AP Biology Chapter 2 Vocabulary - The Chemical Context of Life

matter

anything that takes up space and has mass

element

any substance that cannot be broken down to any other substance

compound

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

trace elements

an element indispensable for life but required in extremely minute amounts

atom

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

neutrons

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

protons

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

electrons

a subatomic particle with a single negative charge; one or more electrons move around the nucleus of an atom

atomic nucleus

an atom's central core, containing protons and neutrons

dalton

a measure of mass for atoms and subatomic particles

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

atomic mass

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

isotopes

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

radioactive isotope

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

energy

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

potential energy

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

energy levels

any of several different states of potential energy for electrons in an atom

electron shells

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

valence electrons

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

orbital

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

chemical bonds

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

molecule

two or more atoms held together by covalent bonds

single bond

a pair of shared electrons

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 indicating only the quantity of the constituent atoms

double bond

molecules that share two pairs of valence electrons

valence

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

electronegativity

the attraction of an 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

ion

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

cation

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

anion

an negatively charged ion

ionic bond

a chemical bond resulting from the attraction between oppositely charged ions

ionic compound (salts)

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

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

van der Waals interactions

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

chemical reactions

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

reactants

a starting material in a chemical reaction

products

an ending material in a chemical reaction

chemical equilibrium

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