Module 3 Section 1 - Structure, Bonding and Properties

Question 1

What are giant covalent lattices?

Answer 1

Giant covalent lattices are huge networks of covalently bonded atoms. Carbon atoms can form this type of structure as they can form four, strong covalent bonds.

Question 2

Examples of giant covalent lattices?

Answer 2

Diamond
Graphite
Graphene

Question 3

What are allotropes?

Answer 3

Different forms of the same element in the same state

Question 4

Structure of diamond?

Answer 4

In Diamond, each carbon atom is bonded covalently to four other carbon atoms. The atoms arrange themselves in a tetrahedral shape.

Question 5

What are the properties of diamond?

Answer 5

Because it has a lot of strong covalent bonds:

1) it has a very high melting point - it sublimes at over 3800k
2) diamond is extremely hard - used in diamond-tipped drills and saws
3) vibrations travel easily through stiff lattice, so good thermal conductor
4) it can’t conduct electricity, all outer electrons are in localised bonds
5) it won’t dissolve in any solvent

Question 6

What element is most similar to carbon?

Answer 6

Silicon. It also form a crystal lattice structure with similar properties to carbon. Each silicon atom is able to form four, strong, covalent bonds.

Question 7

What is the structure of graphite?

Answer 7

1) Carbon Atoms Are arranged in sheets of flat hexagons bonded with three bonds each.

2) the fourth outer electron of each carbon atom is delocalised between sheets of hexagons.

3) the sheets of hexagons are bonded together by weak induced dipole-dipole forces.

Question 8

What are the properties of graphite?

Answer 8

1) graphite feels slippery and is used as a dry lubricant and in pencils. This is because weak forces between graphite layers are easily broken.

2) the delocalised electrons means that electric current can flow through.

3) the layers are quite far apart so it is less dense than diamond and is used to make strong, lightweight sports equipment.

4) it has strong covalent bonds do has a very high melting point - sublime at over 3900k

5) graphite is insoluble in any solvent as the covalent bonds are too strong to break.

Question 9

What is the structure of Graphene?

Answer 9

It is a single layer of Graphene. It is one sheet of carbon atoms joined together in hexagons.

Question 10

What are the properties of Graphene ?

Answer 10

1) the delocalised electrons are free to move along the sheet, so it is a good electrical conductor.

2) the delocalised electrons also strengthen covalent bonds between carbon atoms so Graphene is extremely strong .

3) it is transparent and incredibly light.

Question 11

What are some uses of Graphene ?

Answer 11

1) high speed electronics
2) aircraft technology
3) touchscreens on smartphones / other electronic devices.

Question 12

What is the structure of metals?

Answer 12

Metals exists as giant metallic lattice structures

1) the electrons in the outermost shell of a metal atom are delocalised so electrons are free to move, leaving a positively charged metal cation eg Na+.

2) the metal cations are electrostatically attracted to the delocalised negative electrons. They form a lattice of closely packed cations in a sea of delocalised electrons.

Question 13

What are the properties of metals?

Answer 13

1) high melting point. The more delocalised electrons there are, the higher the melting point eg Mg2+ will have higher melting point than Na+.

2) metals are malleable as metal ions cab slide past each other as there are no bonds holding ions in place.

3) good thermal conductor because delocalised electrons can pass kinetic energy onto each other.

4) good electrical conductirs because delocalised electrons can carry charge.

5) metals are insoluble except in Liquid Metals, because of the strength of the metallic bonds.

Question 14

What is the structure of simple molecules?

Answer 14

They have a simple molecular structure

1) covalent bonds between atoms in the molecule are very strong. However intermolecular forces between molecules are weak and easily overcome.

2) most are diatomic or polyatomic but noble gases exist as individual atoms.

Question 15

What are the properties of simple molecular structures ?

Answer 15

1) low melting and boiling points as induced dipole - dipole forces between molecules is weak and easily overcome.

2) the more atoms in a molecule, the higher the boiling point as more London forces can form.

3) it cannot conduct electricity

4) only soluble if molecule is polarised.

Question 16

How does melting and boiling point change across a period?

Answer 16

1) for metals, melting and boiling points increase across a period because metallic bonds get stronger as the ionic radius decreases and the number of delocalised electrons increases.

2) the elements with giant covalent lattice structures (C and Si) have string covalent bonds linking all the atoms together so a lot of energy is required to break the bonds.

3) the elements that form simple molecular structures have weak intermolecular forces to overcome between their molecule so they have low melting points.

4) the noble gases have the lowest melting and boiling points in their periods as they are held together by the weakest forces.