1. The Chemical Context of Life
CHAPTER 2

2. Matter anything that takes up space and has mass
pure forms are called elements
combined forms are called compounds
92 elements occur in nature…25 elements are essential for life
96% of living matter is composed of 4 elements: C,H,O,N
most of the remaining 4% is composed of P, S, Ca, and P

4. Atomic Structure
atom – smallest unit having the properties of its element
subatomic particles: e, p+, n0
nucleus (p+ & n0)
electron shells
1st: max 2e
2nd: max 8e

6. Periodic Table of Elements
provides information about atoms
atomic number
atomic mass

7. isotopes = atoms with extra n0 radioactive isotopes
atomic number = # of p+
atomic mass = p+ + n0
isotopes = atoms with extra n0
examples: 12C, 13C, and 14C
radioactive isotopes
unstable atoms that give off particles & energy as the nucleus decays

8. Electron Configuration
chemical behavior of an atom depends mostly on the # of e in the outermost shell = valence electrons

9. Energy Level of Electrons
electrons can gain and lose potential energy
gain energy  move to electron shells farther away from nucleus
lose energy  move to electron shells closer to nucleus
 the amount of potential energy held by an electron (energy level) is a function of the energy shell it occupies

10. Chemical Bonds
electrons are directly involved in the chemical reactions between atoms
atoms either share or transfer valence electrons to form chemical bonds:
Covalent
Ionic
Hydrogen
Van der Waals

11. Covalent Bonds: results from the sharing of pairs of valence electrons by 2 atoms
classified by # of pairs shared (single, double, or triple)
degree of sharing determines polarity (polar, nonpolar) – depends on the electronegativity of the atoms involved

12. Polar Covalent Bonds in Water

13. Ionic Bonds: result from a transfer of valence electrons
ions produced when electrons are transferred
anion = negatively charged ion
cation = positively charged ion
due to extreme differences in electronegativity (metals & nonmetals)
attraction between oppositely charged ions = the ionic bond
forms ionic compounds (salts)

14. Hydrogen Bonds
weak electrical attractions between the slightly negative end of one polar molecule and the slightly positive end of another polar molecule

15. van der Waals interactions
weak electrical attractions between two nonpolar molecules due to changing “hotspots” of positive & negative charge as electrons move around in the electron cloud

16. Molecular Shape & Function
molecules have characteristic sizes & shapes
molecular shape is crucial to biological function because it determines how molecules recognize & respond to each other with specificity

17. Chemical Reactions require physical contact between reactants
result from the making (synthesis rxns) & breaking (decomposition rxns) of chemical bonds
some are reversible; others are irreversible
are affected by: concentration of reactants, presence of enzymes, environmental conditions (pH, temperature)