4. Polarity (Structure)

Question 1

why is important to know the arrangement of molecules with 3 or more atoms?

Answer 1

In order to deal with the polarity of the atoms.

Question 2

How is the geometry of the atoms understood? (2)

Answer 2

-by considering valence shell electron pair repulsion theory (VSEPR). -arranging the bonding electron pairs and lone electron pairs in the outer level of electrons so that they are positioned as far away from each other as possible.

Question 3

True or false, electron pairs will arrange themselves as far as possible from one another.

Answer 3

True. In order to avoid electron-pair repulsion.

Question 4

Why do ‘lone pairs’ repel negative charge more effectively than ‘bonding pairs’?

Answer 4

As they can be perceived to require more space around the central atom (existing in a cloud rather than linearly along the bond).

Question 5

What happens as the number of lone pairs increase?

Answer 5

The bond angle decreases.

Question 6

What needs to be determined in order to see of a molecule is polar or non-polar? (2)

Answer 6

-The electronegativity. -The structure/bonds. Note that if the bond is polar, the molecule is polar.

Question 7

What is the angle of a linear shaped molecule?

Answer 7

180^º.

Question 8

What is the angle of a linear shaped molecule, with three atoms?

Answer 8

180^º.

Question 9

What is the angle of a ‘trigonal planar’ shaped molecule?

Answer 9

120^º.

Question 10

What is the angle of a ‘tetrahedral’ shaped molecule.

Answer 10

109^º.

Question 11

What is the angle of a ‘trigonal pyramidal’ shaped molecule’?

Answer 11

107^º.

Question 12

What is the angle of an ‘angular/bent’ shaped molecule?

Answer 12

105^º.

Question 13

Which shapes contain atleast one lone pair of elections? (2)

Answer 13

• Trigonal pyramidal
• Angular/bent

Question 14

What must a molecule be if it is a polar molecule?

Answer 14

It must be a dipole.

Question 15

What are molecules called when their charge distribution is permanently uneven?

Answer 15

They are said to possess a dipole moment or are said to be polar molecules. Occuring when the molecule is asymmetrically arranged. (One has a permanent but very samll negative charge and the other end has a permanent but very small postive charge).

Question 16

True or false, if the bonds of a molecule are polar then the molecule is polar.

Answer 16

False, if the molecule has two atoms then this is true. However for molecules containing three atoms, we need to add the different dipoles in the entire structure in order to determine if the structure is polar or non-polar.

Question 17

Explain the polarity of CO₂. (2)

Answer 17

• The bonds are polar.
• The resultant dipole is zero, resulting in a symmetrical electron density being distributed, hence overall the molecule is non-polar.

Question 18

Expalin the polarity of water (H₂O).

Answer 18

• The molecule is linear and the bond dipoles do not cancel entirley. Instead they add in one direction, giving a net dipole.
• Hence the molecule is polar.