Topic 5: Predicting Molecular Shapes with VSEPR

Question 1

Lewis Theory

Answer 1

A covalent bond is formed when 2 neighbouring atoms share an electron pair

Question 2

Octet Rule

Answer 2

Atoms share electron pairs until they have acquired an octet of valence electrons

Question 3

VSEPR Theory stands for …
It predicts …

Answer 3

Valence Shell Electron Pair Repulsion Theory
Molecular geometry + deviations, bond lengths and angles

Question 4

Regions of enhanced electron density arange themself …

Answer 4

as far as way as possible from eachother (lone pairs, bonding pairs, unpaired electrons)

Question 5

5 VSEPR Theory rules
1. Stereochemistry is determined by …
2. Relative strength of main interactions are: …
3. Geometry is determined only from …
4. Bonding pair sizes: …
5. The size of a bonding pair decreases with …

Answer 5

… valence shell electron pairs arranging themselves to minimise repulsions
… lp-lp > lp-bp > (bp-radical) > bp-bp
… the number of σ-pairs (bonding ) + lone pairs.
… A≡B > A=B > A-B
… increasing electronegativity of the ligand

Question 6

How to use VSEPR Theory:
Determine the … and how many … it has
Add total number of … donated by …
Adjust for any …
Divide by 2 = ….
Decide how to distribute the …

Answer 6

central atom (usually least electronegative) valence shell electrons
electrons
ligands
charge
number of pairs
lone + bonding pairs

Question 7

2-coordinate shape + draw (2)

Answer 7

linear (0/3 LP)
bent (1/2 LP)

Question 8

3-coordinate shape + draw (3)

Answer 8

trigonal planar (0 LP)
t-shapes (2 lone pairs at equatorial positions)
trigonal pyramidal (1 LP)

Question 9

4-coordinate shape + draw (3)

Answer 9

tetrahedral (0 LP)
square planar (2 LP)
saw horse (1 LP)

Question 10

5-coordinate shape + draw (2)

Answer 10

trigonal bipyramidal (0 LP)
square pyramidal (1 LP)

Question 11

6-coordinate shape + draw (2)

Answer 11

octahedral (0 LP)
trigonal prismatic (0 LP)

Question 12

Linear
Number of sigma-bonding & lone pairs
Hybridisation
Bond angles

Answer 12

2
sp
180

Question 13

Trigonal planar
Number of sigma-bonding & lone pairs
Hybridisation
Bond angles

Answer 13

3
sp2
120

Question 14

Tetrahedral
Number of sigma-bonding & lone pairs
Hybridisation
Bond angles

Answer 14

4
sp3
109.5

Question 15

Trigonal bipyramidal
Number of sigma-bonding & lone pairs
Hybridisation
Bond angles

Answer 15

5
sp3d
90,120

Question 16

Octahedral
Number of sigma-bonding & lone pairs
Hybridisation
Bond angles

Answer 16

6
sp3d2
90

Question 17

Pentagonal bipyramidal
Number of sigma-bonding & lone pairs
Hybridisation
Bond angles

Answer 17

7
sp3d3
72,90

Question 18

Bent
Number of sigma-bonding & lone pairs
Hybridisation
Bond angles

Answer 18

3/4
sp2/sp3
119/104.5

Question 19

T-shaped
Number of sigma-bonding & lone pairs
Hybridisation
Bond angles

Answer 19

5
sp3d
90/180

Question 20

Trigonal pyramidal
Number of sigma-bonding & lone pairs
Hybridisation
Bond angles

Answer 20

4
sp3
107

Question 21

Saw horse
Number of sigma-bonding & lone pairs
Hybridisation
Bond angles

Answer 21

5
sp3d
90/120/180

Question 22

Square pyramidal
Number of sigma-bonding & lone pairs
Hybridisation
Bond angles

Answer 22

6
sp3d2
90/180

Question 23

Octahedral
Number of sigma-bonding & lone pairs
Hybridisation
Bond angles

Answer 23

6
sp3d2
90/180

Question 24

Trigonal prismatic
Number of sigma-bonding & lone pairs
Hybridisation
Bond angles

Answer 24

6
sp3d2
60/120

Question 25

1st bond is ... 2nd and 3rd bond is ...

Answer 25

sigma pi

Question 26

Lone pair has less effect on ... bonds than ... bonds

Answer 26

pi sigma

Question 27

As the difference of electronegativity between the ligand and the central atom increases, ...

Answer 27

the electron density moves away from the central atom so the repulsion of that bond to other pairs decreases

Question 28

A radical is ... It's treated as a ... in VSEPR and the number of electron pairs will be ...

Answer 28

a species with an unpaired electron in its valence shell small lone pair n.5

Question 29

A ... is more repulsive than a radical

Answer 29

double bond

Question 30

Deviations in bond angles in CCl2F2

Answer 30

F-C-F < 109.5 < Cl-C-Cl F more electronegative so pulls pairs of electrons further way from C freeing up space and making C-F less repulsive