Chemical symbols
An abbreviation that represents the name of an element.
Periodic table
An arrangement of elements by increasing atomic number such that elements having similar chemical behavior are grouped in vertical columns.
Period
A horizontal row of elements in the periodic table.
Group
A vertical column in the periodic table that contains elements having similar physical and chemical properties.
Representative elements
An element in the first two columns on the left of the periodic table and the last six columns on the right that has a group number of 1A through 8A or 1, 2, and 13 through 18.
Group numbers
A number that appears at the top of each vertical column (group) in the periodic table and indicates the number of electrons in the outermost energy level.
Transition Elements
An element in the center of the periodic table that is designated with the letter "B" or the group number of 3 through 12.
Alkali metal
An element in Group 1A (1), except hydrogen, that is a soft, shiny metal with one electron in its outermost energy level.
Alkaline earth metals
An element in Group 2A (2) that has two electrons in its outermost energy level.
Halogens
An element in Group 7A (17) - fluorine, chlorine, bromine, iodine, and astatine - that has seven electrons in its outermost energy level.
Noble gases
An element in Group 8A (18) of the periodic table, generally, unreactive and seldom found in combination with other elements, that has eight electrons (helium has two electrons) in its outermost energy level.
Metals
An element that is shiny, malleable, ductile, and a good conductor of heat and electricity. The metals are located to the left of the heavy zigzag line on the periodic table.
Nonmetals
An element with little or no luster that is a poor conductor of heat and electricity. The nonmetals are located to the right of the heavy zigzag line on the periodic table.
Metalloids
Elements with properties of both metals and nonmetals located along the heavy zigzag line on the periodic table.
Atom
The smallest particle of an element that retains the characteristics of the element.
Subatomic particles
A particle within an atom; protons, neutrons, and electrons are subatomic particles.
Electrons
A negatively charged subatomic particle having a minute mass that is usually ignored in mass calculations; its symbol is e^-
Protons
A positively charged subatomic particle having a mass of about 1 amu and found in the nucleus of an atom; its symbol is p or p^+
Nucleus
The compact, extremely dense center of an atom, containing the protons and neutrons of the atom.
Neutron
A neutral subatomic particle having a mass of about 1 amu and found in the nucleus of an atom; its symbol is n or N^0
Atomic mass unit (amu)
A small mass unit used to describe the mass of extremely small particles such as atoms and subatomic particles; 1 amu is equal to one-twelfth the mass of a ^12/6 C atom.
Atomic number
A number that is equal to the number of protons in an atom.
Mass number
The total number of protons and neutrons in the nucleus of an atom.
Isotopes
An atom that differs only in mass number from another atom of the same element. Isotopes have the same atomic number (number of protons) but different numbers of neutrons.
Atomic symbol
An abbreviation that represents the name of an element.
Atomic mass
The weighed average mass of all the naturally occurring isotopes of an element.
Energy level
A group of electrons with similar energy.
Sublevels
A group of orbitals of equal energy within principal energy levels. The number of sublevels in each energy level is the same as the principal quantum number (n).
Orbital
The region around the nucleus where electrons of a certain energy are more likely to be found. The s oribitals are spherical the p orbitals have two lobes.
Valence electrons
Electrons in the highest energy level of an atom.
Electron-dot symbol
The representation of an atom that shows valence electrons as dots around the symbol of the element.
Ionization energy
The energy needed to remove the least tightly bound electron from the outermost energy level of an atom.
Metallic character
A measure of how easily an element loses a valence electron.