Chapter 10

Question 1

VESPR

Answer 1

valence shell electron pair repulsion theory - repulsion between electron groups on interior atoms determines the geometry of the molecule; preferred geometry is one where electron groups have max separation

Question 2

effects on bond angles

Answer 2

different types of electron groups exert slightly different repulsions; ex: double bond exerts more repulsion than single

Question 3

electron group

Answer 3

can be lone pair, single electron, single bond, double, or triple. all = 1 group

Question 4

electron group repulsions

Answer 4

lone pair - lone pair > lone pair - bonding pair > bonding pair - bonding pair

Question 5

what determines geometry of molecule

Answer 5

number of electron groups on central atom or all interior atoms

Question 6

what determines # of electron groups

Answer 6

Lewis structure - if more than 1 resonance structure, any can be used

Question 7

what determines geometry of electron groups

Answer 7

minimizing their repulsions

Question 8

why do bond angles vary from ideal?

Answer 8

double and triple bonds occupy more space than single and lone pair occupy more space than bonding groups

Question 9

symbols for drawing mol. geo. on paper

Answer 9

straight line = bond in plane of paper
hatched wedge = bond going into paper
solid wedge = hatch coming out of paper

Question 10

predicting shapes of larger molecules

Answer 10

find geometries of each atom and add together in 1 molecule

Question 11

Why can dipole moments cancel each other

Answer 11

They are vector quantities with a magnitude and direction. They can cancel if they directly oppose each other

Question 12

Process to determine if a molecule is polar

Answer 12

1. Draw Lewis structure and determine molecular geometry
2. Determine if it contains polar bonds
3. Determine if polar bonds add together to form a net dipole moment

Question 13

Why are polar molecules attracted to other polar molecules

Answer 13

They have positive and negative ends and the polar end of one is attracted to the negative end of the other

Question 14

Like dissolves like

Answer 14

Polar molecules will mix together and non polar molecules will mix together.
Polar and non polar will not mix together

Question 15

Valence bond theory

Answer 15

Electrons reside in quantum mechanical orbitals localized on individual atoms
Usually this is s p d f but could also be hybridized atomic orbitals

Question 16

When does a chemical bond form

Answer 16

When two atoms approach each other the electrons and nucleus of one interact with the other and vice versa. If energy of system is lowered from the interactions a bond forms. If it’s raised a bond will not form

Question 17

Equilibrium bond length

Answer 17

If graphed, it’s the lowest point which represents the lowest energy

Question 18

Summary of valence bond theory - 3 points

Answer 18

1. Valence electrons lie in atomic orbitals which are s p d f or hybrids
2. Chemical bonds result from the overlap of two half filled orbitals with spin pairing of the two valence electrons or the overlap of a filled orbitals with an empty one.
3. The geometry of the overlapping orbitals determines the shape of the molecule.

Question 19

how does the concept of hybridization move valence bond theory forward

Answer 19

orbitals in a molecule are not necessarily the same as the orbitals in an atom

Question 20

hybridization

Answer 20

mathematical procedure that allows us to combine standard atomic orbitals to form new atomic orbitals called hybrid orbitals that correspond more closely to actual distribution of electrons in chemically bonded atoms

Question 21

compare/contrast standard atomic orbitals and hybrid orbitals

Answer 21

both are localized on individual atoms, but have different shapes and energies

In valence bond theory a chemical bond is the overlap of two orbitals that together contain two electrons. In hybrid orbitals the electron probability density is more concentrated in a single directional lobe allowing greater overlap with orbitals of other atoms

Question 22

Why do molecules have hybrid orbitals

Answer 22

Hybrid orbitals maximize orbital overlap in a bond and minimize energy of the molecule

Question 23

Relationship between number of bonds and hybridization

Answer 23

The more bonds an atoms forms the greater the tendency to hybridize

Carbon always hybridizes because it tends to form four bonds in its compounds

Question 24

Rules for hybridization - 3 points

Answer 24

1. Number of standard atomic orbitals added together always equals number of hybrid orbitals formed. Total number of orbitals is always conserved
2. Particular combinations of standard orbitals added together will determine the shape and energy of hybrid orbitals
3. Type of hybridization that occurs is the one that yields the lowest overall energy. Use electron geometries as determined by vsepr theory to predict type of hybridization

Question 25

Sp^3 hybridization

Answer 25

Mixture of 1 s plus 3 p orbitals All hybrids orbitals have the same energy so there degenerate Tetrahedral geometry with angles if 109.5 degrees which is the same as the resulting molecule geometry Presence of a lone pair lowers the tendency of nitrogens orgitals to hybridize so 3 hybrids are involved with bonding with hydrogen atoms and the fourth contains a lone pair. This moves the bond angle to 107 degrees which is closer to the unhybridized p orbital

Question 26

Sp^2 hybrid orbital

Answer 26

Hybridization of one s and two p orbitals results in 3 sp^2 hybrids and one unhybridized p orbital 3 hybrids orbitals are in trigonal planar geometry with 120 degree bond angles and the p orbital is perpendicular to all.

Question 27

Pi vs sigma bonds

Answer 27

Pi bond is when P orbitals overlap side by side. The electron density is above and below the internuclear axis. Sigma bond is when orbitals overlap end to end Double bonds in Lewis structure always correspond to one pi and one sigma bond in valence bond theory

Question 28

Rotation around a bond

Answer 28

Rotation around a double bond is highly restricted but not restricted around a single bond isn't Restricted rotation can result in two forms with difrfor one molecule.

Question 29

Sp hybridization

Answer 29

Hybridization of one s and one p orbital results in two sp hybrids and two leftover unhybridized p orbitals Hybrid orbitals are linear with 180 degree bond angles. Unhybridized p orbitals are oriented in a plane perpendicular Triple bond consist of one sigma bond (overlapping sp orbitals) and two pi bonds (overlapping p orbitals)