Chapter 2: The Chemical Context of Life

Question 1

Valence shell

Answer 1

The outermost energy shell of an atom, containing the valence electrons involved in the chemical reactions of that atom.

Question 2

Cation

Answer 2

A positively charged ion.

Question 3

Trace elements

Answer 3

An element indispensable for life but required in extremely minute amounts.

Question 4

Ionic compounds

Answer 4

A compound resulting from the formation of an ionic bond; also called a salt.

Question 5

Atomic mass

Answer 5

The total mass of an atom, numerically equivalent to the mass in grams of 1 mole of the atom. (For an element with more than one isotope, the atomic mass is the average mass of the naturally occurring isotopes, weighted by their abundance.)

Question 6

Van der Waals interactions

Answer 6

Weak attractions between molecules or parts of molecules that result from transient local partial charges.

Question 7

Protons

Answer 7

A subatomic particle with a single positive electrical charge, with a mass of about 1.7 times 10 to the negative 24 g, found in the nucleus of an atom.

Question 8

Radioactive isotope

Answer 8

An isotope (an atomic form of a chemical element) that is unstable; the nucleus decays spontaneously, giving off detectable particles and energy.

Question 9

Reactants

Answer 9

A starting material in a chemical reaction.

Question 10

Anion

Answer 10

A negatively charged ion.

Question 11

Element

Answer 11

Any substance that cannot be broken down to any other substance by chemical reactions.

Question 12

Valence electrons

Answer 12

An electron in the outermost electron shell.

Question 13

Salts

Answer 13

A compound resulting from the formation of an ionic bond; also called an ionic compound.

Question 14

Potential energy

Answer 14

The energy that matter possesses as a result of its location or spatial arrangement (structure).

Question 15

Energy

Answer 15

The capacity to cause change, especially to do work (to move matter against an opposing force).

Question 16

Molecule

Answer 16

Two or more atoms held together by covalent bonds.

Question 17

Chemical equilibrium

Answer 17

In a chemical reaction, the state in which the rate of the forward reaction equals the rate of the reverse reaction, so that the relative concentrations of the reactants and products do not change with time.

Question 18

Ionic bond

Answer 18

A chemical bond resulting from the attraction between oppositely charged ions.

Question 19

Chemical bonds

Answer 19

An attraction between two atoms, resulting from a sharing of outer-shell electrons or the presence of opposite charges on the atoms. The bonded atoms gain complete outer electron shells.

Question 20

Ions

Answer 20

An atom or group of atoms that has gained or lost one or more electrons, thus acquiring a charge.

Question 21

Products

Answer 21

A material resulting from a chemical reaction.

Question 22

Polar covalent bond

Answer 22

A covalent bond between atoms that differ in electronegativity. The shared electrons are pulled closer to the more electronegative atom, making it slightly negative and the other atom slightly positive.

Question 23

Atomic number

Answer 23

The number of protons in the nucleus of an atom, unique for each element and designated by a subscript.

Question 24

Neutrons

Answer 24

A subatomic particle having no electrical charge (electrically neutral), with a mass of about 1.7 times 10 to the negative 24 g, found in the nucleus of an atom.

Question 25

Orbital

Answer 25

The three-dimensional space where an electron is found 90 percent of the time.

Question 26

Chemical reactions

Answer 26

The making and breaking of chemical bonds, leading to changes in the composition of matter.

Question 27

Single bond

Answer 27

A single covalent bond; the sharing of a pair of valence electrons by two atoms.

Question 28

Atom

Answer 28

The smallest unit of matter that retains the properties of an element.

Question 29

Dalton

Answer 29

A measure of mass for atoms and subatomic particles; the same as the atomic mass unit, or amu.

Question 30

Electron shells

Answer 30

An energy level of electrons at a characteristic average distance from the nucleus of an atom.

Question 31

Half-life

Answer 31

The amount of time it takes for 50 percent of a sample of a radioactive isotope to decay.

Question 32

Mass number

Answer 32

The total number of protons and neutrons in an atom’s nucleus.

Question 33

Covalent bond

Answer 33

A type of strong chemical bond in which two atoms share one or more pairs of valence electrons.

Question 34

Compound

Answer 34

A substance consisting of two or more different elements combined in a fixed ratio.

Question 35

Electronegativity

Answer 35

The attraction of a given atom for the electrons of a covalent bond.

Question 36

Hydrogen bond

Answer 36

A type of weak chemical bond that is formed when the slightly positive hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly negative atom of a polar covalent bond in another molecule or in another region of the same molecule.

Question 37

Essential elements

Answer 37

A chemical element required for an organism to survive, grow, and reproduce.

Question 38

Nonpolar covalent bond

Answer 38

A type of covalent bond in which electrons are shared equally between two atoms of similar electronegativity.

Question 39

Double bond

Answer 39

A double covalent bond; the sharing of two pairs of valence electrons by two atoms.

Question 40

Isotopes

Answer 40

One of several atomic forms of an element, each with the same number of protons but a different number of neutrons, thus differing in atomic mass.

Question 41

Valence

Answer 41

The bonding capacity of a given atom; the number of covalent bonds that an atom can form, which usually equals the number of unpaired electrons in its outermost (valence) shell.

Question 42

Electrons

Answer 42

A subatomic particle with a single negative electrical charge and a mass about 1 two-thousandths that of a neutron or proton. One or more electrons move around the nucleus of an atom.

Question 43

Radiometric dating

Answer 43

A method for determining the absolute age of rocks and fossils, based on the half-life of radioactive isotopes.

Question 44

Matter

Answer 44

Anything that takes up space and has mass.

Question 45

Atomic nucleus

Answer 45

An atom’s dense central core, containing protons and neutrons.