CHAPTER 2

Question 1

atoms

Answer 1

matter is composed of them; electrically neutral

Question 2

electrons

Answer 2

negligible mass; negative charge

Question 3

proton

Answer 3

have mass; positive charge (in nucleus)

Question 4

neutrons

Answer 4

have mass; no charge (in nucleus)

Question 5

dalton (Da)

Answer 5

mass of one proton or neutron; 1.7 x 10^-24 grams

Question 6

element

Answer 6

fundamental substance containing only one kind of atom

Question 7

atomic number

Answer 7

identifies an element; number of protons

Question 8

mass number

Answer 8

protons + neutrons

Question 9

isotopes

Answer 9

forms of an element with different numbers of neutrons, and thus different mass number
EXAMPLES: HYDROGEN (1 proton, 0 neutrons; DEUTERIUM 1 proton, 1 neutron; TRITIUM 1 proton, 2 neutrons)

Question 10

radioisotopes

Answer 10

give off energy in the form of alpha, beta, and gamma radiation from nucleus (radioactive decay); atom is transformed, sometimes to a different element; can be incorporated into molecules as a tag or label

Question 11

molecule

Answer 11

stable association of atoms

Question 12

orbital

Answer 12

region where an electron is found at least 90% of the time

Question 13

electron shells

Answer 13

sequence of orbitals; energy levels
FIRST - 1 orbital or 2 electrons
SECOND - 4 orbitals or 8 electrons
ADDITIONAL - 4 orbitals or 8 electrons
; the farther a shell from the nucleus, the higher energy level of electrons in that shell

Question 14

valence shell

Answer 14

outermost electron shell; determines how the atom behaves; if full, atom is stable

Question 15

octet rule

Answer 15

tendency of atoms to form stable molecules resulting in full valence shells

Question 16

chemical bond

Answer 16

attractive force that links atoms together to form molecules

Question 17

covalent bonds

Answer 17

atoms share one or more pairs of electrons so the outer shells are filled; each atom contributes one member of each electron pair; very strong; length, angle, and direction of bonds between any two elements are always the same; molecular shape can change as atoms rotate around a covalent bond

Question 18

compound

Answer 18

pure substance made up of two or more different elements bonded together in a fixed ratio

Question 19

molecular weight

Answer 19

sum of atomic weights of all atoms in the molecule

Question 20

electronegativity

Answer 20

attractive force that an atomic nucleus exerts on electrons; depends on number of protons and distance between nucleus and electrons

Question 21

nonpolar covalent bond

Answer 21

electrons are shared equally (atoms have similar electronegativity)

Question 22

polar covalent bond

Answer 22

one atom has greater electronegativity, so electrons are drawn more to that nucleus

Question 23

ionic bonds

Answer 23

complete transfer of electrons because of higher difference of electronegativity; two ions form with full outer shells

Question 24

ions

Answer 24

electrically charged particles formed when atoms lose or gain one or more electrons (CATIONS - positive; ANIONS - negative); can interact with polar molecules

Question 25

complex ions

Answer 25

groups of covalently bonded atoms that carry a charge (e.g. NH4+ and SO4-2)

Question 26

ionic bonds

Answer 26

formed by electrical attraction of positive and negative ions; in solids they are strong because ions are close together but in water they are far apart

Question 27

hydrogen bonds

Answer 27

attraction between the - end of one molecule and the + hydrogen end of another molecule; weaker than ionic and covalent bonds; many in a large molecule can be strong and play an important role in the structure of DNA and proteins

Question 28

hydrophilic

Answer 28

polar molecules that form hydrogen bonds with water

Question 29

hydrophobic

Answer 29

nonpolar molecules, such as hydrocarbons

Question 30

van der Waals forces

Answer 30

attraction between nonpolar molecules that are close together, brief and weak but can be substantial when summed over a large molecule; important when hydrophobic regions of molecules (enzyme and substrate) come together

Question 31

chemical reactions

Answer 31

occur when atoms collide with enough energy to combine or change their bonding patterns; matter and energy are neither created nor destroyed; therefore, they must be balanced

Question 32

oxidation-reduction (redox) reaction

Answer 32

electrons are transferred between two molecules (OXIDIZING AGENT - gains electrons; becomes reduced REDUCING AGENT - loses electrons; becomes oxidized)

Question 33

energy

Answer 33

capacity to do work; capacity for change; changes form during chemical reactions

Question 34

Why does water have unusual properties?

Answer 34

polarity and ability to form hydrogen bonds

Question 35

Why does ice float?

Answer 35

each molecule of ice is hydrogen-bonded to four other molecules and the space between them make it less dense than water

Question 36

specific heat

Answer 36

amount of energy needed to raise the temperature of 1 gram of a substance by 1 degree Celsius; water has it high

Question 37

heat of vaporization

Answer 37

heat energy required to change liquid to gaseous state (evaporation); water has it high

Question 38

cohesion

Answer 38

hydrogen bonds between water molecules cause them to stick together; helps water move through plants; results in surface tension

Question 39

adhesion

Answer 39

attraction of water molecules to other molecules of a different type

Question 40

solution

Answer 40

substance (solute) dissolved in a liquid (solvent); dissolved molecules don't lose their identity and properties; therefore, they can still react

Question 41

analyses

Answer 41

qualitative - identifying the substance quantitative - measuring concentration or amount of substance

Question 42

mole

Answer 42

amount of a substance (in grams) numerically equal to its molecular weight (e.g. 1 mole of Na+ = 23 g)

Question 43

Avogadro's number

Answer 43

number of molecules in 1 mole (6.02 x 10^23 molecules); constant

Question 44

molar (1 M) solution

Answer 44

1 mole / 1 liter

Question 45

acids

Answer 45

release hydrogen ions (H+) in water; if H+ concentration is increased, the solution is acidic; H+ ions can attach to other molecules and change their properties

Question 46

weak acids

Answer 46

not all the acid molecules dissociate into ions (e.g., acetic acid CH3COOH)

Question 47

strong acids

Answer 47

dissociate completely (e.g., hydrochloric acid HCl)

Question 48

bases

Answer 48

accept H+ ions

Question 49

strong base

Answer 49

NaOH

Question 50

weak base

Answer 50

bicarbonate ion (HCO3-), ammonia (NH3), and compounds with amino groups (NH2)

Question 51

acid-base reactions

Answer 51

may be reversible (ionization of strong acids and bases is irreversible; ionization of weak acids and bases is somewhat reversible)

Question 52

What is the connection with acids, bases, and water?

Answer 52

water acts as both a weak acid and weak base; has a slight tendency to ionize (important because of abundance of water in living systems and the reactive nature of H+ ions)

Question 53

pH

Answer 53

negative log of the molar concentration of free H+ ions in the solution, water = 7; the lower it is, the higher H+ concentration or greater acidity; influences rates of biological reactions; can change the 3-D structure of biological molecules which impacts function; organisms use many mechanisms to minimize its change in their cells and tissues

Question 54

buffer

Answer 54

weak acid and its corresponding base (e.g., carbonic acid (H2CO3) and bicarbonate ion (HCO3-)); help maintain constant pH; illustrate the law of mass action

Question 55

law of mass action

Answer 55

addition of a reactant on one side of a reversible system drives the system in the direction that uses up the compound; addition of an acid drives the reaction in one direction; addition of a base drives the reaction in the other direction