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anything that takes up space and mass


substance that cannot be broken down to other substances by chemical reaction


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

trace elements

an element indispensable for life but required in extremely minimum amounts


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


the particles of the nucleus that have no charge


positively charged particles in the nucleus of an atom


negatively charged particles found outside the nucleus

atomic nucleus

atom's dense central core, containing protons and neutrons


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

atomic number

the number of protons in the nucleus of an atom

mass number

the sum of the number of neutrons and protons in an atomic nucleus

atomic mass

total mass of an atom, which is the mass in grams of 1 mole of the atom


atoms of the same element that have different numbers of neutrons

radioactive isotope

isotope that is unstable; nucleus decays spontaneously, giving off detectable partices and energy


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

potential energy

emergy that matter possesses as a result of its location or spatial arrangement (structure)

electron shells

energy level of electrons at a characteristic avg. distance from nucleus of atom

valence electrons

The electrons in the outermost shell (main energy level) of an atom; these are the electrons involved in forming bonds.

valence shell

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


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

chemical bonds

an attraction between two atoms resulting from the sharing of outer-shell electrons or the presence of opposite charges


two or more atoms held together by covalent bonds

single bond

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

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.

double bond

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


the bonding capacity of a given atom; usually equals 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 orgroup of atoms that has gained or lost one more electrons; thus acquiring a charge


a positively charged ion


a negatively charged ion

ionic bond

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

ionic compounds or salts

A compound resulting from the formation of an ionic bond.

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 equilibrium

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.

covalent bond

sharing of a pair of valence electrons by two atoms.

chemical reactions

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


the starting materials in a chemical reaction


Ending materials in a chemical reaction.

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