chapter 10

Question 1

what is VSEPR? what does it predict?

Answer 1

Valence shell electron pair repulsion - predicts the 3D
geometry of a molecule
• We need the correct Lewis structure of compounds
what shape minimizes the repulsion

Question 2

what determines the shape for a compound with one central atom?

Answer 2

• For a compound with one central atom the shape is
determined by the number of electron groups around the
central atom

Question 3

what are electron groups counted as?

Answer 3

Electron groups are counted as a lone pair or a
bonding group - single/double/triple bonds all count
as 1 bonding group

Question 4

what is electron geometry?

Answer 4

the geometric arrangement of

electron groups around the central atom

Question 5

what dictates the type of electron geometry?

Answer 5

The type of electron geometry is dictated by the number

of electron groups around the central atom (2-6 groups)

Question 6

what is molecular geometry?

Answer 6

the geometric arrangement of

the bonding groups around the central atom

Question 7

what does molecular geometry describe? determined by?

Answer 7

• This geometry describes the actual 3D shape of the
molecule
• This geometry is determined by the distribution of lone
pairs and bonding groups

Question 8

what happens with two electron groups?

Answer 8

no lone pairs
linear geometry (electron &
molecular)

Question 9

what is linear geometry determined by? max repulsion?

Answer 9

!determined by repulsion between the two groups
!can get maximum repulsion at 180 degrees between
the two
!molecules with single bonds and no extra electron
groups is rare, more common are molecules with
double or triple bonds

Question 10

what happens with 3 electron groups? how can they get max separation? why do distortions occur?

Answer 10

Trigonal Planar
Can get maximum separation between the three groups
if they are 120 degrees apart
Even with no lone pairs on the central atom, distortions
can occur when the peripheral atoms contain lone pairs

Question 11

what happens with 4 electron groups? how far apart are the atoms?

Answer 11

Tetrahedral
• Harder to visualize because the 3D shape is not easily
represented in 2D
• A tetrahedral geometry has atoms 109.5 degrees apart
from each other

Question 12

what does the four electron groups look like? why isn’t it a square?

Answer 12

!Can be represented by an equilateral triangle/pyramid
(tetrahedron)
!We might assume that it would form a square planar
geometry, but then the atoms only have 90 degrees
separation from each other

Question 13

describe 5 electron groups

Answer 13

Trigonal Bipyramidal
• Three atoms are in the equatorial position and two are in
the axial position
• The axial atoms are 90 degrees apart from the equatorial
groups
• The equatorial groups are 120 degrees apart from each
other

Question 14

describe 6 electron groups (max)

Answer 14

Octahedral
• In this arrangement all 6 atoms are in equivalent
positions, no equatorial or axial positions
• All atoms are 90 degrees from each other

Question 15

what happens when an electron group is replaced by a lone pair?

Answer 15

When an electron group is replaced by a lone pair on the
central atom the typical geometries are distorted
• Lone pairs have more repulsion than electron groups

Question 16

what is electron geometry an arrangement of?

Answer 16

arrangement of electron groups

Question 17

what is molecular geometry an arrangement of?

Answer 17

arrangement of atoms

Question 18

(with lone pairs) which geometry changes? stays the same?

Answer 18

The electron geometry stays the same, but the

molecular geometry changes

Question 19

what does electron geometry influence?

Answer 19

• The electron geometry influences the molecular

geometry as we see with the bond angles

Question 20

why do lone pairs occupy more space? what are bonding electrons attracted to?

Answer 20

lone pairs occupy more space than bonding electrons
because they are attracted to only one nucleus
• Bonding electrons are simultaneously attracted to both
nuclei involved in the bond

Question 21

hierarchy (distortion of bond angles, only referring to bond angle between atoms not lone pairs )

Answer 21

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

pair-bonding pair

Question 22

what happens with 3 electron groups with 1 lone pair? ADD ANGLES (less than)

Answer 22

• Electron geometry is trigonal planar, but lone pair takes
up more space
• Resulting molecular geometry is bent, with the angle
between the two bonding groups <120º away from each
other

Question 23

max number of lone pairs for a tetrahedral electron geometry? direction of distortions? repulsion between lone pairs?
(less than 109)

Answer 23

Can have a maximum of 2 lone pairs around the central
atom
• Distortions away from tetrahedral geometry become
more pronounced as the number of lone pairs increase
• The lone pairs have more repulsion and push the
bonding groups closer together

Question 24

what happens with 1 lone pair for 5 electron groups?
ADD ANGLES (less than)

Answer 24

1 Lone pair can either occupy axial or equatorial position

• More repulsions when in the axial position

Question 25

``` what happens with 2 lone pair for 5 electron groups? ADD ANGLES (less than) ```

Answer 25

2 lone pairs also occupy the equatorial position (120 | degrees apart)

Question 26

``` what happens with 3 lone pair for 5 electron groups? ADD ANGLES (less than) ```

Answer 26

With 3 lone pairs they all occupy equatorial positions | and the molecule is linear

Question 27

``` what does 1 lone pair for a 6 electron group result in? 2? ADD ANGLES (less than) ```

Answer 27

1 lone pair results in square pyramidal shape • 2 lone pairs result in square planar with both lone pairs in the axial position

Question 28

review drawing, table in textbook

Answer 28

ok

Question 29

what does polarity depend on?

Answer 29

We know that bonds can be polar, depending on the electronegativity difference between atoms Depending on the molecular geometry the entire molecule can be polar

Question 30

what are dipole moments?

Answer 30

• Dipole moments are vector quantities and can be added | up

Question 31

4 steps to determine polarity

Answer 31

1. Draw a Lewis structure for the molecule 2. Determine the molecular geometry 3. Determine whether a molecule contains polar bonds 4. Determine whether the sum of the polar bonds cancel out

Question 32

VSPER theory summary

Answer 32

The geometry of a molecule is determined by the number of electron groups on the central atom • The number of electron groups can be determined from the Lewis structure of the molecule • Each of following count as a single electron group: a lone pair, a single bond, a double bond, a triple bond, or a single electron • Geometry of the electron groups is determined by repulsion !lone pair-lone pair> lone pair-bonding pair> bonding pair bonding pair • Bond angles vary from idealized angles because double and triple bonds (and lone pairs) occupy more space

Question 33

what is the basic principle of valence bond theory?

Answer 33

a covalent bond forms when two orbitals of two atoms overlap and a pair of electrons occupies the overlap region

Question 34

2 central themes of VB theory?

Answer 34

``` The space formed by the overlapping orbitals has a maximum capacity of two electrons that have opposite spin • The greater the orbital overlap, the stronger the bond ```

Question 35

what is the energy of a vb reaction usually like?

Answer 35

The energy of interaction is usually negative (stabilizing) when the interacting atomic orbitals contain a total of two electrons that can spin-pair • Commonly two half-filled orbitals that then spin-pair

Question 36

why is there hybridization?

Answer 36

The simplistic method cannot explain bonding in all types of molecule• Orbitals in a molecule are not the same as orbitals in an atom

Question 37

what are orbitals? (hybridization)

Answer 37

mathematical functions that describe where an electron is likely to be • If we combine these functions, we derive a new set of equations which can describe the orbitals in bonding atoms

Question 38

what are the new orbitals? what is the process of mixing them called?

Answer 38

These new orbitals are a mixture of the existing atomic orbitals • The process of mixing atomic orbitals to form new orbitals is called hybridization !Results in hybridized orbitals

Question 39

how do hybrid orbitals minimize the energy of molecules?

Answer 39

Orbitals are still localized on individual atoms, but with different shapes and energies • Hybrid orbitals minimize the energy of molecules by maximizing orbital overlap

Question 40

2 rules of hybrid orbitals

Answer 40

1. Number of standard atomic orbitals added together always equals the number of hybrid orbitals formed 2. Particular combination of standard atomic orbitals added together determine the shapes and energies of the hybrid orbitals formed

Question 41

what is the shape of sp3? what is it a hybrid of?

Answer 41

Tetrahedral shape of CH4 can be explained if we | hybridize the 2s and 2p orbitals

Question 42

are the new orbitals degenerate? describe carbons sp3

Answer 42

These new orbitals are degenerate (same energy) • Carbon’s 4 sp3 orbitals can bond with 4 H atoms • Ammonia (NH3) also has sp3 hybridized orbitals

Question 43

LOOK AT PICS FOR ORBITAL HYBRIDIZATION OF CARBON AND FORMATION OF METHANE

Answer 43

OK

Question 44

what combines to form sp2 hybridization? shape?

Answer 44

``` One s and 2 p orbitals combine to form sp2 hybridization • Orbitals have trigonal planar geometry ```

Question 45

describe sp hybridization and shape

Answer 45

``` One s and one p orbital, leaves two unhybridized p orbitals • Orbitals have linear geometry ```

Question 46

what is sp3d used for? what does it need for row 3+? | look at diagrams

Answer 46

``` Used for molecules with 5 electron groups • Need empty d-orbitals, for non-metals in row 3 and greater ```

Question 47

quantum number of arsenic unhybridized and hybridized

Answer 47

4s 4p (empty d) 4sp3d ( one in each of 5 boxes)

Question 48

when is sp3d2 used? requires?

Answer 48

``` Molecules with 6-electron groups • Also requires empty d orbitals • Use non-metals in row 3 and greater ```

Question 49

hybridization of sulfur

Answer 49

3s 3p (empty d) becomes 3sp3d2 (one in each of 6 boxes)

Question 50

look at hybridization scheme chart

Answer 50

ok

Question 51

what does vb explain

Answer 51

VB Theory explains that a covalent bond forms when two atomic orbitals overlap and two electrons with paired (opposite) spins spend more time in the overlapped regions

Question 52

how does vb theory explain molecular shape? practice hybridization questions

Answer 52

To explain molecular shape, the theory proposes that, during bonding, atomic orbitals mix to form hybrid orbitals with a different shape and direction. This process gives rise to greater orbital overlap, and thus stronger bonds • Based on the observed molecular shape, the type of hybrid orbital accounts for the shape

Question 53

what are sigma bonds? where is the highest electron density

Answer 53

Single bonds are formed from end-to-end overlap of orbitals • Sigma bonds have their highest electron density along the bond axis and is shaped liked an ellipse • All single bonds are σ bonds

Question 54

how are pi bonds formed?

Answer 54

``` The end-to-end overlap of sp2 hybridized orbitals between O and C forms a sigma bond • Side to side overlap of unhybridized orbitals forms a pi (π) bond ```

Question 55

what bond is formed from pi bonds?

Answer 55

A triple bond is formed from one sigma-bond of overlapping sp orbitals, and two pi bonds from two side-by-side unhybridized p-orbitals • Acetylene has a carbon carbon triple bond

Question 56

pi bonding in acetylene

Answer 56

``` In acetylene, both carbons are sp hybridized Unhybridized atom 2s 2p ↑↓ ↑ ↑ sp hybridized atom 2sp ↑ ↑ ↑ ↑ 2p Two unpaired electrons are in unhybridized p orbitals Lewis structure of acetylene A triple bond consists of a σ-bond between sp hybridized orbitals and two π-bonds between unhybridized p-orbitals ```

Question 57

vb theory bonding summary

Answer 57

``` End-to-end overlap of orbitals forms a sigma (σ) bond (from hybridized sp/ sp2/sp3, or unhybridized) • The side to side overlap of half-filled p-orbitals forms a pi (π) bond • A double bond always consists of a σ-bond and a πbond • A triple bond always consists of a σ-bond and two πbond ```

Question 58

5 steps to predict hybridization and bonding scheme

Answer 58

1. Start by drawing the Lewis structure 2. Use VSEPR Theory to predict the electron group geometry around each central atom 3. Select the hybridization scheme that matches the electron group geometry 4. Sketch the atomic and hybrid orbitals on the atoms in the molecule, showing overlap of the appropriate orbitals 5. Label the bonds as σ or π

Question 59

what are the limitations of vb theory?

Answer 59

• Predicts some behaviours better than Lewis Theory • There are still some properties it cannot predict !magnetic behaviour of O2 • VB theory predicts that electrons are localized inside of the orbitals ! It doesn’t account for electron delocalization

Question 60

steric number and electron geometry

Answer 60

``` Electron regions (steric number) Electronic geometry 2 linear 3 trigonal planar 4 tetrahedral 5 trigonal bipyramidal 6 octahedral ```

Question 61

how is the steric number found?

Answer 61

covalent bonds + lone pairs on electron

Question 62

bond angles

Answer 62

Electron regions (steric number) Electronic geometry Bond angles 2 linear 180∘ 3 trigonal planar 120∘ 4 tetrahedral 109.5∘ 5 trigonal bipyramidal 90∘, 120∘, and 180∘ 6 octahedral 90∘ and 180∘