Bonding and structure

Question 1

What is ionic bonding ?

Answer 1

electrostatic attraction between oppositely charged ions

Question 2

Why do ionic compounds have high melting and boiling points ?

Answer 2

there is strong electrostatic attraction between oppositely charged ions, which takes lots of energy to break

Question 3

Do ionic compounds conduct electricity as a solid, and why ?

Answer 3

No, as the ions are in fixed positions and are not free to move

Question 4

Do ionic compounds conduct electricity when they are molten or aqueous ?

Answer 4

Yes, as the ions are free to move

Question 5

What is the structure of an ionic compound ?

Answer 5

giant ionic lattice

Question 6

Are ionic compounds soluble ?

Answer 6

Yes, in polar solvents

Question 7

What is metallic bonding ?

Answer 7

electrostatic attraction between positive metal ions and delocalised electrons

Question 7

Why do metallic substances have high melting and boiling points ?

Answer 7

a lot of energy is required to break the strong electrostatic attraction between the positive metal ions and delocalised electrons

Question 8

Why can metallic substances conduct electricity ?

Answer 8

metals have delocalised electrons which are free to move

Question 9

What is the structure of a metallic compound ?

Answer 9

giant metallic lattice

Question 10

What is covalent bonding ?

Answer 10

strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

Question 11

What is a dative covalent bond ?

Answer 11

a shared pair of electrons which has been donated by one of the bonding atoms only

Question 12

Why does the rule of 8 electrons in the outer shell not always work ?

Answer 12

• there may not be enough electrons (BF3)
• there may be too many electrons (SF6)

Question 13

Describe and explain the bond angle of a linear molecule.

Answer 13

• 180 degrees
• there are 2 bonding pairs and 0 lone pairs
• bonding pairs repel

Question 14

Describe and explain the bond angle of a trigonal planar molecule.

Answer 14

• 120 degrees
• 3 bonding pairs and 0 lone pairs
• bonding pairs repel

Question 15

Describe and explain the bond angle of a tetrahedral molecule.

Answer 15

• 109.5 degrees
• 4 bonding pairs and 0 lone pairs
• bonding pairs repel

Question 16

Describe and explain the structure of an octahedral molecule.

Answer 16

• 90 degrees
• 6 bonding pairs and 0 lone pairs
• bonding pairs repel

Question 17

Describe and explain the bond angle of a pyramidal molecule.

Answer 17

• 107 degrees
• 3 bonding pairs and 1 lone pair
• lone pairs repel more than bonding pairs

Question 17

Describe and explain the bond angle of a non-linear molecule.

Answer 17

• 104.5 degrees
• 2 bonding pairs and 2 lone pairs
• lone pairs repel more than bonding pairs

Question 18

How much more does a lone pair repel than a bonding pair ?

Answer 18

2.5 degrees

Question 19

What is electronegativity ?

Answer 19

the ability of an atom to attract the bonding electrons in a covalent bond

Question 20

When is a molecule non-polar ?

Answer 20

• same atoms bonded together
• hydrocarbon
• symmetrical molecule (central atom surrounded by the same atom, so dipoles cancel out)

Question 21

When is a molecule polar ?

Answer 21

• different atoms bonded together with an electronegative difference
• it has a lone pair

Question 22

How do London forces occur ?

Answer 22

• random movement of electrons causes an uneven distribution of charge
• this is an instantaneous dipole which induces a dipole in neighbouring molecules
• the dipoles in neighbouring molecules attract each other

Question 23

What are London forces ?

Answer 23

attractive forces between induced dipoles between neighbouring molecules

Question 24

What are permanent dipole-dipole forces ?

Answer 24

attractive forces between permanent dipoles of neighbouring molecules

Question 24

What affects the strength of London forces and how ?

Answer 24

- number of electrons - the more electrons, the greater the London forces

Question 24

What is needed to form a hydrogen bond ?

Answer 24

- an electronegative element (N,O or F) bonded to a hydrogen - a lone pair

Question 25

What do you need to include in a diagram of hydrogen bonding ?

Answer 25

- dipoles - the dashed line between the hydrogen and the lone pair - label of the hydrogen bond

Question 26

Why is ice less dense than water ?

Answer 26

hydrogen bonds hold the water molecules apart in an open lattice structure

Question 27

Why does water have a higher boiling point than expected ?

Answer 27

hydrogen bond are the strongest intermolecular force and so require more energy to overcome

Question 28

Which substances have giant covalent lattices ?

Answer 28

- diamond - graphite - graphene - silicon - silicon dioxide

Question 29

Why do giant covalent structures have high melting points ?

Answer 29

a lot of energy is required to break lots of strong covalent bonds between atoms

Question 30

Why are graphene and graphite good conductors of electricity ?

Answer 30

they have delocalised electrons that are free to move

Question 31

Why do other covalent substances not conduct electricity ?

Answer 31

they have no charged particles that are free to move

Question 32

Do simple molecular substances conduct electricity and why ?

Answer 32

No, as there are no charged particles that are free to move

Question 33

Are polar simple molecular compounds soluble ?

Answer 33

in polar solvents

Question 34

Are no -polar simple molecular compounds soluble ?

Answer 34

in non polar solvents