Molecular Geometry

bond order

the number of bonds between atoms: 1 for a single bond, 2 for a double bond, and 3 for a triple bond

bond energy

the energy needed to break 1 mole of a covalent bond in a molecule or in a polyatomic ion in the gas phase

bond angle

the angle (in degrees) defined by lines joining the centers of two atoms to the center of a third atom to which they are chemically bonded

valence-shell electron-pair repulsion (VSEPR) theory

a model predicting that the arrangement of valence electron pairs around a central atom minimizes their mutual repulsion to produce the lowest-energy orientations

electron-pair geometry

the three-dimensional arrangement of bonding pairs and lone pairs of electrons about a central atom

molecular geometry

the three-dimensional arrangement of the atoms in a molecule

steric number (SN)

the sum of both the number of atoms bonded to a central atom and the number of lone pairs of electrons on the central atom

linear

the molecular geometry about a central atom with a steric number of 2 and no lone pairs of electrons

the bond angle is 180°

trigonal planar

the molecular geometry about a central atom with a steric number of 3 and no lone pairs of electrons

the bond angles are all 120°

tetrahedral

the molecular geometry about a central atom with a steric number of 4 and no lone pairs of electrons

the bond angles are all 109.5°

trigonal bipyramidal

the molecular geometry about a central atom with a steric number of 5 and no lone pairs of electrons

three atoms occupy equatorial sites (bond angles 120°) and two other atoms occupy axial sites (bond angle 180°) above and below the equatorial plane

the bond angle between the axial and equatorial bonds is 90°

octahedral

the molecular geometry about a central atom with a steric number of 6 and no lone pairs of electrons, in which all six sites are equivalent

trigonal pyramidal

the molecular geometry about a central atom with a steric number of 4 and one lone pair of electrons

T-shaped

the molecular geometry about a central atom with a steric number of 5 and two lone pairs of electrons that occupy equatorial positions

the outer atoms occupy two axial sites and one equatorial site

square pyramidal

the molecular geometry about a central atom with a steric number of 6 and one lone pair of electrons

as typically drawn, the atoms occupy four equatorial and one axial site

square planar

the molecular geometry about a central atom with a steric number of 6 and two lone pairs of electrons that occupy axial sites

the atoms occupy four equatorial positions

bond dipole

the separation of electrical charge created when atoms with different electronegativities form a covalent bond

dipole moment (μ)

a measure of the degree to which a molecule aligns itself in a strong electric field

a quantitative expression of the polarity of a molecule

hybridization

in valence bond theory, the mixing of atomic orbitals to generate new sets of orbitals that are then available to form covalent bonds with other atoms

hybrid atomic orbital

in valence bond theory, one of a set of equivalent orbitals about an atom created when specific atomic orbitals are mixed

sp³ hybrid orbitals

a set of four hybrid orbitals with a tetrahedral orientation, formed by mixing one s and three p atomic orbitals

sp² hybrid orbitals

three hybrid orbitals in a trigonal planar orientation, formed by mixing one s and two p atomic orbitals

pi (π) bond

a covalent bond in which electron density is greatest around—not along—the bonding axis

it forms from side-on overlap of two parallel p orbitals