The dense, positively charged mass located in the center of an atom
Nucleus
A positively charged subatomic particle that is found in the nucleus of an atom
Proton
A negatively charged subatomic particle that is found in the space outside the nucleus of an atom
Electron
A neutral subatomic particle that is found in the nucleus of an atom
Neutron
A unique number for each element that equals the number of protons in an atom of that element
Atomic number
The sum of the number of protons and neutrons in the nucleus of an atom
Mass number
Atoms of a given element that have different numbers of neutrons and different mass numbers
Isotopes
The possible energies that electrons in an atom can have
Energy levels
A visual model of the most likely locations for the electrons in an atom
Electron cloud
A region of space around the nucleus where an electron is likely to be found
Orbital
The arrangement of electrons in the orbitals of an atom
Electron configuration
A state in which all the electrons in an atom have the lowest possible energies
Ground state
An arrangement of elements in columns, based on a set of properties that repeat from row to row
Periodic table
A row in a periodic table of elements
Period
A column of elements in a periodic table
Group
The pattern of repeating properties displayed by elements in the elements in the periodic table
Periodic law
One twelfth the mass of a carbon-12 atom
Atomic mass unit
Elements that are good conductors of heat and electric current
Metals
Elements that form a bridge between elements on the left and right sides of the periodic table
Transition metals
Elements that are poor conductors of heat and electric current
Nonmetals
Elements with properties that fall between those of metals and nonmetals
Metalloids
An electron that is in the highest occupied energy level of an atom
Valence electron
The elements in group 1a of the periodic table, not including hydrogen
Alkali Metals
The elements in group 2a of the periodic table
Alkaline earth metals
The elements in group 7a of the periodic table
Halogens
The elements in group 8a of the periodic table
Noble gases