Structure and Bonding

Question 1

What are giant covalent structures also known as?

Answer 1

Macromolecules

Question 2

Covalent bonding vs ionic bonding - metals or non metals?

Answer 2

Ionic = metal + non metal
Covalent = non metals

Question 3

In terms of electrostatic attraction, how do two atoms bond together in a covalent bond?

Answer 3

The shared electrons create an electrostatic attraction between the positively charged nuclei and the negatively charged shared electrons. This attraction pulls the two atoms together, holding them in the bond.

Question 4

Compare dot and cross diagram with 2d ball and stick model and 3d ball and stick model.

Answer 4

2d ball and stick model shows which atoms are bonded but not the molecule’s true shape. 3d models can do this. Dot and cross diagrams show which atom the electrons in the bonds came from originally and cant represent the whole structure.

Question 5

What’s the difference between the covalent bond and the intermolecular forces between it’s molecules?

Answer 5

The intermolecular forces are between the molecules- so to other atoms not involved in the covalent bond that forms the molecule. The covalent bond is very strong but the intermolecular force is weak.

Question 6

What happens to intermolecular forces as the molecules become bigger?

Answer 6

The size of the force increases, so larger molecules have higher melting and boiling points. Molecules with strong intermolecular forces and larges sizes can be polymers.

Question 7

What is a polymer?

Answer 7

A series of molecules that bond to each other to form long chains.

Question 8

Why do compounds of simple molecules not conduct electricity?

Answer 8

Because there is no overall charge to their molecules so they cannot carry electrical charge like an ion. The only way a simple molecule can conduct electricity is to react with water to form aqueous ions.

Question 9

What are giant covalent structures?

Answer 9

Huge networks of atoms held together by strong covalent bonds in giant covalent structures. Examples are diamond, graphite, graphene and silicon dioxide.

Question 10

Properties of giant covalent structures?

Answer 10

Very high melting and boiling points, insoluable in water, besides graphite they are hard and do not conduct electricity

Question 11

Describe the structure of graphite

Answer 11

In graphite, carbon atoms are only bonded to three other carbon atoms, forming hexagons in layers. There are no covalent bonds between layers, only intermolecular forces so the layers can slide, making graphite soft.

Question 12

What is special about graphite’s electrons?

Answer 12

Their electrons are delocalised and can move freely between layers. They allow graphite to conduct electricity. Graphite is also a good thermal conductor. This is as more heat is supplied, the faster they can move between layers.

Question 13

Describe the shape of a fullerene

Answer 13

A fullerene is a type of molecule made entirely of carbon atoms arranged in a series of hexagons and pentagons, (and seven sided shapes) forming a hollow structure.

Question 14

What are cylindrical fullerenes?

Answer 14

Carbon nanotubes that form thin cylinders. They have high tensile strength so can be used to reinforce things like tennis rackets. They have high electrical conductivity due to their delocalised electrons. Fullerines in general are also used as cages to deliver medicines into the body like radioactive tracers and cancer therapies. It is also used as a lubricant.

Question 15

What is graphene?

Answer 15

A sheet of graphite - hexagonal interlocking carbon atoms in just one layer. It is an even better conductor of electricity and thermal energy as has low density, high reactivity and is very strong for its mass.

Question 16

Why does Diamond have a high melting point?

Answer 16

Because arranged in rigid crystal structure where carbon atom is covalently bonded to four other bonds.

Question 17

Why is HCl’s melting point lower than NaCl?

Answer 17

HCL is a simple molecule held by weak intermolecular forces which are easy to overcome with a low temperature. NaCl is made of ions with strong ionic bonds which are harder to break.

Question 18

What is an allotrope? Give examples for carbon.

Answer 18

An allotrope is different forms of the same element is the same state. They have different chemical and physical properties. Carbon allotropes = diamond, graphite and graphene.

Question 19

What are the properties of a giant covalent structure?

Answer 19

• high melting and boiling point, - hard - non conductive - brittle - insoluble

Question 20

What is the first fullerine?

Answer 20

Buckministerfullerine C60.

Question 21

Why do the atoms of metals form crystals?

Answer 21

Because the atoms are built up layer on layer in a regular pattern and often form giant structures.

Question 22

Why can metals/ metallically bonded elements conduct?

Answer 22

because the outer electron from each atom can move throughout the giant structure as a delocalised electron, surrounding the positively charged metal ions. Strong electrostatic attraction between negative electrons and positive ions bond the metal ions together.

Question 23

Why can metals be bent/shaped without breaking?

Answer 23

Because the layers of atoms are arranged regularly, so they can slide over each other.

Question 24

What is an alloy?

Answer 24

An alloy is a mixture of two or more elements, at least one of which is a metal.

Question 25

Why are alloys harder than pure metals?

Answer 25

Alloys, containing a mixture of two or more elements with one or more being a metal, contains atoms of different sizes. This makes it difficult for the layers to slide over each other.

Question 26

Why do metals conduct electricity and thermal energy?

Answer 26

(This means they they have high boiling and melting points too.) The electrostatic attraction between a metal’s delocalised electron and its positive ion holds the metal in place, but also allows the metal to conduct as the electrons can move and carry charge. The fact metals exist in giant structures also means the electrostatic forces of attraction are in all directions. It therefore takes a lot of energy to separate the metal ions and break the structure.

Question 27

Why are metals malleable?

Answer 27

When the delocalised electrons move when heated, it can distort the layers making the metal malleable.

Question 28

How big is a nanometre compared to microparticles?

Answer 28

1 x 10^9 metres (a nanometre) versus 1 x 10^6 metres ( a micrometre).

Question 29

What objects are typically measured in micrometres? What are PMs?

Answer 29

The particles in air like pollen and dust. These are known as particulate matter (PM).

Question 30

Why are nanoparticles highly reactive?

Answer 30

Because they have a large amount of their atoms exposed at the surface of the particle (they have a large surface area to volume ratio).

Question 31

Why are nanoparticles useful?

Answer 31

Their size means smaller amounts of materials like catalysts are needed for industrial and manufacturing purposes.

Question 32

Give 2 examples of the uses of nanoparticles.

Answer 32

Glass can be coated in titanium oxide nanoparticles. When sun lands on the window it reacts to break down dirt, which rain can wash away.
Titanium and zinc oxide are used in sunscreen and covered in silica to better block sunrays.

Question 33

Why are scientists worried about nanoparticle risks for causing an explosion or damaging the environment?

Answer 33

Their large surface area to volume ratio makes them extremely reactive and can ignite a spark. Nanoparticles are small and can seep into waterways, eg if used in washing detergent. There is also a concern of nanoparticles entering the bloodstream or lungs from being absorbed from cosmetics and medicines.