C3.6 - Structure of simple molecules

Question 1

What are used in everyday life?

Answer 1

Models are used in everyday life

Question 2

Why are models used in everyday life?

Answer 2

Models are used in everyday life to help us understand things

Question 3

Models are used in everyday life to help us understanding things.
Example

Answer 3

For example, the map of the London Underground is a simplified model of the maze of tunnels carrying trains beneath the streets

Question 4

Models are used in everyday life to help us understanding things.
For example, the map of the London Underground is a simplified model of the maze of tunnels carrying trains beneath the streets.
Another example of a model used by chemists

Answer 4

An example of a model used by chemists is the diagrams of the ‘ball and stick’ model of covalently bonded structures

Question 5

What do molecular model kits use to construct molecules?

Answer 5

Molecular model kits use plastic rods to join spheres together to construct molecules

Question 6

Molecular model kits use plastic rods to join spheres together to construct molecules.
What do these models have?

Answer 6

These models have:

1. Rigid bonds
2. Solid atoms

Question 7

In giant structures, what can the models never accurately reflect?

Answer 7

In giant structures, the models can never accurately reflect the many millions of:
1. Atoms
Or,
2. Ions
bonded together in the giant lattices

Question 8

In giant structures, the models can never accurately reflect the many millions of atoms, or ions bonded together in the giant lattices.
However, what can they represent?

Answer 8

In giant structures, the models can represent a tiny fraction of the structure

Question 9

In giant structures, the models can never accurately reflect the many millions of atoms, or ions bonded together in the giant lattices.
However, in giant structures, the models can represent a tiny fraction of the structure
What can they indicate?

Answer 9

They can indicate the chemical formula of a compound by the simplest ratio of the:
1. Atoms
Or,
2. Ions
in models of their giant structures

Question 10

In giant structures, the models can never accurately reflect the many millions of atoms, or ions bonded together in the giant lattices.
However, in giant structures, the models can represent a tiny fraction of the structure.
They can indicate the chemical formula of a compound by the simplest ratio of the atoms or ions in models of their giant structures.
Example

Answer 10

For example, in a ball and stick model of sodium chloride, there will be an equal number of Na+ and Cl- ions (ratio 1:1), so its formula is NaCl

Question 11

Covalent bonds are very what?

Answer 11

Covalent bonds are very strong

Question 12

Covalent bonds are very strong.

So how are the atoms within each molecule held?

Answer 12

The atoms within each molecule are held very tightly together

Question 13

Covalent bonds are very strong.
So the atoms within each molecule are held very tightly together.
However, what does each molecule tend to be?

Answer 13

Each molecule tends to be quite separate from its neighbouring molecules

Question 14

What is the force of attraction between the individual molecules in a covalent substance?

Answer 14

The force of attraction between the individual molecules in a covalent substance is relatively small

Question 15

Why is the force of attraction between the individual molecules in a covalent substance relatively small?

Answer 15

The force of attraction between the individual molecules in a covalent substance is relatively small, because there are weak intermolecular forces between molecules

Question 16

Intermolecular forces

Answer 16

Intermolecular forces are the attraction between the individual molecules in a covalently bonded substance

Question 17

The force of attraction between the individual molecules in a covalent substance is relatively small, because there are weak intermolecular forces between molecules.
What does overcoming these forces take?

Answer 17

Overcoming these forces does not take much energy

Question 18

What is overcome, when substances made of simple molecules melt or boil?

Answer 18

When substances made of simple molecules:
1. Melt
Or,
2. Boil
,it is the weak intermolecular forces that are overcome

Question 19

When substances made of simple molecules melt, or boil, it is the weak intermolecular forces that are overcome.
What aren’t broken?

Answer 19

The covalent bonds aren’t broken

Question 20

What happens to intermolecular forces as the size of the molecules increases?

Answer 20

As the size of the molecules increases, the intermolecular forces increase

Question 21

As the size of the molecules increases, the intermolecular forces increase, so what do larger molecules have?

Answer 21

As the size of the molecules increases, the intermolecular forces increase, so larger molecules have higher:

1. Melting points
2. Boiling points

Question 22

As the size of the molecules increases, the intermolecular forces increase, so larger molecules have higher melting points and boiling points.
Example

Answer 22

For example, polymers are made from very long chain molecules, so the intermolecular forces are relatively high compared with smaller molecules

Question 23

Intermolecular forces increase with the size of the molecules, so larger molecules have higher melting points and boiling points.
For example, polymers are made from very long chain molecules, so the intermolecular forces are relatively high compared with smaller molecules.
What do these stronger intermolecular forces make polymers?

Answer 23

These stronger intermolecular forces make polymers solids at room temperature

Question 24

Polymers

Answer 24

Polymers are made up of many small reactive molecules that bond to each other to form very long chain molecules

Question 25

The simplest example of polymers

Answer 25

The simplest example of polymers is poly(ethene)

Question 26

The simplest example of polymers is poly(ethene).

What is poly(ethene) made up from?

Answer 26

Poly(ethene) is made up from thousands of small ethene molecules reacting together

Question 27

Chemical formula for ethene

Answer 27

The chemical formula for ethene is C2H4

Question 28

What will ionic compounds do when they are liquids?

Answer 28

When ionic compounds are liquids, they will conduct electricity

Question 29

Ionic compounds will conduct electricity when they are liquids.
What will a substance that is made up of simple molecules do, although it may be a liquid at room temperature?

Answer 29

Although a substance that is made up of simple molecules may be a liquid at room temperature, it will not conduct electricity

Question 30

What do compounds made of simple molecules do, even when they are molten or dissolved in water?

Answer 30

Compounds made of simple molecules do not conduct electricity, even when they are:
1. Molten
Or,
2. Dissolved in water

Question 31

Compounds made of simple molecules do not conduct electricity, even when they are molten or dissolved in water, unless they do what?

Answer 31

Compounds made of simple molecules do not conduct electricity, even when they are:
1. Molten
Or,
2. Dissolved in water
,unless they react with the water to form aqueous ions

Question 32

Compounds made of simple molecules do not conduct electricity, even when they are molten or dissolved in water, unless they react with the water to form aqueous ions, as acid molecules do.
Why is this?

Answer 32

Compounds made of simple molecules do not conduct electricity, even when they are molten or dissolved in water, unless they react with the water to form aqueous ions, as acid molecules do, because there is no overall charge on the simple molecules in a compound

Question 33

Molecular model kits use plastic rods to join spheres together to construct molecules.
These models have rigid bonds and solid atoms, but actual bonds can do what and molecules can do what?

Answer 33

These models have rigid bonds and solid atoms, but:

1. Actual bonds can vibrate
2. Molecules can bend and twist

Question 34

Compounds made of simple molecules do not conduct electricity, even when they are molten, or dissolved in water, unless they react with the water to form aqueous ions, as what do?

Answer 34

Compounds made of simple molecules do not conduct electricity, even when they are:
1. Molten
Or,
2. Dissolved in water
,unless they react with the water to form aqueous ions, as acid molecules do

Question 35

Compounds made of simple molecules do not conduct electricity, even when they are molten or dissolved in water, unless they react with the water to form aqueous ions, as acid molecules do, because there is no overall charge on the simple molecules in a compound, like what?

Answer 35

Compounds made of simple molecules do not conduct electricity, even when they are molten or dissolved in water, unless they react with the water to form aqueous ions, as acid molecules do, because there is no overall charge on the simple molecules in a compound, like sucrose

Question 36

Compounds made of simple molecules do not conduct electricity, even when they are molten or dissolved in water, unless they react with the water to form aqueous ions, as acid molecules do, because there is no overall charge on the simple molecules in a compound, like sucrose, so what?

Answer 36

Compounds made of simple molecules do not conduct electricity, even when they are molten or dissolved in water, unless they react with the water to form aqueous ions, as acid molecules do, because there is no overall charge on the simple molecules in a compound, like sucrose, so their neutral particles cannot carry electrical charge