2.2.2 electrons, bonding and structure

Question 1

What are the three types of intermolecular forces that act between particles in all molecular substances?

Answer 1

• Induced dipole-dipole (London forces)
• permanent dipole-dipole
• hydrogen bonds

Question 2

Describe induced dipole-dipole (London) forces.

Answer 2

The weakest intermolecular force. Caused by temporary dipoles of a molecule.

Question 3

What are intermolecular forces?

Answer 3

Attractive force between molecules. Responsible for keeping matter in a solid or liquid state.

Question 4

Describe the permanent dipole-dipole interaction.

Answer 4

Weak electrostatic forces of attraction between polar molecules.

Question 5

What is a hydrogen bond?

Answer 5

The strongest intermolecular force. Acts between molecules containing polar bonds of hydrogen and fluorine/nitrogen/oxygen.

Question 6

Explain “1”

Answer 6

H₂O, HF and NH₃ all possess hydrogen bonding between molecules so have high boiling points.

Question 7

Which two factors affects the strength of induced dipole-dipole forces?

Answer 7

• More electrons = stronger force
• Close packing of molecules leads to stronger forces

Question 8

Explain “2”

Answer 8

CH4 has weak induced dipole-dipole forces between molecules.

Question 9

Explain “3”

Answer 9

Increasing boiling points due to increasing strength of induced dipole-dipole forces because of higher number of electrons in the molecule.

Question 10

What structure do ionic molecules form?

Answer 10

Giant ionic lattice

Question 11

Explain the structure of sodium chloride

Answer 11

• Oppositely charged ions are attracted to each other but repelled by their own ions.
• they form a giant ionic lattice to optimise their position, each ion is fixed

Question 12

Draw the structure of sodium chloride

Answer 12

Question 13

What happens to ionic solids when immersed in water?

Answer 13

• Ionic substances are soluble in water
• ions in structure attracted to polar water molecules and bind to them, hydrating the ions
• energy released from hydration overcomes electrostatic attraction between ions

Question 14

What are the exceptions to ionic solubility? Why?

Answer 14

Ca(OH)₂ and BaSO₄

_{hydration energy released is not enough to break ionic bonds between ions.}

Question 15

Ionic bonds- low or high melting and boiling points? Why?

Answer 15

• Giant ionic lattices have a high melting and boiling point
• a high amount of energy is needed to overcome to strong bonds between ions in the structure
• a high amount of energy is needed, therefore the melting and boiling point is very high

Question 16

Draw a diagram showing sodium chloride being dissolved

Answer 16

Question 17

In what state can ionic substances conduct electricity? Why? Why not?

Answer 17

conductivity in liquids but not solids, ions must be able to move for conductivity.

Question 18

What is metallic bonding?

Answer 18

The electrostatic attraction between positive ions and delocalised electrons of a metal.

Question 19

What factors affect the melting boiling points of metallic bonds?

Answer 19

• More delocalised electrons equals stronger bond
• smaller ionic radius holds more delocalised electrons closer to the nuclei, making stronger bond

Question 20

What structure do metallic bonds form?

Answer 20

Giant metallic lattice

Question 21

Draw a diagram showing the structure of solid sodium

Answer 21

Question 22

Draw a diagram showing the structure of solid Magnesium

Answer 22

Question 23

Why does solid magnesium have a higher melting and boiling point than solid sodium?

Answer 23

• Magnesium has a smaller atom size, more delocalised electrons and a higher ionic charge
• This gives magnesium a stronger bond than the sodium structure
• More energy is required to break Mg’s stronger bonds therefore the melting point in Mg is higher

Question 24

What are the two types of covalent structures?

Answer 24

Simple molecular lattice and giant covalent lattice

Question 25

Describe the structure of solid PCl₃

Answer 25

molecules in the solid are attracted electrostatically towards each other due to weak intermolecular forces.

Question 26

explain via diagram and word the structure of diamond

Answer 26

• Carbon atoms form 4 covalent bonds with other atoms, forming a tetrahedral shape around each atom
• strong covalent bonds between atoms need a lot of energy to be broken, therefore melting point is very high

Question 27

Explain via word and diagram the structure of graphite

Answer 27

• Flat hexagon of covalently bonded carbon atoms in sheets
• carbon sheets held together by weak intermolecular forces
• fourth outer electron of each carbon atom is delocalised, so can conduct electricity

Question 28

Describe and show the structure and properties of graphene

Answer 28

• Graphene is a single layer of graphite
• good electrical conductor due to delocalised electrons
• low mass due to singular layer

Question 29

What is a common use of graphite?

Answer 29

• Dry lubricant for machinery
• weak induced dipole-dipole bonds easily broken with little force, layers can slide over on another

Question 29

What is a common use of graphite?

Answer 29

• Dry lubricant for machinery
• weak induced dipole-dipole attraction between layers easily broken with little force so layers can slide over one-another

Question 30

What is a common use for low grade diamonds?

Answer 30

Used in industry for grinding and cutting material as it is very strong and hard

Question 31

Are giant covalent lattices soluble in water? Why/why not?

Answer 31

• Insoluble in water
• pull from polar water molecules is not strong enough to overcome the strong covalent bonds between atoms in the lattice

Question 32

Which two giant covalent lattices can conduct electricity?

Answer 32

Graphite and graphene