Chapter 6

Question 1

Electron pair repulsion theory

Answer 1

• The electrons pair surrounding the central atom determine the shape of the molecule or ion
• the electron pairs repel each other is they are arranged as far as possible
• the arrangement of electron pairs minimises repulsion and holds the bonded atoms in definite shape
• different numbers of electron pairs result in different shapes

Question 2

Why do lone pairs repel

Answer 2

• electron pairs repel as far away as possible
• lone pairs repel more strongly than bonded pairs
• lone pairs repel bonded pairs slightly closer together, decreasing the bond angle

Question 3

How much is the bond angle decreased per lone pair

Answer 3

2.5

Question 4

Shape of molecules

Answer structure

Answer 4

• The central carbon atom is bonded to 2 other atoms
• There are 2 regions of electron densities
• The two bonded regions repel each other as far as possible
• this gives the carbon dioxide molecule a linear shape
• with bond angles of 180 degrees

Question 5

Electronegativity in periodic table

Answer 5

Increases across periods
Decreases down group

Ignoring noble gases

Question 6

What are permanent dipoles

Answer 6

A difference in charge between the 2 atoms caused by a shift of electron density in the bond

Question 7

How are permanent dipoles formed

Answer 7

In a covalent bond, the bonding electrons are pulled towards the more electronegative atom

This makes the bond polar

The difference in electronegativity between the bonding atoms causes a permanent dipole

• the d+ and d- on polar molecules cause weak electrostatic forces of attraction between molecules called permanent dipoles

Question 8

Intermolecular forces

Definition

Answer 8

Forces between molecules

Weaker than covalent ionic and metallic

Question 9

What are the 3 types of intermolecular forces

Answer 9

Induced dipole-dipole (London forces)

Permanent dipole-dipole

Hydrogen bonding (strongest)

Question 10

What do induced dipole dipole forces do

Answer 10

They cause all atoms and molecules to be attracted to each other

Question 11

How are induced dipole-dipoles formed

Answer 11

• electrons in charge clouds are constantly moving
• at any given point there will always be more electrons on one side of the cloud than the other, creating a temporary dipole
• this causes another temporary dipole in the other direction of a neighbouring atom
• because the electrons are constantly moving the dipoles are created and destroyed all the time

Question 12

What factors affect induced dipole-dipole forces

Answer 12

Size
- larger molecules have larger electron clouds - stronger forces

Surface area
- they have a bigger exposed electron cloud

This causes a higher boiling point

Question 13

Intermolecular forces affect on simple covalent compounds

Answer 13

Low melting points
- weak intermolecular forces , easily overcome by heat

Polar molecules
- compounds with hydrogen molecules can form hydrogen bonds with water and dissolve

Not conductors
- don’t have an overall charge

Question 14

non polar molecules are soluble in non polar solvents

Answer 14

When a simple molecular compound is added to a non polar solvent intermolecular forces form between them

Interactions weaken the intermolecular forces breaking them so that it dissolves

Question 15

Nonpolar simple molecules are insoluble in polar solvents

Answer 15

Too strong to be overcome
No
Interactions

Question 16

Polar s8mple molecules can dissolve in polar substances

Answer 16

Attract each other

Depend on London forces

Question 17

Atoms that can form hydrogen bonds

Answer 17

Lone pair

Oxygen
Fluorine
Nitrogen