Chapter 6 Shapes of molecules and intermolecular forces

Question 1

What is the electron-pair repulsion theory?

Answer 1

• Electrons have negative charges and repel each other
• The electron pairs surrounding a central atom determine the shape of that molecule
• The electron pairs repel one another so that they are arranged as far apart as possible
• This arrangement minimises repulsion and holds the molecule in a definite shape

Question 2

Why do lone pairs repel stronger than bonded pairs?

Answer 2

Lone pairs are slightly closer to the central atom

Question 3

What shape has 4 bonding pairs and 0 lone pairs?

Answer 3

Tetrahedral

Question 4

What shape has 3 bonding pairs and 1 lone pair?

Answer 4

Pyramidal

Question 5

What shape has 2 bonding pairs and 2 lone pairs

Answer 5

Non-linear

Question 6

What shape has 2 bonding pairs and 0 lone pairs?

Answer 6

Linear

Question 7

What shape has 3 bonding pairs and 0 lone pairs?

Answer 7

Trigonal planar

Question 8

What shape has 6 bonding pairs and 0 lone pairs

Answer 8

Octahedral

Question 9

What is electronegativity?

Answer 9

The attraction of a bonded atom for the pair of electrons in a covalent bond

Question 10

What electronegativity difference is considered to be a covalent bond

Answer 10

0 difference

Question 11

What electronegativity difference is considered to be polar covalent

Answer 11

0 to 1.8

Question 12

What electronegativity difference is considered to be an ionic bond?

Answer 12

greater than 1.8

Question 13

When is a bond non-polar?

Answer 13

When the bonded atoms are the same or have similar electronegativity values

Question 14

When is a bond polar?

Answer 14

When the bonded atoms have different electronegativity values

Question 15

What is a dipole?

Answer 15

A separation of opposite charges

Question 16

What are intermolecular forces?

Answer 16

Weak interactions between dipoles of different molecules

Question 17

What are the three main categories of intermolecular forces?

Answer 17

• Induced dipole-dipole interactions (London forces)
• Permanent dipole-dipole interactions
• Hydrogen bonding

Question 18

What are London forces?

Answer 18

Weak intermolecular forces that exist between all molecules, whether polar or non-polar.

Question 19

How does induced dipoles occur?

Answer 19

• Movement of electrons produces a changing dipole in a molecule
• At any instant, an instantaneous dipole will exist
• That instantaneous dipole induces a dipole on a neighbouring molecule
• Which goes on to further induce dipoles on neighbouring molecules

Question 20

What is a simple molecular lattice?

Answer 20

A lattice with molecules that are held in place by weak intermolecular forces

The atoms within each molecule are bonded together strongly by covalent bonds

Question 21

What is the electrical conductivity of simple molecular substances?

Answer 21

There are no mobile charged particles in simple molecular structures, with no charged particles that can move, there is nothing to complete an electrical circuit therefore simple molecular substances cannot conduct electricity

Question 22

What is the solubility of simple molecular substances?

Answer 22

-Non polar substances tend to be soluble in non-polar solvents

Question 23

Why are non-polar simple molecular substances soluble in non-polar solvents?

Answer 23

• When a simple molecular compound is added to a non-polar solvent, intermolecular forces form between the molecules and the solvents
• The interactions weaken the intermolecular forces in the simple molecular lattice which cause the intermolecular forces to break and the compound dissolves

Question 24

Where are hydrogen bonds found

Answer 24

Between Oxygen, Nitrogen or Fluorine

Question 25

What are the two anomalous properties of water resulting from hydrogen bonds?

Answer 25

Ice is less dense than liquid

Water has a relatively high melting and boiling point

Question 26

Why is ice less dense than liquid?

Answer 26

• Hydrogen bonds hold water molecules apart in an open lattice structure
• The water molecules in ice are further apart than in water
• Solid ice is less dense than liquid water and therefore floats

Question 27

Why does water have a relatively high melting and boiling point?

Answer 27

• Hydrogen bonds are extra forces over the london forces
• More energy is required to break the hydrogen bonds in water
• Therefore, water has a higher boiling and melting point