2.3 - Chemical bonding, structure & properties

Question 1

Why do ionic compounds have very high melting and boiling points?

Answer 1

Because the bonds are strong and a lot of energy is needed to break them

Question 2

How can ionic compounds conduct electricity?

Answer 2

When they are heated to a molten state

• the ions can then break free of the lattice and are free to move
• the ions are charged and so can carry an electric current

Question 3

Why are ionic compounds usually soluble in water?

Answer 3

Because water molecules gave a slight electrical charge and so can attract the ions away from the lattice

Question 4

Describe metallic bonding

Answer 4

• tightly- packed layers, which forms a lattice
• outer electrons separate from the atoms and create a ‘sea of electrons’
• these electrons are delocalised and are free to move within the structure
• the metal atoms become positive ions and are attracted to the sea of electrons - metallic bonding

Question 5

Why are metals strong?

Answer 5

The layers of metal ions can slide over each other

-the metallic bonds do not break because the delocalized electrons are free to move throughout the structure

Question 6

How do metals conduct heat and electricity?

Answer 6

When a metal is heated, the delocalized electrons gain kinetic energy

• these electrons then move faster and transfer the gained energy throughout the metal
• this happens for electricity

Question 7

Why are alloys stronger?

Answer 7

Because the atoms of the added elements disrupt the regular patterns of atoms so the layers can’t slide over each other

Question 8

What are Giant Covalent structures formed from?

Answer 8

Covalent bonds

Question 9

What is an ionic lattice?

Answer 9

Where millions of ions are packed together in a lattice arrangement joined by ionic bonds

Question 10

3 properties of Giant Ionic Structures

Answer 10

• high melting and boiling points
• dissolve to form solutions that conduct electricity
• they conduct electricity when molten

Question 11

Describe Simple Molecular substances (covalent)

Answer 11

• they form very strong covalent bonds to form small molecules
• very weak forces
• low melting and boiling points
• gases or liquid at room temp
• don’t conduct electricity

Question 12

What are the uses of diamond?

Answer 12

-jewellery

-

Question 13

Describe the properties of diamond (GCS)

Answer 13

• each carbon atom contains 4 covalent bonds
• hard substance
• high melting point
• doesn’t conduct electricity

Question 14

Describe the properties of graphite (GCS)

Answer 14

• each carbon atom forms 3 covalent bonds, so sheets of carbon atoms can slide over eachother
• slippery
• high melting point
• conducts electricity

Question 15

What are the uses of graphite? (GCS)

Answer 15

• lubricant

- inside pencils

Question 16

Describe the properties of nanotubes (GCS)

Answer 16

• high tensile strength

- good heat conductor

Question 17

What are the uses of nanotubes? (GCS)

Answer 17

-used to reinforce graphite in tennis rackets

Question 18

Describe Buckminster Fullerene (GCS)

Answer 18

-sphere and will roll

Question 19

What are the uses of Buckminster Fullerene (GCS) ?

Answer 19

-catalysts

Question 20

What are smart materials?

Answer 20

Properties which change reversibly with a change in their surroundingd

Question 21

What are thermochromic pigments?

Answer 21

They change colour at a specific temperature

E.g mugs that change colour with hot liquids in them

Question 22

What are photochromic pigments?

Answer 22

They change colour with light intensity
E.g
-t-shirt design
-self darkening lenses in glasses

Question 23

What are shape memory polymers?

Answer 23

Plastics that can regain their shape when they are heated
Eg:
-sportswear such as helmets
-sealing around window frames

Question 24

What are shape-memory alloys?

Answer 24

Metal alloys that can regain their original shape when they are heated
E.g - surgical plates for joining bone fractures
-surgical wires for replacing tendons

Question 25

What are hydrogels?

Answer 25

Polymers that can absorb water and swell. Small changes in the stimulus (temp or PH) control the amount of swelling or shrinking
E.g:
-artificial muscles
-buildings threatened by forest fires
-nappies

Question 26

How do hydrogels absorb water?

Answer 26

By having strong cross links to create an open structure