Topic 3 : Bonding and Structure

Question 1

How is an ion formed?

Answer 1

By the addition or removal of at least one electron.

Question 2

How do electron density maps provide evidence for the existence of ions?

Answer 2

Electron density maps show the likelihood of finding an electron in a particular region.
For example, the electron density map of NaCl shows that:
● Ions are arranged in a regular pattern.
● Cl- ions are larger than Na+.
● The ions are separate/discrete as the electron density between ions is zero.

Question 3

What is an ionic bond?

Answer 3

A bond between a positive and negative ion. The ions are held together by strong electrostatic attraction.

Question 4

What is an ionic crystal?

Answer 4

A giant lattice of ions, held together by the electrostatic attraction of oppositely charged ions.

Question 5

What is the trend in ionic radius down a group and why is this?

Answer 5

As you go down the group:
● Nuclear charge increases
● Shielding increases
● Electrostatic attraction decreases
Therefore atomic radius increases as there is less attraction between the nucleus and the electrons.

Question 6

How does ionic radius and ionic charge affect the strength of ionic bonding?

Answer 6

As the ionic charge increases or the ionic radius decreases, the charge density increases. This increases the strength of the ionic bond.

Question 7

What is an isoelectronic species?

Answer 7

Species with the same electronic configuration.

Question 8

What is the trend in ionic radius for a set of isoelectronic species i.e. N3- to Al3+?

Answer 8

As you go from N3- to Al3+:
● The nuclear charge increases.
● Number of electrons remains the same.
● Nuclear attraction increases.
● Ionic radius decreases.

Question 9

What is polarisation?

Answer 9

An attraction between a cation and the outer electrons of an anion can lead to the ionic bond being ‘distorted’.
If distortion is significant, it may lead to a charge cloud developing that is similar to that of a covalent bond.

Question 10

What does the polarising power of a cation depend upon?

Answer 10

It depends upon its charge density (which relies upon charge and ionic radius).
The greater the charge density, the greater the polarising power of the cation.

Question 11

What does the polarising power of an anion depend upon?

Answer 11

It depends on the ionic radius of the anion. This affects how strongly the electrons are held/attracted towards the nucleus.
The larger the anion’s ionic radius, the more
easily it is polarised.

Question 12

What is a covalent bond?

Answer 12

A bond formed that involves the sharing of electron pairs between atoms.
It forms due to the electrostatic attraction between the positive nuclei of the bonded atoms and the negative electrons which are between the two nuclei.

Question 13

What are some properties of giant covalent structures?

Answer 13

• High melting and boiling points. This is due to a network of millions of strong covalent bonds which require a lot of energy to break.
• Cannot conduct electricity. This is because there are no free charge carriers.

Question 14

What are some properties of simple molecular covalent structures?

Answer 14

• Low melting and boiling points due to the weak intermolecular forces (van der Waals between molecules).
• Cannot conduct electricity as there are no free charge carriers.

Question 15

What is a dative covalent bond?

Answer 15

A covalent bond whereby both electrons in the shared pair are donated by one of the bonding atoms only.

Question 16

Describe the structure and properties relating to graphite

Answer 16

• Each carbon atom bonded to 3 other carbon atoms.
• Layers of hexagonal rings of carbon atoms.
• Weak intermolecular forces between layers.
• One delocalised electron per carbon atom.

Question 17

Describe and explain the properties of graphite

Answer 17

• Soft/slippery because there are only weak intermolecular forces between layers which allow the layers to slide over one another.
• Electrical conductor because there is one delocalised electron per carbon atom. The delocalised electrons are mobile charges.

Question 18

Describe the structure of diamond

Answer 18

All carbon atom are covalently bonded to four other carbon atoms in a rigid, repeating structure.
No delocalised electrons.

Question 19

Describe the properties of diamond

Answer 19

• Very hard due to strong covalent bonding.
• Very high melting point due to covalent
  bonding.
• Doesn’t conduct electricity as there are no
  charged particles.

Question 20

What are the uses of graphite? Why?

Answer 20

• Electrodes - because graphite conducts electricity and has a high melting point.
• Lubricant - because it’s slippery (the layers can slide over each other).

Question 21

Why is diamond used in cutting tools?

Answer 21

Diamond is very hard

Question 22

What are the properties of graphene?

Answer 22

• High melting point due to covalent bonding between carbon atoms.
• Conducts electricity because it has delocalised electrons.

Question 23

Why is graphene useful in electronics?

Answer 23

It is extremely strong and has delocalised electrons which are free to move and carry charge.
It is only one atom thick as it is a single layer of graphite.