Chapter 4 Atoms – Key Terms
5.1 History of Atomic Development
nucleus - the center of an atom; made up of protons and neutrons
electron - a tiny negatively charged subatomic particle moving around outside the nucleus of an
atom
proton - a positively charged subatomic particle in the nucleus of an atom
neutron - a neutral subatomic particle in the nucleus of an atom
ion - an atom or group of atoms that has lost or gained one or more electrons and therefore has a
net electric charge
ionization - the process of adding electrons to or removing electrons from an atom or group of
atoms
anion - an ion with a negative charge
cation - an ion with a positive charge
5.2 Atomic Structure
atomic number - the number of protons in the nucleus of an atom
average atomic mass - the weighted average of the masses of all naturally occurring isotopes of
an element
mass number - the total number of protons and neutrons in the nucleus of an atom
isotopes - any atoms having the same number of protons but different numbers of neutrons
atomic mass unit (amu) - a quantity equal to one-twelfth the mass of a carbon-12 atom (84)
mole - the SI base unit that describes the amount of a substance
molar mass - the mass in grams of 1 mol of a substance
Avogadro’s constant - the number of particles in 1 mol; equals 6.0223 1023/mol
5.3 Modern Atomic Theory
energy level - any of the possible energies an electron may have in an atom
orbital - a region in an atom where there is a high probability of finding electrons
valence electron - an electron in the outermost energy level of an atom
photon – a unit or quantum of light