AP Biology, Chapter 2
The Chemical Context of Life

Summary
Introduction

CHEMICAL ELEMENTS AND COMPOUNDS
	Matter consists of chemical elements in pure form and in combinations called 
		compounds
		1. Distinguish element and compound.
			a. Elements: simplest chemically distinguishable units of matter
			b. Compounds: combinations of elements
	Life requires about 25 chemical elements
		2. Describe the elemental composition (up to 99% total) of a representative organism.
			a. CHON = 96%
			b. CaPKSNaClMg = 3.7%

ATOMS AND MOLECULES
	Atomic structure determines the behavior of an element
		3. Describe the structure of an atom.
			a. Protons: big and positive in the nucleus 
			b. Neutrons:  big and neutral in the nucleus 
			c. Electrons: small and negative in orbitals outside the nucleus 
		4. Define and distinguish atomic number, mass number, atomic weight and valence.
			a. Atomic number = # of protons; unique for an element
			b. Mass number = # protons + # neutrons; isotopes of elements vary
			c. Atomic weight
				i. Mass of one mole of a natural sample of an element
				ii. Weighted average of its naturally occurring isotopes
		5. Given the atomic number and mass number of an atom, how do you determine the 			number of its neutrons?
			a. At. # = # of protons
			b. Mass # = # protons + # neutrons
			c. Subtract
		6. How are radioactive isotopes useful in the study of biological processes?
			a. Dating biological materials and the layers they are embedded in
			b. Tracers for measuring the rates of chemical movement in the body
			c. Labeled atoms allow reconstruction of biochemical pathways
		7. Explain how its electron configuration influences the chemical behavior of an atom.
			a. Matter has a tendency to move to the lowest possible energy state
			b. Atoms react in order to fill their outermost electron shells
				i. Two electrons fill the inner shell of H and He
				ii. Eight fill the second and third shells
				iii. H needs 1, O needs 2, N needs 3
	Atoms combine by chemical bonding to form molecules
		8. Distinguish nonpolar covalent, polar covalent, and ionic bonds.
			a. Nonpolar covalent
				i. Equal or near equal sharing of electrons between atoms
				ii. Between atoms of equal or similar electronegativity
			b. Polar covalent: unequal sharing, unequal electronegativity
			c. Ionic: attraction by opposite charge from the transfer of electrons
				i. Anion is the negative ion involves
				ii. Cation is the positive
	Weak chemical bonds play important roles in the chemistry of life
		9. Explain why weak bonds are important to living organisms.
			a. Weak bonds may form briefly
			b. Easily reversible
			c. Allows complex reversible interaction of large molecules
		10. Describe and compare hydrogen bonds and van der Waals interactions.
			a. Hydrogen bonds
				i H involved in polar covalent is positive
				ii. Attracted to O (negative) involved in other polar bonds
			b. van der Waals
				i. Electron motions allow temporary positive and negative regions
				ii. Opposite attractions allow sticking
	A molecules biological function is related to its shape
		11. Explain how a molecule's shape influences its biological function.
			a. Shape = geometry of orbitals on the surface
			b. Orbitals must collide at the right angle for a reaction to begin
			c. Large biological molecules have specific shapes that expose/protect reactive 
			orbitals
	Chemical reactions make and break chemical bonds
		12. Write the chemical reaction that summarizes the process of photosynthesis, noting 			the reactants and products.
			a. Reactants: 6CO2 and 6H2O
			b.  (react to form)
			c. Products: C6H12O6 + 6O2
		13. Describe how the relative concentrations of reactants and products affect a chemical 
		reaction.
			a. Excess reactants allows more frequent collisions so products form
			b. As the reactants disappear those collisions become less frequent
			c. Excess products allows collisions with enough energy for the reverse reaction 
			to occur