bonding theories

Question 1

what is molecular geometry?

Answer 1

general shape of a molecule, as determined by the relative positions of the atomic nuclei

Question 2

what is valence-shell electron-pair repulsion (VSEPR)?

Answer 2

model that predicts the shapes of molecules and ions that assumes the valence-shell electron pairs are arranged about each atom so that electron pairs are kept as far away from one another as possible, minimizing electron pair repulsions

Question 3

what are the steps for determining electron pair geometry?

Answer 3

1. draw the lewis structure
2. from the lewis structure, determine the steric number (SN)
3. determine optimal spatial arrangement of electron pairs to fill the molecule

Question 4

what is the equation for steric number?

Answer 4

SN= (number of atoms bonded to central atom) + (number of lone pairs on central atom)

Question 5

what are the steps for predicting molecular geometry?

Answer 5

1. write the leis structure from the formula
2. based on the lewis structure, determine the number of electron pairs around the central atoms
3. determine the arrangement of the electron pairs around the central atom
4. obtain the molecular geometry from the directions of the bonding pairs from this arrangement

Question 6

what is a polar bond? what kind of dipole moments do they have?

Answer 6

-characterized by separation of electrical charge
-nonzero dipole moment

Question 7

what is a polar molecule?

Answer 7

molecules with a dipole moment

Question 8

what is a nonpolar molecule?

Answer 8

molecules without a dipole moment

Question 9

what is valence bond theory?

Answer 9

approximate theory put forth to explain the electron pair or covalent bond by quantum mechanics

Question 10

when does a valence bond form?

Answer 10

-an orbital of one atom comes to occupy a portion of the same region of space as an orbital on the other atom
-the total number of electrons in both orbitals is no more than two

Question 11

what is promotion?

Answer 11

paired 2s electron is promoted to the unfilled orbital. Now each orbital has one electron

Question 12

what is hybridization?

Answer 12

these orbitals made in promotion are hybridized, giving four equal sp3 hybrid orbitals

Question 13

what is a hybrid orbital?

Answer 13

orbitals used to describe the bonding that is obtained by taking combinations of the atomic orbitals of the isolated atoms

Question 14

what is a sigma bond? when is one formed?

Answer 14

-cylindrical shape about the bond axis
-whether when two s orbitals overlap or with directional orbitals (p or hybrid) when they overlap along their axis

Question 15

what is a pi bond? when are they formed?

Answer 15

-has an electron distribution above and below the bond axis
-sideways overlap of two parallel p orbitals. Overlap occurs when two parallel half-filled p orbitals are available