ATOMS AND PERIODIC TABLE

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) or to the average number allowing for the relative abundances of different isotopes.

MASS NUMBER

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

SUBATOMIC PARTICLE

• a particle smaller than an atom or a cluster of such particles

ELECTRON CLOUD

• is an informal term in physics. It is used to describe where electrons are when they go around the nucleus of an atom.

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

• a valence electron is an outer shell electron that is associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed

CHEMICALLY STABLE

• Chemical stability when used in the technical sense in chemistry, means thermodynamic stability of a chemical system.

CHEMICALLY REACTIVE

• Reactivity then refers to the rate at which a chemical substance tends to undergo a chemical reaction in time. In pure compounds, reactivity is regulated by the physical properties of the sample.

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SEMICONDUCTOR

• a substance, as silicon or germanium, with electrical conductivity intermediate between that of an insulator and a conductor