Valence Bond Theory

Question 1

Two Cardinal Principle of Valence Bond Theory

Answer 1

1. The greater the overlap between the atomic orbitals of adjacent atoms involved in covalent bonds, the greater the stability (lower energy) of the molecules and the stronger the covalent bond formed.
2. Covalent Bonds in molecules can best understand as extensions of the atomic orbitals which comprise the eletronic structure of atoms involved in covalent bond formation.

Question 2

What is promotion?

Answer 2

Promotion is the process of moving an electron from its lowest energy level (ground state) to some higher level atomic orbital ( an excited state). Promotion of a valence electron requires some energy since the electron is being moved from a more stable (lower energy) to a less stable (higher energy) atomic orbital.

Question 3

When does promotion occur?

Answer 3

Promotion is used whenever additional half-filled atomic orbitals are needed to form a sufficient number of covalent bonds within a molecule that would otherwise not be able to form enough covalent bonds.

Question 4

Sigma Bond

Answer 4

Results from an end to end overlap of either hybridized or unhybridized orbitals and causes a spherically-symmetrical electron density distribution around the axis of the nuclei being bonded when viewed along the axis of the two nuclei being covalently bonded.

Question 5

Pi Bond

Answer 5

caused by side to side overlap of unhybridized atomic p-orbitals in a region of space out of the plane of the nuclei being bonded. Pi bonding results in a non spherical electron density distribution around the axis of the nuclei being bonded.

Question 6

What makes up a multiple bond?`

Answer 6

One of the multiple covalent bonds will be sigma bond and the remaining bonds will be Pi bonds.

Question 7

Tetrahedral Geometries (S.N. = 4)

Answer 7

are the evidence that sp3 hybrids oribtals are present in a molecule

Question 8

Trigonal Planar Geometries (S.N. =3)

Answer 8

Trigonal Planar geometries with 120 degress bond angles are evidence that sp2 hybrid orbitals are present in a molecule (or polyatomic ion)

Question 9

Linear Geometries (S.N.= 2)

Answer 9

with bond angle of 180 are evidence that sp hybrids orbitals are present in a chemical species.

Question 10

Trigonal Bipyramidal Geometries (S.N.=5)

Answer 10

Trigonal bipyramidal geometries (S.N.=5) with bond angles of 120 degrees and 90 degress are evidence that sp3 hybrid orbitals are present in a chemical specie.

Question 11

Octahedral geometries (S.N.)

Answer 11

Octahedral Geometries with bond angles of 90 degrees are evidence that sp3d2 hybrid orbitals are present in a chemical specie.