C7- Molecular Compounds

Question 1

What are compounds

Answer 1

Things that contain atoms of more than one atom, CHEMICALLY joined together by bonds

Question 2

Some compounds exist as molecules they have …. Structures

Answer 2

They have covalent, simple molecular structures

Eg water

Question 3

How can intermolecular forces that hold WATER or a liquid together be overcome

Answer 3

Turning the water into a gas

Question 4

Why do simple molecules mostly have low Melting and boiling points

Answer 4

It doesn’t take much energy to overcome the weak intermolecular forces

Question 5

How do you break covalent bonds

Answer 5

They have strong forces of attraction so have high melting and boiling points

Question 6

What charge do simple molecules have

Answer 6

No charge - neutral

So they can’t carry an electric current

Question 7

Why can’t covalent bonds carry an electric current

Answer 7

The strong forces between the negatively charged electrons and the positively charge nuclei hold the electrons in place so the electrons can’t flow and so carry a current

Question 8

What are monomers

Answer 8

Are small simple molecules that can be joined in a chain go form a polymer

Question 9

What’s a polymer

Answer 9

Lots of monomers joined together

Question 10

How are monomers usually linked

Answer 10

By covalent bonds between the atoms

Question 11

What do most polymers contain

Answer 11

A chain of carbon atoms

Question 12

What’s polythene

Answer 12

A common polymer made of ethane monomers

Question 13

Tell me about the length of polymer molecules

Answer 13

The longer polymers have more intermolecular forces between them

The longer chains also tend to get tangled up with one another for these reasons, longs polymers have higher melting and boiling points than shorter ones

Question 14

What are molecules

Answer 14

Groups of atoms joined by covalent bonds

Can be compounds too eg water

Question 15

What’s an allotrope and give me an example

Answer 15

Different structural forms of the same element are called allotropes

The structure and bonding in different allotropes influences their properties and uses

Carbon can form a number of different molecules

Question 16

What’s a fullerene

Answer 16

Carbon can from simple molecules called fullerenes in which each carbon atom is covalently bonded to three other carbon atoms

Fullerenes are often tubular molecules (nanotubes) or spherical.

Question 17

Tell me about fullerene melting and boiling points

Answer 17

They have weak intermolecular forces between the molecules and so have low melting points (or sublimation points) these weak forces also make them soft and slippery - however the molecules themselves are very strong due to their covalent bonding

Question 18

Tell me about graphene

Answer 18

Similar to fullerenes but it’s not a simple molecule

Consists of a sheet of carbon atoms with no fixed formula

Sheet just 1 atom thick making it the lightest known material

Covalent bonds make it extremely strong

Allows free electrons to move across its surface and so is a good electrical conductor

Question 19

Tell me about diamond and graphite

Answer 19

Two more allotropes of carbon

Both examples of covalent, giant molecular structures which have huge 3D networks of atoms linked by covalent bonds

Both have high melting points Becuase of the strong covalent bonds that need to be broken to melt the solids

Question 20

Compare diamond and graphite

Answer 20

Graphite has 3 covalent bonds for each carbon atom whereas diamond has four

This gives graphite a layered structure and means that not all of its electrons are held in covalent bonds - delocalised electrons

Question 21

What are delocalised electrons

Answer 21

Free electrons that aren’t in covalent bonds - they are free to move and carry an electrical current

Question 22

Why is graphite used for electrodes in electrolysis

Answer 22

It conducts electricity due to delocalised electrons and is cheap and not very reactive

Question 23

Why is graphite useful as a lubricant

Answer 23

The sheets of carbon atoms in graphite are held together by weak forces of attraction between layers - these weak forces allow the layers to slide past eachother which makes graphite soft and useful eg a lubricant

Question 24

Why is diamond very hard

Answer 24

Becuase it has a rigid network of carbon atoms in a tetrahedral arrangement, joined by strong covalent bonds

This property makes diamond useful for tools to cut things

It’s also an electrical insulator Becuase it had no free charged particles

Question 25

Tell me the common properties of metals

Answer 25

Solids with high melting points

Shiny (when polished)

Malleable

High density

Good conductors of electricity

Question 26

Tell me some characteristics of non metals

Answer 26

Solids, liquids, gases with low melting points

Not usually shiny when solid

Brittle when solid

Low density

Poor conductors of electricity

Question 27

How are atoms in a metallic element structured

Answer 27

The atoms are all the same size and packed closely together in layers to form a giant lattice

Question 28

Tell me about the sea of delocalised electrons in metals

Answer 28

Metal atoms have 1, 2, or 3 electrons in their outer shell - these outer shell electrons are lost from each atom and become free to move randomly throughout the metal - this leaves a giant lattice of positive metal ions surrounded by a sea of delocalised electrons which randomly move in all directions

Question 29

What’s Metallic bonding

Answer 29

Is the electrostatic attraction between the positive metal jons and the negative delocalised electrons - this attraction is so strong so metals have high melting and boiling points

Question 30

What’s malleable

Answer 30

Metals are Malleable so they can be hammered or rolled into shape without shattering

Question 31

How are metals malleable

Answer 31

When you hit a metal, the layers of ions slide over each other. The sea of electrons holds the ions together and so the metal changed shape instead of breaking

Question 32

How do metals conduct electricity

Answer 32

The delocalised electrons move randomly between the positive metal ions in all directions - when a potential difference (voltage) is applied between 2 point on a piece of metal, the electrons will flow towards the positive side

The flow of electrons transfers energy and forms an electrical current

Question 33

What’s it called when a substance can conduct electricity better

Answer 33

They have a higher electrical conductivity

Question 34

When does the electrical conductivity increase in metals

Answer 34

Is increases in metals when the number of delocalised electrons increases

Eg Na has a 1+ charge but Mg has a 2+ charge so it has a higher electrical conductivity than sodium

Question 35

Tell me the key points of ionic bonding model

Answer 35

Found in most compounds between metal and non metal atoms

The ionic bonds are formed by the loss and gain of electrons to produce oppositely charge ions that attract one another

The structure is billions of jons held together in a lattice structure

Properties: high melting and boiling points

Many are soluble in water

Conduit electricity when liquid or in solution

Question 36

Tell me the simple molecular (covalent) bonding model

Answer 36

Found in most non metal elements and compounds

The covalent bonds formed when atoms share pair of electrons

The structure is small in distinct groups of atoms

The properties are
Low melting and boiling points
A few are soluble in water
Most do not conduct electricity

Question 37

What’s the giant covalent bonding model like

Answer 37

Found in a few non metal elements and some compounds of non metals

The covalent bonds form when atoms share pairs of electrons

The structure is billions of atoms held together in a lattice structure

The properties are
High melting and boiling point
Insoluble in water
Most don’t conduct electricity (except carbon and graphite)

Question 38

Tell me the key points of the metallic bonding models

Answer 38

Found in all metals

The metallic bonds are the electrostatic attractions between the positive metal ions and negative delocalised electrons

The properties include
High melting and boiling points
Insoluble in water
Conduct electricity when solid or liquid

Question 39

Tell me the problems with the dot and cross diagram

Answer 39

Shows have electrons are shared but does not show the structure formed and they suggest that all the electrons in different atoms are different- when they are actually all the same

Question 40

Tell me the problem with the metallic model

Answer 40

Shows the metal ions held in a lattice and explains why it conducts elective but the model does not show that the jons are vibrating all the time

Question 41

Tell me the problem with the 3D ball and stick model

Answer 41

Show which atoms are joined together and show the shake of the structure - show the atoms are too far apart and there aren’t really stick holding the atoms together