How structure influences properties/uses of substances

Question 1

Substances that are simple molecules normally have what state at room temperature?

Answer 1

Gas or liquid, because of their low melting and boiling points.

Question 2

Why are most simple molecules gas or liquid at room temperature?

Answer 2

There are weak intermolecular forces acting between the simple molecules which can be overcome with small amounts of energy thus giving them low melting and boiling points. It is not the covalent bonds that are overcome, just the intermolecular forces.

Question 3

Substances that consist of simple molecules do not conduct electricity. Why?

Answer 3

The molecules do not have an overall charge and for a substance to conduct electricity there must be charge and movement.

Question 4

Ionic compounds have what structure?

Answer 4

Regular structures (giant lattices).

Question 5

Giant ionic lattices are caused by what?

Answer 5

Strong electrostatic attractions between oppositely charged ions.

Question 6

Ionic compounds have what properties?

Answer 6

High melting and boiling points due to large amounts of energy being required to break the electrostatic bonds.

Question 7

Ionic compounds can conduct electricity when and why?

Answer 7

When melted or dissolved in water because the ions have charge and are free to move.

Question 8

Atoms that bond covalently can form what kinds of structures?

Answer 8

Giant covalent structures.

Question 9

Examples of giant covalent structures:

Answer 9

Diamond (carbon).
Graphite (carbon).
Silicon dioxide (silica).

Question 10

Properties of giant covalent structures:

Answer 10

High melting and boiling points.

Question 11

In diamond each carbon atom has how many bonds?

Answer 11

4 covalent bonds.

Question 12

In graphite each carbon atom has how many bonds?

Answer 12

3 covalent bonds.

Question 13

What properties does graphite have due to the number of bonds for each carbon atom?

Answer 13

It is very soft because there are no bonds between the layers of atoms meaning they can easily slide over one another.
It can conduct heat and electricity well due to one delocalised electron per atom.

Question 14

What giant covalent structure can carbon form other than graphite and diamond?

Answer 14

Fullerenes.

Question 15

Fullerenes can be used for what?

Answer 15

Drug delivery in the body.
Lubricants.
Catalysts.
In nanotubes for reinforcing materials.

Question 16

Delocalised electrons give metals what properties?

Answer 16

Good conductors of heat and electricity.

Question 17

Metals are malleable and ductile. Why?

Answer 17

There are layers of atoms inside the metal that can easily slide over one another.

Question 18

Differences between alloys and metals:

Answer 18

Alloys are usually made as a mixture of two or more different metals.
The different sized atoms of alloys distorts the layered structure meaning alloys are harder than pure metals.

Question 19

Shape memory alloys do what?

Answer 19

Return to their original shape after being deformed. An example is Nitinol in dental braces.

Question 20

Differences between low density (LD) and high density (HD) polymers.

Answer 20

Properties of each depend upon the conditions in which they were formed. LD and HD polymers are produced using different catalysts and reaction conditions.

Question 21

Thermosoftening polymers are…

Answer 21

…polymers that can be reheated and remoulded into a shape.

Question 22

Molecular structure of a thermosoftening polymer?

Answer 22

Layers of molecules but weak intermolecular bonds.

Question 23

Thermosetting polymers are…

Answer 23

…polymers that are set into a shape and cannot be remoulded if reheated. Their shape is permanent.

Question 24

Molecular structure of a thermosetting polymer?

Answer 24

Layers of molecules with cross links (bonds) between them.

Question 25

Nanoscience refers to structures that are…

Answer 25

…1-100 nm in size.

Question 26

Nano particles have a high what compared to the same materials in bulk?

Answer 26

Surface area to volume ratio.

Question 27

Uses of nanoscience:

Answer 27

Development of new computers.
Development of new catalysts.
Development of new coatings.
Development of highly selective sensors.
Development of stronger and lighter materials.
Development of cosmetics (suncream and deodorants).