2.2.2 Bonding And Structure

Question 1

What is ionic bonding?

Answer 1

The strong electrostatic attraction between positive and negative ions

Question 2

What is a giant ionic lattice?

Answer 2

A three-dimensional structure of positive and negative ions that are strongly attracted in all directions.

Question 3

What are the properties of ionic bonding?

Answer 3

• between metals and non-metals
  -electrons transferred from metal to non-metal
• metal forms +ve ion and non-metal forms -ve ion
• oppositely charged ions have strong electrostatic attraction

Question 4

What is the structure of ionic compounds?

Answer 4

Giant ionic lattice
3D structure of oppositely charged ions. Ions attract each other in all directions

Question 5

What are the mpt and bpt of ionic compounds?

Answer 5

High mpt + bpt
Strong electrostatic attraction between +ve and -ve ions - requires a large amount of energy to overcome and break bonds
More highly charged ions = greater electrostatic attraction between ions

Question 6

What is the conductivity of ionic compounds?

Answer 6

Don’t conduct electricity in solid state - fixed position in lattice
When molten or dissolved ions are free to move and current can flow

Question 7

What is the solubility of ionic compounds?

Answer 7

Many compounds soluble in water
As dissolves, lattice breaks down and ions are released into solution and ions are stabilised by coordination to water molecules.
Ionic compounds are soluble in polar substances

Question 8

What is a covalent bond?

Answer 8

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

Question 9

Why do atoms expand their octet?

Answer 9

Usually atoms can form enough covalent bonds to obtain noble gas configuration- not always possible
- elements in period 3 or above can expand their octet using d-orbitals
- they do this as unpaired electrons pair up and the no that can pair up is equivalent to no of electrons in outer shell

Question 10

What is a dative bond?

Answer 10

A covalent bond where the shared pair of electrons is provided by one of the bond atoms only.

Question 11

When does covalent bonding take place?

Answer 11

Between non-metals
Electrons are shared between atoms
Can form simple molecular
Or giant structures e.g. diamond

Question 12

What is average bond enthalpy?

Answer 12

Measurement of covalent bond strength

Question 13

What is electron pair repulsion theory?

Answer 13

• the shape of a molecule is determined by the number of electron pairs in the outer shell of the central atom
  # the electron pairs repel each other and arrange themselves as far apart as possible

Question 14

What is a linear shape?

Answer 14

2 bp
180° bond angle

Question 15

What is a trigonal planar shape?

Answer 15

3bp
120° bond angle

Question 16

What is a tetrahedral shape?

Answer 16

4 bp
109.5° bond angle

Question 17

What is a trigonal bipyramid shape?

Answer 17

5bp
90 and 120° bond angle
(see notes)

Question 18

What is an octahedral shape?

Answer 18

6bp
90° bond angle

Question 19

What happens when molecules have lone pairs?

Answer 19

Lone pairs repel more than bond pairs
Lp-lp > lp-bp > bp-bp
Each lone pair reduces the bond angle by 2.5

Question 20

What is a non-linear shape?

Answer 20

2bp 2lp
Tetrahedral without 2 bonds
104.5° bond angle

Question 21

What is a pyramidal shape?

Answer 21

3bp 1lp
Tetrahedral without 1 bond
107° bond angle

Question 22

M3 to cm3

Answer 22

X 1,000,000

Question 23

Describe simple molecular covalent

Answer 23

Atoms in molecule held together by strong covalent bonds
The molecules are held together with weak intermolecular forces
These could be:
London forces
Permanent dipole-dipole
Hydrogen bonds

Question 24

Why are melting points of simple molecular substances low?

Answer 24

Not a large amount of energy needed to break the weak intermolecular forces. Covalent bonds aren’t broken bc they are strong

Question 25

What is the electrical conductivity of covalent compounds?

Answer 25

Don’t conduct electricity because there are no free electrons or charged particles to move.

Question 26

What is the solubility of covalent simple molecular structures?

Answer 26

Dissolve in organic (non-polar) solvents But not in polar solvents such as water Bc bonds need to be broken in the molecular structure and new bonds formed with solvent molecules (weak London forces are able to form between covalent molecules and these solvents, helping…)

Question 27

Describe the structure of graphite

Answer 27

Each C is bonded to 3 other C atoms by STRONG COVALENT bonds. Each C atom has one further electron that contributes to the sea of delocalised electrons between LAYERS OF HEXAGONAL RINGS. Electron between layers = attractive force (albeit weak) that holds the layers together.

Question 28

Describe the structure of diamond

Answer 28

Each C atom is bonded to 4 other C atoms with strong covalent bonds in a tetrahedral shape around each C.

Question 29

What is the mpt and bpt of giant covalent structures?

Answer 29

Very high Covalent bonds need to be broken and this takes up a large amount of energy

Question 30

What is the electrical conductivity of giant covalent structures?

Answer 30

Diamond doesn’t conduct electricity - no free electrons, they are used in covalent bonds Graphite can conduct electricity - electrons between layers are able to move parallel to layers when voltage is applied

Question 31

What is the solubility of giant covalent structures?

Answer 31

To dissolve them would need huge amounts of energy as covalent bonds would need to be broken

Question 32

What is metallic bonding?

Answer 32

Atoms in solid metal are held together by metallic bonding Atoms are ionised +ve ions (cations) occupy fixed positions in the lattice outer shell electrons are delocalised and shared between all atoms in metallic structure Metal is held together by attractions between all positive ions and negative electrons (especially delocalised electrons)

Question 33

Describe metallic bonding structure

Answer 33

Delocalised electrons spread throughout the structure Electrons can move within the structure Charges are balanced over whole structure Lattice of positive ions in fixed positions surrounded by sea of delocalised electrons that can move

Question 34

What are the mpt and bpt of metals?

Answer 34

High Electrons free to move through structure but ions fixed Strong attraction between +ve ions and -ve electrons High temperature needed to overcome metallic bonds and dislodge from rigid positions in lattice

Question 35

What is the conductivity of metals?

Answer 35

Delocalised electrons can move freely and so metals can conduct electricity even when solid

Question 36

What is the malleability and ductility of metals?

Answer 36

Ductile - can be drawn out and stretched, can be drawn into wires Malleable - can be hammered to different shapes Due to movement of delocalised electrons, atoms or layers can slide past each other