, neutrons and electrons)
Protons and electrons are equal- if not the atom is an ion(it has a net charge) these are important to living things.
C. isotopes have different numbers of neutrons-
Mass numbers= protons + neutrons
Isotopes are atoms with a varying number of neutrons- these can be radioactive- each radioactive isotope has a characteristic half life- these are important for science and medicine

4. 2.2 Chemical bonds link atoms
Molecule- two or more atoms chemically bonded together.
Compound- molecule composed of two or more different elements.
Characteristics of a compound are very different than the characteristics of the elements that make it up.
A. electrons determine bonding- orbitals, energy shell, valence shell- know these terms

5. B. Covalent bonds share electrons
Most of the bonds in biological molecules are covalent bonds.
They are not always shared equally as is the case with electronegativity.
Nonpolar covalent bond- attractive force of each nucleus of the atoms is equal.
Polar covalent bonds- like in water- one atom exerts a greater attractive force. Oxygen is highly electronegative, so water is a polar molecule.

6. C. Ionic bonds transfer electrons
Ionic bonds result from the attractive force between ions.
Salt is an example (NaCl)
D. Partial charges on polar molecules create hydrogen bonds
In a hydrogen bond, opposite partial charges on adjacent molecules-or within a single large molecule- attract each other.
Relatively weak bond that is very important in biology.

7. 2.3 water is essential to life. A. Water is cohesive and adhesive
Hydrogen bonds contribute to water being cohesive
Cohesion- tendency of water to stick together(think surface tension)
Adhesion is the tendency of water to form hydrogen bonds with other substances(think capillary action)

8. B. Many substances dissolve in water
Water is essential to life because it can dissolve many substances.
Solvent- does the dissolving (aqueous means water is the solvent)
Solute- what is being dissolved
Solution- made of one or more solutes dissolved in a given solvent

9. 2 categories of chemicals based on affinity for water
Hydrophilic- either polar or charged and dissolves easily in water(sugar, salt, ions like electrolytes)
Hydrophobic- nonpolar molecules made of carbon and hydrogen like fats and oils do not dissolve in water.

10. C. Water regulates temperature
Water resists temperature change.
A lot of heat is needed to evaporate water.

11. D. Water expands as it freezes
Helps keep ponds from freezing from the bottom up.

12. E. Water participates in Life’s chemical reactions
Life depends on thousands of simultaneous chemical reactions.
A chemical reaction occurs when two or more molecules swap their atoms to yield different molecules.
Reactants- starting materials
Products- ending materials

13. 2.4 organisms balance acids and bases
A chemically neutral solution would have the same number of H+ and OH- ions.
An acid is a chemical that adds H+ ions making them outnumber the OH- ions. (examples, H2SO4 and HCl)
A base is opposite of an acid: it makes the concentration of OH- ions greater. (examples, baking soda and NaOH)
Acids and bases neutralize each other.
Both are important in every day life.

14. A. The pH scale expresses acidity or alkalinity
7 is neutral
pH < 7 is an acid
pH > 7 is a base
All organisms have pH requirements. Human blood should be between 7.35 to 7.45.
Too much variation either direction can be deadly

15. B. Buffer systems regulate pH
pH is regulated in living things by buffering systems. These are pairs of weak acids and bases that resist changes in pH.