4.5 Metallic bonding

Question 1

Why are metals good conductors of heat and electricity?

Answer 1

Metallic ions have a sea of delocalized electrons which allow heat and electricity to be conducted

Question 2

How are metal ions arranged?

Answer 2

Cations are arranged in a lattice structure

Question 3

Metallic bond

Answer 3

Electrostatic attraction between lattice of positive metal ions and sea of delocalized electrons

Question 4

Why is the force of attraction between metallic ions non-directional?

Answer 4

Because the force of attraction is in all directions. The electrons don’t “belong” to any atom

Question 5

Why are metals malleable and ductile?

Answer 5

If sufficient force is applied, one layer of metal can slide over another without disrupting bond

Question 6

How do metals pass electricity?

Answer 6

When voltage is applied, electrons are repelled from negative electrode and move towards positive electrode. This constitutes flow of an electric current

Question 7

How is heat passed through metals?

Answer 7

Electrons move, carrying kinetic energy from hotter parts to colder parts of the metal

Question 8

How do metals get their shininess?

Answer 8

Electrons reflect wavelengths of visible light

Question 9

What does strength of bond depend on?

Answer 9

1. Charge on metal ion

2. Ionic radius of ion

Question 10

What can be used as an approximate measure for bond strength?

Answer 10

Melting point. Stronger bond = higher M.P.

Question 11

Which has stronger metallic bond and explain why:

• K (1+, ionic radius of 138 and melting point of 63.4C)
• Ca (2+, ionic radius of 100 and melting point of 842C)

Answer 11

Calcium because:

• Higher ionic charge= more delocalized electrons which increases forces of attraction
• Smaller radius means more attraction between nuclei and electrons

Question 12

How does ionic radius affect density of metals?

Answer 12

Decrease in radius means higher charge and hence higher density

Question 13

Alloys

Answer 13

Homogenous mixtures composed of two or more metals or a metal and a non-metal

Question 14

How do properties of alloys differ from those of pure metals?

Answer 14

• More corrosion-resistant
• Stronger
• Harder

Question 15

What state do metals have to be in to make alloys?

Answer 15

Molten so that atoms can mix

Question 16

Why are alloys hard?

Answer 16

Because there is addition of different sized atoms which means they cannot slide over each other

Question 17

Are alloys more or less chemically stable than metals?

Answer 17

More chemically stable

Question 18

Composition, properties and use of brass

Answer 18

• 70% copper and 30% zinc
• Harder than copper
• Used for musical instruments

Question 19

Composition, properties and use of bronze

Answer 19

• 90% copper and 10% tin
• Harder than copper
• Used to make statues

Question 20

Composition, properties and use of stainless steel

Answer 20

• 74% iron, 18% chromium, 8% nickel
• More resistant to corrosion
• Used in cutlery

Question 21

Composition, properties and use of mild steel

Answer 21

• 99.7% iron and 0.3% carbon
• Stronger and harder than iron
• Used in construction

Question 22

Composition, properties and use of solder

Answer 22

• 50% tin and 50% lead
• Lower melting points
• Used in electric circuit boards

Question 23

Which has stronger London dispersion forces: C3H8 or C4H10?

Answer 23

C4H10 because it has higher molar mass so it has stronger forces

Question 24

Which has stronger intermolecular forces: C3H8 or C2H4O?

Answer 24

C2H4O because even though they have same molar mass, C3H8 is non-polar while C2H4O is polar hence it can form dipole-dipole forces which are stronger

Question 25

Why does Mg have 6X higher melting point than Na?

Answer 25

1. Double the delocalized electrons
2. Charge on cations is double so more attraction
3. Ionic radius is smaller so charge density is more