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Chapter 2: The Chemical Context of Life vocabulary Biology, 8th edition, Campbell & Reece


Anything that takes up space and has mass.


A substance that cannot be broken down to other substances by chemical reactions.


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

trace element

An element indispensable for life but required in extremely minute amounts. Ex: in humans are boron and iodine

carbon, hydrogen, nitrogen, oxygen

96% of all the matter in living organisms is composed of what four elements? (alphabetical order)


How many elements are essential for life?


How many elements occur in nature?


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

subatomic particles

protons, neutrons and electrons


A subatomic particle having no electrical charge (electrically neutral), with a mass of about 1.7x10^-24 g, found in the nucleus of an atom.


A subatomic particle with a single positive electrical charge, with a mass of about 1.7x10^-24 g, found in the nucleus of an atom.


A subatomic particle with a single negative electrical charge and a mass about 1/2,000 that of a neutron or proton. One or more electrons move around the nucleus of an atom.


Which type of subatomic particle must be the same in number for all atoms of the same element?


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

atomic nucleus

The center of an atom tightly packed with neutrons and protons.

atomic number

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

mass number

The sum of protons plus neutrons in the nucleus of an atom and designated by a superscript to the left of the symbol.

atomic mass

The total mass of an atom, including electrons, which is the mass in grams of 1 mole of the atom.


One of several different atomic forms of an element that have more neutrons, and therefore a greater mass, than other atoms of the same element.

radioactive isotope

An isotope (an atomic form of a chemical element) that is unstable; the nucleus decays spontaneously, giving off detectable particles and energy. When the decay leads to a change in the number of protons, it transforms the atom to the atom of a different element.

nonradioactive isotope

An isotope (an atomic form of a chemical element) that reacts only when combined with atoms of another element

radioactive isotope

Uses of these include: 1) tracers to follow atoms through metabolism or other chemical processes within an organism; 2) used as tracers in diagnostic methods by injecting them into blood and measuring amount of tracer later excreted; 3) used to determine date/age of fossils.


Which subatomic particles are directly involved in the chemical reactions between atoms?

farther away

Which has more potential energy, an electron close to the nucleus or one farther away?

releases energy

If an electron falls from a higher shell to a lower one, does the electron absorb energy or release energy?


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

potential energy

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

electron shell

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

first shell

Can hold up two electrons.

valence electron

An electron in the outermost electron shell.

valence shell

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


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


How an atom behaves chemically mostly depends on the number of electrons in the atom's ____________ shell.

chemical bond

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.

covalent bond

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


Two or more atoms held together by covalent bonds.

ionic bond

The attraction that exists between opposing (positive and negative) charges within the atom.

single covalent bond

Type of bond that exists when two atoms share a pair of electrons; weakest form of this type of bond

double covalent bond

Type of bond that exists when two atoms share two pairs of electrons; second strongest form of this type of bond.

triple covalent bond

Type of bond that exists when two atoms share three pairs of electrons; strongest form of this type of bond.

structural formula

A type of molecular notation in which the constituent atoms are joined by lines representing covalent bonds.

molecular formula

A type of molecular notation representing the quantity of constituent atoms, but not the nature of the bonds that join them.


The bonding capacity of a given atom; generally equal to the number of unpaired electrons required to complete the atom's outermost (valence) shell.


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

nonpolar covalent bond

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

polar covalent bond

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.


An atom that has gained or lost electrons, thus is electrically charged.


Electron donor, an ion with a positive charge, produced by the loss of one or more electrons. It is oxidized.


Electron acceptor, a negatively charged ion.

ionic bond

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

ionic compound (salt)

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

hydrogen bond

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.

chemical reaction

A process leading to chemical changes in matter; involves the making and/or breaking of chemical bonds.


A starting material in a chemical reaction.


An ending material in chemical reaction.

van der Waals interaction

Weak attractions between molecules or parts of molecules that are brought about by localized charge fluctuations.

chemical equilibrium

The point at which the forward and reverse reactions in a chemical reaction offset each other, thus diminishing their effects on the reactants involved


The shape of a molecule that results from 4 bonded atoms.

bent, pyramid

The shapes of a molecule that results from 3 bonded atoms.


The shape of molecule that results from 2 bonded atoms.

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