Alkali Metal
any group IA (1) element except hydrogen; Li, Na, K, Rb, Cs, and Fr are alkali metals.
Alkaline Earth Metal
any group IIA (2) element; Be, Mg, Ca, Sr, Ba, and Ra.
Anion
a negatively charged ion, such as the chloride (CI-) or nitrate ion (NO3-).
Atomic Mass Unit (AMU)
the basic unit of atoms and molecules; exactly one-twelfth the mass of one 12C atom; 1 amu = 1.6606 X 10-24 g.
Atomic Number
the number of protons in the nucleus of an atom of a given element.
Cation
a positively charged ion, such as the sodium ion (Ns+); an ion that contains fewer electrons than protons.
Dalton's Atomic Theory
the first widely accepted theory that describes matter as being composed of atoms; published in 1808.
Diatomic Molecule
a neutral particle consisting of two bound atoms.
Electron
a negatively charged subatomic particle.
Family
a vertical column of related elements in the periodic table; another name for group.
Group
a vertical column of related elements in the periodic table; another name for group.
Halogen
any group VHA (17) element; the nonmetals F, Cl, Br, I, and At are halogens.
Inner-transition metal
an element that is a lanthanide (atomic numbers 58 to 71) or an actinide (atomic numbers 90 to 103).
Ion
an atom or molecule bearing an electrical charge.
Isotope
an atom of an element with a specific number of neutrons.
Isotope Symbol
an element symbol with the atomic number (Z) as the left subscript and a mass number (A) as the left superscript.
Law of Conservation of Mass
a law stating that the mass of the substances produced in a chemical reaction equals the mass of the substances that reacted.
Law of Definite Proportions
a law stating that all samples of the same pure compound will always contain the same proportions by mass of the component elements.
Main-group Element
a member of one of the A groups of elements in the periodic table; also called a representative.
Mass Number
the sum of the number of protons and the number of neutrons in the nucleus of an atom or ion.
Mettaloid
an element that has properties intermediate between those of metals and nonmetals; also called semimetal; an element with physical properties resembling a metal but chemical reactivity like that of a nonmetal.
Neutron
an electrically neutral subatomic particle.
Neutron Number
the number of neutrons in the nucleus of an atom.
Noble Gas
any group VIIIA (18) element ; He, Ne, Ar, Kr, Xe, and Rn are noble gases.
Nucleus
the central core of an atom which contains the protons and neutrons; contributes most of the mass of the atom.
Period
a horizontal row of elements in the periodic table.
Periodic Table
an arrangement of all the known elements by increasing atomic number and arranged in columns and rows to emphasize periodic properties.
Proton
a positively charged subatomic particle.
Relative Atomic Mass
the average mass of an atom of an element, taking into account the masses and abundance of all the naturally occurring isotopes.
Subatomic Particle
a particle found within an atom.
Transition Metal
a member of one of the B groups of elements in the periodic table.