AP BIO CH 2

anion

anion

A negatively charged ion.

atom

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

atomic mass

The total mass of an atom, which is the mass in grams of one mole of the atom.

atomic nucleus

An atom's central core, containing protons and neutrons.

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.

cation

An ion with a positive charge, produced by the loss of one or more electrons.

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.

chemical equilibrium

In a reversible chemical reaction, the point at which the rate of the forward reaction equals the rate of the reverse reaction.

chemical reaction

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

compound

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

covalent bond

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

dalton

A measure of mass for atoms and subatomic particles.

electron

A subatomic particle with a single negative charge. One or more electrons move around the nucleus of an atom.

electron shell

An energy level represented as the distance of an electron from the nucleus of an atom.

electronegativity

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

element

Any substance that cannot be broken down to any other substance.

energy

The capacity to do work (to move matter against an opposing force).

energy level

Any of several different states of potential energy for electrons in an atom.

hydrogen bond

A type of weak chemical bond 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.

ion

An atom that has gained or lost electrons, thus acquiring a charge.

ionic bond

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

ionic compound

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

isotope

One of several atomic forms of an element, each containing a different number of neutrons and thus differing in atomic mass.

mass number

The sum of the number of protons and neutrons in an atom's nucleus.

matter

Anything that takes up space and has mass.

molecular formula

A type of molecular notation indicating only the quantity of the constituent atoms.

molecule

Two or more atoms held together by covalent bonds.

neutron

An electrically neutral particle (a particle having no electrical charge), found in the nucleus of an atom.

nonpolar covalent bond

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

orbital

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

periodic table of the elements

A chart of the chemical elements, arranged in three rows, corresponding to the number of electron shells in their atoms.

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.

potential energy

The energy stored by matter as a result of its location or spatial arrangement.

product

An ending material in a chemical reaction.

proton

A subatomic particle with a single positive electrical charge, found in the nucleus of an atom.

radioactive isotope

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

reactant

A starting material in a chemical reaction.

salt

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

structural formula

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

trace element

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

valence

The bonding capacity of an atom, generally equal to the number of unpaired electrons in the atom's outermost shell.

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.

van der Waals interactions

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