Molecular Geometry Vocabulary
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Aufbau principle – the configuration (order of filling) of the s, p, d, and f orbitals; electrons fill the
lowest energy levels first
Covalent bond – a bond in which electrons are shared, equally or unequally
Electron affinity – energy released when an electron is added to an atom to form an ion
Electron orbitals (s, p, d, and f) – the different energy levels filled by electrons within an atom
Hund’s rule – electrons fill empty orbitals before they pair up
Ion – a negatively or positively charged atom (monatomic) or group of atoms (polyatomic)
Ionic bond – a bond in which one or more electrons are given by one atom to another
Lewis dot structure – an atomic symbol with dots showing valence electrons
Metallic bond – a bond in which the valence electrons are shared among all of the atoms in the
metal
Molecular geometry – the 3D shape of a covalent molecule, as determined by shared and
unshared electrons
Octet rule – elements, other than transition metals, that tend to react so that each atom has eight
electrons in its outer (valence) shell (e.g., orbitals are full)
Oxidation number – for atoms of pure elements, the oxidation number is zero; for monatomic
ions, it is the charge on the ion; in polyatomic ions, the oxidation numbers of the component
atoms add up to the charge on the ion; in a neutral molecule, the oxidation numbers add up to
zero
Pauli exclusion principle – electrons in the same orbital, and the value must have opposite
spins
Polar and nonpolar molecules – because of differences in electronegativity, different types
of atoms in covalent molecules do not share electrons equally; in a 3D symmetrical molecule, the
unequal sharing cancels out, and the molecule is nonpolar; in a 3D nonsymmetrical molecule, the
unequal sharing does NOT cancel out, so that there is partial positive area and a partial negative
area
VSEPR (Valence Shell Electron Pair Repulsion) Theory – unshared electron pairs of atoms in
covalent molecules repel each other; thus, the shape of the molecule will tend to minimize the net
repulsions
1
Aufbau
principle
A
Electrons fill an empty
orbital before they pair
up
2
Hund’s Rule
Molecular
Geometry
VSEPR
Theory
Polar
molecule
B
A negatively (-) charged ion
C
The energy released when an atom gains an
electron and forms an anion
D
Electrons fill the lowest energy orbitals (spdf)
first
E
The three-dimensional (3D) shape
of a covalent molecule
6
Nonpolar
molecule
F
7
Electron
Affinity
G
8
Anion
Cation
Dipole
Moment
H
Unshared electron pairs in a
molecule repel each other, and
these repulsions create a 3D
shape for the molecule
Electrons pair up in the same orbital,
and these electrons spin in opposite
directions
A positively (+) charged ion
Pauli
exclusion
principle
K
3
4
5
9
10
11
I
A molecule that has no partial charges
J
A molecule that shares
electrons unevenly and has
partial charges at opposite
ends
A vector arrow that describes
the size and direction of
partial charge differences in a
polar molecule