Chemistry - Bonding, structure and properties

Question 1

What is ionic bonding?

Answer 1

Ionic bonding – the bonding between metal and non-metal atoms.
In all of these reactions, the metal atoms give electrons to the non-metal atoms to give both a full outer shell.

Question 2

What is covalent bonding?

Answer 2

Covalent bonding – the bonding between non-metal atoms. They share electrons

Question 3

What are the propeties of a covalent bond?

Answer 3

-strong – a lot of energy is needed to break them.

-low melting and boiling points.

-strong covalent bonds inside the molecule but weak forces of attraction between the molecules.

Question 4

How can an atom be stable?

Answer 4

Atoms are stable if their outer shell contains its maximum number of electrons.

Question 5

How do you calculate the number of covalent bonds in an atom?

Answer 5

eight minus the group number

Question 6

How are ions formed in ionic bonding?

Answer 6

-The metal atoms lose electrons to become positive ions

-non-metal atoms gain electrons to become negative ions.

Question 7

What is a giant ionic structure?

Answer 7

-Ionic compounds have giant ionic structures.
-Oppositely charged ions attract each other in a regular pattern.

Question 8

What are the properties of giant ionic structures?

Answer 8

-High melting and boiling points – due to the strength of the electrostatic forces between the ions.

-Conduct electricity when dissolved or molten – only then are the ions free to move to carry the charge.

Question 9

What are ionic lattices?

Answer 9

When oppositely charged ions in a giant ionic lattice are held together by strong ionic bonds (electrostatic forces of attraction) in a huge three-dimensional structure.

Question 10

Why do ionic lattices have high melting points?

Answer 10

It takes a lot of energy to overcome the strong electrostatic forces of attraction between oppositely charged ions, so ionic compounds have high melting and boiling points.

Question 10

What are simple covalent molecules?

Answer 10

Simple molecules contain only a few atoms held together by covalent bonds. An example is carbon dioxide (CO2), the molecules of which contain one atom of carbon bonded with two atoms of oxygen.

Question 11

What is the strength of a simple covalent molecule?

Answer 11

The covalent bonds holding the atoms together in a simple molecule are strong, the intermolecular forces between simple molecules are weak.

Question 12

What are the properties of a simple molecular substance?

Answer 12

Low melting and boiling points – this is because little energy is needed to break the weak intermolecular forces.

Do not conduct electricity – this is because they do not have any free electrons or an overall electric charge in any state of matter.

Question 13

What is a giant covalent structure?

Answer 13

-Giant covalent structures consist of lots of atoms held together by covalent bonds.

-They are arranged into giant lattices, which are extremely strong because of the large number of bonds in the structure.

Question 14

What is an allotrope?

Answer 14

A different form of the same element in the same state. For example, diamond and graphite are allotropes of carbon.

Question 14

What are the properties of giant covalent structures?

Answer 14

Very high melting points – this is because a lot of strong covalent bonds must be broken.

Variable electrical conductivity – diamond does not conduct electricity, whereas graphite contains free electrons so it does conduct electricity.

Question 15

What is graphite?

Answer 15

Graphite is a form of carbon in which the carbon atoms form covalent bonds with three other carbon atoms.

This means that each carbon atom has a ‘spare’ electron (as carbon has four outer electrons) which is delocalised between layers of carbon atoms. This can conduct electricity. These layers can slide over each other, so graphite is much softer than diamond.

Question 16

What is diamond?

Answer 16

Diamond is a form of carbon in which each carbon atom is joined to four other carbon atoms, forming a giant covalent structure. As a result, diamond is very hard and has a high melting point. It also does not conduct as it has no free electrons.

Question 17

What are nanotubes?

Answer 17

-Nanotubes are a type of fullerene and are molecular-scale tubes of carbon arranged similarly to the layers in graphite.
-Carbon nanotubes have a very high melting point, as each carbon atom is joined to three other carbon atoms by strong covalent bonds. This also leaves each carbon atom with a spare electron which means it conducts electricity.

Question 18

What are metallic bonds?

Answer 18

Metallic bonding - when metal atoms bond together
Metals form giant structures in which electrons in the outer shells of the metal atoms are free to move.
The metallic bond is the force of attraction between these free-moving (delocalised) electrons and positive metal ions.

Question 19

What are the properties of metallic bonds?

Answer 19

Metallic bonds are strong, so metals can maintain a regular structure and usually have high melting and boiling points.
Metals are good conductors of electricity and heat. This is because the delocalised electrons can move throughout the metal.

Question 20

How may the properties of metallic bonds change?

Answer 20

The greater the number of outer electrons that the metal has, the higher its melting/boiling point.
This is due to the increased positive charge on the metal ion and the increased number of electrons that are delocalised, resulting in stronger bonding.

Question 21

What is nano-silver used for?

Answer 21

-In wound dressings to prevent infection
-To coat the inside of socks and the inside of fridges to kill the bacteria that cause bad smells
-In deodorants to kill bacteria that cause bad smells
-To disinfect water supplies on the International Space Station

Question 22

What are nano-scale particles of titanium dioxide used for?

Answer 22

Can be used in sunscreen to block harmful ultraviolet light. This helps to prevent sunburn and skin cancer. These particles are so small that they cannot be seen and so make the sunscreen invisible.

Titanium dioxide nanoparticles can also be used in self-cleaning windows, as they can break down the dirt on the surface of the windows.

Question 23

What are some issues with nanoscale particles?

Answer 23

The use of nano-scale particles is relatively new, so it is not certain what the long term effect of using them will be on our health or the environment.

These particles are so small that they can easily pass through our skin and into our bloodstream. They may even be small enough to enter our cells or the cells of other organisms, and the effect that these nanoparticles could have is not known.

They can also enter the environment very easily and could cause harm to plants and animals.

Question 24

What are thermochromic pigments and what can they be used for?

Answer 24

Thermochromic pigments change colour at specific temperatures.

Examples include colour-changing novelty mugs, colour-changing spoons, battery power indicators and forehead thermometers.

Question 25

What are photochromic pigments and what are they used for?

Answer 25

Photochromic pigments change colour when exposed to light.

This can be used in clothing but is most commonly found in photochromic lenses for glasses, which darken when exposed to ultraviolet light.

Question 26

What is shape memory polymer and what is it used for?

Answer 26

Shape memory polymer is a polymer that can be bent out of its original shape and then returned to its original shape when heated.
Potential applications for this include sporting equipment, such as helmets and gum-shields or car bumpers.

Question 27

What is shape memory alloy and what is it used for?

Answer 27

Shape memory alloys are mixtures of metals that return to their original shape when heated, similar to shape memory polymers.
Again, this type of smart material could be used in sporting equipment and car bodies

Question 28

What are hydrogels and what are they used for?

Answer 28

Hydrogels can absorb up to 1,000 times their own volume in water. After this water has been absorbed, it can be released when its surroundings are dry. Changes in temperature or pH can also cause the hydrogel to release water.

Applications of hydrogels include:
hair gel
nappies
‘magic’ expanding snow
granules added to soil to help retain water for plants