ATOMS AND PERIODIC TABLE VOCABULARY

ATOMIC NUMBER

• 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.

ATOMIC MASS

• 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 (the mass number).

MASS NUMBER

• the total number of protons and neutrons in a nucleus.

SUBATOMIC PARTICLE

• a particle smaller than an atom

ELECTRON CLOUD

• Electron cloud is an informal way to describe an atomic orbital. Bohr talked about electrons orbiting the nucleus. Atomic orbitals also explain the patterns in the periodic table.

ENERGY LEVEL

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

VALENCE ELECTRON

• In chemistry, a valence electron is an outer shell electron that is associated with an atom.

CHEMICALLY STABLE

• Chemical stability when used in the technical sense in chemistry, means thermodynamic stability of a chemical system. Thermodynamic stability occurs when a system is in its lowest energy state, or chemical equilibrium with its environment.

CHEMICALLY REACTIVE

• Chemical reactivity is the tendency of a substance to undergo chemical changes in a system.

CONDUCTOR

• a material or device that conducts or transmits heat, electricity, or sound, especially when regarded in terms of its capacity to do this.

INSULATOR

• a substance or device that does not readily conduct electricity, heat, and sound.

SEMICONDUCTOR

• a solid substance that has a conductivity between that of an insulator and that of most metals, either due to the addition of an impurity or because of temperature effects.