Unit 9 Metals & Alloys [self-taught; easier]

Question 1

Compare the general physical properties of metals and non-metals, including:

Answer 1

(a) thermal conductivity

(b) electrical conductivity

(c) malleability and ductility

(d) melting points and boiling points

Question 2

properties of METALS - what & how

1. conduct heat and electricity

Answer 2

• bc metals have delocalised electrons that are able to move through the metal structure, carry a charge through the metal.

Question 3

2. malleable - (can be hammered and made into different shapes)

AND ductile - (can be drawn into wires)

Answer 3

because the layers of positive metal ions, in the metal structure, are able to slide over each other

Question 4

3. Usually have high melting and boiling points

Answer 4

because there is a strong electrostatic attraction between the positive metal ions and delocalised electrons (metallic bond)

This strong attraction / bond requires lots of energy to break

Question 5

properties of NON-METALS

1. do not conduct heat and electricity

Answer 5

bc all of the electrons are involved in covalent bonding

One exception: graphite

Question 6

2. brittle when solid

Answer 6

brittle when solid and easily break up

• not malleable or ductile (except graphite)

Question 7

3. Low melting and boiling points

Answer 7

Many non-metals are gases at room temperature bc they have weak forces between molecules

These weak intermolecular forces do not require a lot of energy to overcome

Exceptions: diamond and silicon(IV) dioxide bc of giant covalent structure and very strong covalent bonds [networks made up of a large number of non-metal atoms, held together with a very large number of covalent bonds]

Question 8

Describe the general chemical properties of metals, limited to reactions with:

(a) dilute acids - GENERAL FORMULA? what happens?

Answer 8

• 📌 metal + acid → salt + hydrogen
• the hydrogen atom in the acid is replaced by the metal atom to produce a salt

e.g. Fe

Question 9

(b) cold water and steam, producing HYDROGEN

Answer 9

• COLD WATER, 📌 metal + water → metal hydroxide + hydrogen
  e.g. Ca
• STEAM, 📌 metal + water → metal oxide + hydrogen
  e.g. Zn

Question 10

(c) oxygen

e.g.’s of what doesn’t react, what reacts easily & what reacts slowly?

general formula?

Answer 10

unreactive metals (gold, platinum) do not react with oxygen

some reactive metals (alkali metals) react easily with oxygen

copper and iron also react with oxygen, although much more slowly

📌 metal + oxygen → metal oxide

Question 11

uses of metals in terms of their
physical properties

aluminium

Answer 11

aluminium in the manufacture of aircraft because of its low density, overhead electrical cables because of its low density and good electrical conductivity, in food containers because of its resistance to corrosion

Question 12

copper

Answer 12

(d) copper in electrical wiring because of its good electrical conductivity and ductility

• pots & pans - very good conductor of heat, unreactive, malleable

Question 13

why aluminium appears to be unreactive

Answer 13

aluminium quickly reacts with oxygen to form a protective layer of aluminium oxide

Question 14

State about alloys

Why?

Answer 14

alloys can be harder and stronger than the pure metals and are more useful

bc the different sized atoms in alloys mean the layers can no longer slide over each other

Question 15

Describe an alloy

describe alloy structure

Answer 15

a mixture of a metal with
other elements

• irregular arrangement of atoms

Question 16

Examples

Answer 16

(a) brass as a mixture of copper and zinc - STRONGER, instrum. & doorknobs

(b) stainless steel as a mixture of iron and other elements such as chromium, nickel and carbon

Question 17

Uses of alloys in terms of physical properties.

Stainless steel?

Answer 17

stainless steel in cutlery because of its hardness and resistance to
rusting

Question 18

Decomposition of

1. metal hydroxide, e.g.

Answer 18

produce -> metal oxide and water

E.g. 2NaOH (s) + Δ → Na2O (s) + H2O (g)

Question 19

2. Metal carbonates decompose to produce …

e.g.

Answer 19

m car => metal oxide and carbon dioxide.

E.g., Na2CO3 (s) → Na2O (s)+ CO2 (g)

Question 20

3. metal nitrates decompose to produce…

Answer 20

metal oxide + nitrogen dioxide + carbon dioxide.

Question 21

steels & carbon in them

Answer 21

generally, steels with a higher carbon content are hard and brittle,

while steels with a lower carbon content are ductile and tough.

Question 22

steels & carbon in them

Answer 22

generally, steels with a higher carbon content are hard and brittle,

while steels with a lower carbon content are ductile and tough.

Question 23

types of steel, iron alloyed with, use, most IMPORTANT PROPERTY

Answer 23

1. MILD steel, 0.25% carbon, car body panels & wires, soft & malleable
2. high steel carbon, 0.5-1.4% carbon, tools & chisels, hard
3. low alloy steel, 1-5% of other metals (Cr, Ni, Ti), construction, bridges, high speed tools - hard & strong, low ductility & malleability
4. stainless steel, 20% chromium & 10% Ni, cutlery, sinks, chemical plants, - strong & resistant to corrosion