Ch 2: Atomic Structure and Interatomic Bonding

atomic number (Z)

A measure of atomic mass; 1/12 of the mass of an atom of 12C

atomic mass unit (amu)

A measure of atomic mass; 1/12 of the mass of an atom of 12C

atomic weight (A)

The weighted average of the atomic masses of an atom's naturally occurring isotopes. It may be expressed in terms of atomic mass units (on an atomic basis), or the mass per mole of atoms.

isotope

Atoms of the same element that have different atomic masses.

mole

The quantity of a substance corresponding to 6.022 × 10^23 atoms or molecules.

Pauli exclusion principle

The postulate that for an individual atom, at most two electrons, which necessarily have opposite spins, can occupy the same state.

electron state

One of a set of discrete, quantized energies that are allowed for electrons. In the atomic case each state is specified by four quantum numbers.

electron configuration

For an atom, the manner in which possible electron states are filled with electrons.

ground state

A normally filled electron energy state from which an electron excitation may occur.

bonding energy

The energy required to separate two atoms that are chemically bonded to each other. It may be expressed on a per-atom basis or per mole of atoms.

coulombic force

A force between charged particles such as ions; the force is attractive when the particles are of opposite charge.

primary bond

Interatomic bonds that are relatively strong and for which bonding energies are relatively large. Primary bonding types are ionic, covalent, and metallic.

secondary bond

Interatomic and intermolecular bonds that are relatively weak and for which bonding energies are relatively small. Normally, atomic or molecular dipoles are involved. Examples of secondary bonding types are van der Waals forces and hydrogen bonding.

ionic bond

A coulombic interatomic bond that exists between two adjacent and oppositely charged ions.

covalent bond

A primary interatomic bond that is formed by the sharing of electrons between neighboring atoms.

metallic bond

A primary interatomic bond involving the nondirectional sharing of nonlocalized valence electrons ("sea of electrons") that are mutually shared by all the atoms in the metallic solid.

van der Waals bond

A secondary interatomic bond between adjacent molecular dipoles that may be permanent or induced.

hydrogen bond

A strong secondary interatomic bond that exists between a bound hydrogen atom (its unscreened proton) and the electrons of adjacent atoms (specifically oxygen, nitrogen, or fluorine).

electronegative

For an atom, having a tendency to accept valence electrons. Also used to describe nonmetallic elements.

electropositive

For an atom, having a tendency to release valence electrons. Also, a term used to describe metallic elements.

dipole (electric)

A pair of equal and opposite electrical charges separated by a small distance.

polar molecule

A molecule in which there exists a permanent electric dipole moment by virtue of the asymmetrical distribution of positively and negatively charged regions.

valence electron

The electrons in the outermost occupied electron shell, which participate in interatomic bonding.