Chapter 5

The base unit of a chemical element

A stable subatomic particle with a charge of negative electricity, found in all atoms.

A particle smaller than an atom

The positively charged central core of an atom, consisting of protons and neutrons and containing nearly all its mass.

A stable subatomic particle occurring in all atomic nuclei, with a positive electric charge equal in magnitude to that of an electron, but of opposite sign.

A subatomic particle of about the same mass as a proton but without an electric charge, present in all atomic nuclei except those of ordinary hydrogen

The fixed amount of energy that a system described by quantum mechanics, such as a molecule, atom, electron, or nucleus, can have.

The number of protons in the nucleus of an atom, which determines the chemical properties of an element and its place in the periodic table.

The total number of protons and neutrons in a nucleus.

Each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element.

Depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus.

the mass of an atom of a chemical element expressed in atomic mass units. It is approximately equivalent to the number of protons and neutrons in the atom.

A table of the chemical elements arranged in order of atomic number.

A solid material that is typically hard, shiny, malleable, fusible, and ductile, with good electrical and thermal conductivity.

An element or substance that is not a metal.

An element whose properties are intermediate between those of metals and solid nonmetals. They are electrical semiconductors.

A period is the name given to a horizontal row of the periodic table.

A group is the name given to a vertical column of the periodic table.

Any of the elements lithium, sodium, potassium, rubidium, cesium, and francium, occupying Group IA (1) of the periodic table. They are very reactive, electropositive, monovalent metals forming strongly alkaline hydroxides.

The alkaline earth metals are beryllium, magnesium, calcium, strontium, barium, and radium. This group lies in the s-block of the periodic table.

Any of the elements fluorine, chlorine, bromine, iodine, and astatine, occupying group 17 of the periodic table. They are reactive nonmetallic elements that form strongly acidic compounds with hydrogen, from which simple salts can be made.

Any of the gaseous elements helium, neon, argon, krypton, xenon, and radon, occupying 18 of the periodic table. They were long believed to be totally unreactive but compounds of xenon, krypton, and radon are now known.

A valence electron is an electron that is associated with an atom, and that can participate in the formation of a chemical bond; in a single covalent bond, both atoms in the bond contribute one valence electron in order to form a shared pair.