VSEPR

Question 1

What is VSEPR theory used for?

Answer 1

VSEPR theory is used to predict and explain the shape and bond angles in various simple covalent molecules and ions.

Question 2

Repulsion of electron pairs ( Bond and Lone pair) around the central atom is in the order:

Answer 2

lp-lp > lp-bp > bp-bp.

Question 3

Why do lone pair electrons repel more than bonded pairs?

Answer 3

Lone pair electrons occupy more space around the central atom than the bond pair electrons since the lone pair is attracted by one nucleus and the bond pair is shared between two nuclei. So lone pair electrons repel more than bonded pairs

Question 4

BeCl2

Answer 4

Shape - Linear
Geometry - Linear
(Shape = Geometry)
Bond angle - 180°
B.P - 2
L.P - 0

Question 5

BF3

Answer 5

Bond pair - 3
Lone pair - 0
(Shape = Geometry)
Shape - Trigonal Planar
Geometry - Trigonal Planar
Bond angle - 120°

Question 6

CH4

Answer 6

Bond pair - 4
Lone pair - 0
(Shape = Geometry)
Shape - Tetrahedral
Geometry - Tetrahedral
Bond angle - 109.5

Question 7

Linear Geometry

Answer 7

1. Linear Geometry:
   Bonding Regions: 2 bonding pairs (no lone pairs)
   Example: BeCl₂, CO₂
   Bond Angle: 180°
   Reason: Two bond pairs are arranged opposite each other to minimize repulsion.

Question 8

Trigonal Planar Geometry

Answer 8

Bonding Regions: 3 bonding pairs (no lone pairs)
Example: BF₃, BCl₃
Bond Angle: 120°
Reason: Three bond pairs spread out equally in a plane, forming 120° angles.

Question 9

Bent or V-Shaped (Trigonal Planar)

Answer 9

Bonding Regions: 2 bonding pairs, 1 lone pair
Example: SO₂
Bond Angle: Slightly less than 120° (due to lone pair repulsion)

Question 10

Tetrahedral Geometry

Answer 10

Bonding Regions: 4 bonding pairs (no lone pairs)
Example: CH₄, SiCl₄
Bond Angle: 109.5°
Reason: Four bond pairs arrange themselves in a tetrahedral shape to minimize repulsion

Question 11

Trigonal Pyramidal (Tetrahedral)

Answer 11

Bonding Regions: 3 bonding pairs, 1 lone pair
Example: NH₃ (ammonia)
Bond Angle: Slightly less than 109.5° (~107° in NH₃)
Reason: Lone pair repels the bonding pairs more strongly, reducing the bond angle.

Question 12

Bent or V-Shaped (Tetrahedral)

Answer 12

Bonding Regions: 2 bonding pairs, 2 lone pairs
Example: H₂O (water)
Bond Angle: ~104.5°
Reason: Lone pairs exert greater repulsion, further compressing the bond angle.

Question 13

NH3

Answer 13

Bond pair - 3
Lone pair - 1
Geometry - Tetrahedral
Shape - Trigonal pyramidal
Bond angle - 107°

Question 14

Formula for Geometry and Shape of molecules?

Answer 14

Geometry = No of bond + lone pair
Shape (if lone pair present) = Geometry - lone pair

Question 15

PH3

Answer 15

Bond pair - 3
Lone pair - 1
Geometry - Tetrahedral
Shape - Trigonal Bipyramidal
Bond angle - 107

Question 16

Changes from geometry to shape are when geometry is tetrahedral?

Answer 16

1. If Geometry is Tetrahedral and one lone pair is present then shape is trigonal bipyramidal.
2. If Geometry is Tetrahedral and two lone pair is present then shape is V shaped.

Question 17

Changes from geometry to shape are when geometry is trigonal planar?

Answer 17

If geometry is Trigonal planar and one lone pair is present then its shape is v shaped.

Question 18

NH+4 (Ammonium ion)

Answer 18

Bond pair - 4
lone pair - 0
Geometry: Tetrahedral
Shape: Tetrahedral
Bond Angle: 109.5°

Question 19

NH2- (Amide ion)

Answer 19

Bond pair - 2
Lone pair - 2
Geometry - Tetrahedral
Shape - Bent
Bond angle - 104.5

Question 20

BF3 is trigonal planar but PF3 is trigonal pyramidal. Explain.

Answer 20

Despite having same number of bond pairs i.e. 3 BF3 has no lone pairs due to which it has trigonal planar shape on the other hand PF3 has one lone pair of electrons which distort the shape and give it a pyramidal shape.

Question 21

The bond angles of PF3, PCl3, PBr3 and PI3 are 97, 100, 101.5 and 102 respectively. Compare these bond angles on the basis of VSEPR theory with reason.

Answer 21

• They all have one lone pair of electrons
• Bond angle decreases with increase in electronegativity difference between the atoms
• Since fluorine is the most electronegative PF3 has the least bond angle and Iodine is the least electronegative among them PI3 has larger bond angle.

Question 22

What happens to the electron repulsion when electronegativity of central atom is higher?

Answer 22

As the electronegativity of the central atom increases, the bond pairs of electrons are pulled more towards the central atom due to which repulsion between bond pairs increases and bond angle increases.
Example:
H2O and H2S:
Electronegativity of O is greater than that of S.

Question 23

What happens to the electron repulsion when electronegativity of side atoms is higher?

Answer 23

As the electronegativity (EN) of the atoms bonded to the central atom increases, the bond pairs of electrons are pulled towards themselves by electronegative atoms due to which repulsion between bond pairs decreases. As a result, the bond angle decreases.
Example:
H2O and OF2: