Bonding, structure and properties of matter - chemistry

Question 1

What structure do ionic compounds have

Answer 1

A giant ionic lattice - the ions form a closely packed regular lattice arrangement and there are very strong electrostatic forces of attraction between oppositely charged ions, in all directions in the lattice

Question 2

Properties of ionic compounds

Answer 2

All have high melting points and high boiling points due to many strong bonds between the ions. it takes lots of energy to overcome this attraction
When they’re solid the ions are held in place so ions cannot conduct electricity, when ionic compounds kelt the ions are free to move and therefore can carry electric charge
Some ionic compounds dissolve in water. The ions separate and our free to move in the solution so they’ll carry charge.

Question 3

Issue with ball and stick model

Answer 3

• Isn’t to scale so the relative size of the ions may not be shown
• In reality there aren’t any gaps between the ions

Question 4

How to work out the empirical formula of an ionic compound from a 3d diagram

Answer 4

• Look at the diagram to work out what ions are in the compound
• Work out what charges the ion will form
• Balance the charges so the charge os the empirical formula is zero

Question 5

Covalent bonds

Answer 5

When non metal atoms share electrons with each other so that they’ve got full outer shells

Question 6

Are covalent bonds strong, why

Answer 6

The positive charge nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces, making covalent bonds very strong

Question 7

What are dot and cross diagrams useful for

Answer 7

They show which atoms the electrons in a covalent bond come from

Question 8

Issue with dot and cross diagrams

Answer 8

They don’t show the relative sizes of the atoms or how the atoms are arranged in space

Question 9

Advantage and disadvantage of displayed formula

Answer 9

• Shows how atoms are connected in large molecules
• However they don’t show the 3D structure of the molecule, or which atoms the electrons in the covalent bond have come from

Question 10

What are simple molecular substances made up of

Answer 10

Molecules containing a few atoms joined together by covalent bonds

Question 11

Properties of simple molecular substances

Answer 11

• The atoms within the molecules are held together by very strong covalent bonds by contrast the forces of attraction between these molecules are very weak
• Melting and boiling points are very low as not a lot of energy is needed to break the intermolecular forces
• Most are liquids or gases at room temp
• Molecular compounds don’t conduct electricity as they are not charged so dob’t have free electrons or ions

Question 12

What happens as molecules of simple molecular substances get bigger

Answer 12

The strength of the intermolecular forces increase so more energy is needed to break them, and the melting and boiling point increases

Question 13

How are atoms in a polymer joined

Answer 13

All the atoms in a polymer are joined by strong covalent bonds

Question 14

State of polymers at room temp and why

Answer 14

Most polymers are solid at room temperature because the intermolecular forces between polymer molecules are larger than between simple covalent molecules, so more energy is needed to break them.

Question 15

How are giant covalent structures bonded

Answer 15

All the atoms are bonded to each other by strong covalent bonds.

Question 16

Properties of giant covalent structures

Answer 16

They have very high melting and boiling points as lots of energy is needed to break the covalent bonds between the atoms
Don’t contain charged particles so they don’t conduct electricity

Question 17

Examples of giant covalent structures

Answer 17

• Diamond
• Graphite
• Silicon dioxide

Question 18

Allotropes meaning

Answer 18

Different structural forms of the same element in the same physical state

Question 19

Properties of carbon and why

Answer 19

• Made up if carbon atoms that each form four covalent bonds so diamond is really hard
• Strong covalent bonds take a lot of energy to break so diamond has a very high melting point
• No free electrons or ions so doesn’t conduct electricity

Question 20

Arrangement of graphite

Answer 20

In graphite, each carbon atom only forms three covalent bonds creating sheets of carbon atoms arranged in hexagons

Question 21

Properties of graphite

Answer 21

• There aren’t any covalent bonds between the layers - they’re only held together by weak intermolecular forces, so they’re free to move over each other. This makes graphite soft and slippery.
• Covalent bonds in the layers need loads of energy to break so graphite has a high melting point
• Only 3 out of the 4 outer electrons are used in bonds, so each carbon atom has one electron that’s delocalised, so graphite conducts electricity and thermal energy

Question 22

What is graphene

Answer 22

A sheet of carbon atoms joined together in hexagons, the sheet is just one atom thick making it a two dimensional substance

Question 23

Properties of graphene

Answer 23

• Network of covalent bonds make it very strong
• Incredibly light so can be added to composite materials to improve their strength with out adding too much weight
• Contains delocalised electrons so can conduct electricity through the whole structure.

Question 24

Molecular formula and shape of the buckminsterfullerene

Answer 24

C60 and forms a hollow sphere

Question 25

What are fullerenes

Answer 25

Molecules of carbon, shaped like closed tubes or hollow balls

Question 26

Uses of fullerenes

Answer 26

• Used to cage other molecules ie. to deliver drugs into the body
• Have a huge surface area so could help make industrial catalysts , individual catalyst molecules could be attached to the fullerene
• Lubricants

Question 27

What are nanotubes

Answer 27

Tiny carbon cylinders dress that fullerenes can form

Question 28

Properties of nanotubes

Answer 28

• Very high ratio between the length and the diameter
• Can conduct both electricity and thermal energy
• Have high tensile strength (thy don’t break when stretched)

Question 29

What is nanotechnology

Answer 29

Technology that uses very small particles such as nanotubes

Question 30

When are nanotubes used

Answer 30

Can be used in electronics or to strengthen materials without adding much weight, such as tennis racket frames

Question 31

What type of structure are metals

Answer 31

Giant structures

Question 32

How does metallic bonding work

Answer 32

The electrons in the outer shell of the metal atom are delocalised, there are strong forces of electrostatic attraction between the positive metal ions and the shared negative electrons. These forces of attraction hold the atoms together in a regular structure and are known as metallic bonding.

Question 33

Is metallic bonding strong

Answer 33

Yes metallic bonding is very strong

Question 34

Substances that are held together by metallic bonding

Answer 34

Metallic elements and alloys

Question 35

Property of metal and how that relates to its structure

Answer 35

• Solid at room temperature - The electrostatic forces between the metal atoms and the delocalised sea of electrons are very strong so need a lot of energy to be broken
• Good conductors of electricity and heat - The delocalised electrons carry electric charge and thermal heat through the whole structure
• Malleable - the layers of atoms in a metal can slide over each other so they can be bent, hammered, or rolled into flat sheets

Question 36

Difference between alloys and pure metals

Answer 36

Alloys are harder than pure metals so are more useful
Pure metals can be mixed with other metals to make them harder

Question 37

What are alloys

Answer 37

A mixture of two or more metals or a metal and another element

Question 38

How do alloys work

Answer 38

Different elements have different sized atoms so when another element is mixed with a pure metal, the new atoms will distort the layers of metal atoms, making it more difficult for them to slide over each other