EL - Giant covalent and metallic structures

Question 1

Apart from small molecules, what can covalent bonding lead to?

Answer 1

Huge, great lattices containing billions and billions of atoms.

Question 2

What do giant covalent lattices have?

Answer 2

A huge network of covalently bonded atoms.

Question 3

What are the electrostatic attractions like in giant covalent structures compared to those in simple covalent molecules?

Answer 3

The electrostatic attractions holding the atoms together in these structures are much stronger than the electrostatic attractions between simple covalent molecules.

Question 4

What are examples of elements that can form these giant, covalent structures?

Answer 4

Carbon and silicon.

Question 5

Why can carbon and silicon form giant, covalent structures?

Answer 5

Because they can each form 4 strong, covalent bonds.

Question 6

What arrangement do silicon and carbon form bonds in?

Answer 6

A tetrahedral arrangement.

Question 7

What provides evidence for covalent bonding?

Answer 7

The properties of giant structures.

Question 8

What can the properties of giant structures provide evidence for?

Answer 8

Covalent bonding.

Question 9

What helps determine a substance’s properties?

Answer 9

The forces holding individual particles together.

Question 10

What are the 5 common properties of giant covalent structures?

Answer 10

Very high melting points.
Often extremely hard.
Are good thermal conductors.
Insoluble in polar solvents.
Can't conduct electricity.

Question 11

Why do giant covalent structures have very high melting points?

Answer 11

You need to break a lot of very strong bonds before the substance melts, which takes a lot of energy.

Question 12

Why are giant covalent structures very hard?

Answer 12

Because of the very strong bonds all through the lattice arrangement.

Question 13

Why are giant covalent structures good thermal conductors?

Answer 13

Since vibrations travel easily through the stiff lattices.

Question 14

Why won’t giant covalent structures dissolve/ why are giant covalent structures insoluble?

Answer 14

The covalent bonds mean atoms are more attracted to their neighbors in the lattice than to solvent molecules. The fact that they are all insoluble in polar solvents like water shows us that they don’t contain ions.

Question 15

What does the fact that all giant covalent structures are insoluble in polar solvents show us?

Answer 15

Shows us that they don’t contain ions.

Question 16

Why can’t giant covalent structures conduct electricity?

Answer 16

Since there are (in most giant lattice structures) no charged ions or free electrons (all the bonding electrons are held in localised electron bonds).

Question 17

What example of a giant covalent structure is an exception to the “can’t conduct electricity rule” and why?

Answer 17

Graphite - a form of carbon.

Carbon atoms form sheets, with each carbon atom sharing three of its outer shell electrons with other carbon atoms. This leaves the fourth outer electron in each atom fairly free to move between the sheets, making graphite a conductor.

Question 18

How are the individual sheets in graphite held together?

Answer 18

By relatively weak forces.

Question 19

What do metal elements exist as?

Answer 19

Giant metallic lattice structures.

Question 20

Explain the structure of a giant metallic lattice:

Answer 20

Electrons in the outermost shell of the metal atoms are delocalised - they are free to move. This leaves a positive metal ion.

The positive metal ions are attracted to the delocalised negative electrons. They form a lattice of closely packed positive ions in a sea of delocalised electrons - this is metallic bonding.

Question 21

What explains why metals do what they do?

Answer 21

The metallic bonding model.

Question 22

What are the 5 common properties of metals?

Answer 22

High melting points.
Can be shaped and are ductile.
Good thermal conductors.
Good electrical conductors.
Insoluble, except in liquid metals.

Question 23

Why do metals have high melting points?

Answer 23

Because of the strong metallic bonding.

Question 24

What affects the melting point of metals?

Answer 24

The number of delocalised electrons per atom. The more electrons there are, the stronger the bonding will be and the higher the melting point.

Also, the lattice structure and the size of the metal ion affect the melting point.

Question 25

Why can metals be shaped/why are they ductile?

Answer 25

As there are no bonds holding specific ions together, the metal ions can slide over each other when the structure is pulled.

Question 26

Why are metals good thermal conductors?

Answer 26

The delocalised electrons can pass kinetic energy to each other.

Question 27

Why are metals good electrical conductors?

Answer 27

Because the delocalised electrons are free to move and can carry a current.

Question 28

What can reduce the electrical conductivity of a metal and how?

Answer 28

Any impurities can dramatically reduce electrical conductivity by reducing the number of electrons that are free to move and carry charge - the electrons transfer to the impurities and form anions.

Question 29

Why are metals insoluble, except in liquid metals?

Answer 29

Because of the strength of the metallic bonds.