Chapter 9 - Group 2 The Alkaline Earth Metals

state 3 physical properties of group 2

• atomic radius

• first ionisation energies

• melting points

describe the trend in atomic radius as you go down group 2

• atomic radius increases as you go down the group

• as each element has an extra filled shell

describe the trend in first ionisation energies as you go down group 2

• the first ionisation energies decrease as you go down group 2

• atomic radius increases as you go down the group

• shielding increases as you go down the group

• so weaker electrostatic force of attraction between nucleus and outermost electron

• so less energy required to remove outermost electron

why is the second ionisation energy of calcium lower than potassium

• calcium loses electron from higher energy orbital

• more shielding

what type of structure do grou 2 metals have

giant metallic

describe the trend in melting points as you go down group 2

• melting points decrease as you go down the group

• larger atomic radius as you go down the group

• so greater distance between nucleus and outermost electron

• so weaker electrostatic force of attraction that required less energy to overcome

what group 2 metal is an exception to this trend

magnesium due to its crystalline structure

group 2 metals react with:

• water

• oxygen

• dilute sulphuric acid

general equation when group 2 metals react with water

M(s) + 2H2O (l) → M(OH)2 (aq) + H2 (g)

which group 2 metal is an exception to this

magnesium

Mg equation when reacting rapidly with steam

Mg (s) + 2H2O (l) → MgO (s) + H_{2 (aq)}

state observations for this reaction

bright white light and white solid formed

Mg equation whrn reacting slowly with cold water

Mg(s) + 2H2O (l) → Mg(OH)2 (aq) + H2 (g)

what type of reaction is this

redox reaction

state the redox reaction when group 2 metal reacts with water

what is the use of magnesium hydroxide

• milk of magnesia

• antacid - neutralises the acidity of the stomach

• cures indigestion

what is the use of calcium hydroxide

• slaked lime treats acidity in soils and neutralises pH

• solution used as limewater

trends in solubility and alkalinity of hydroxides

• solubility and alkalinity increases as you go down the group

magnesium hydroxide is…

sparingly soluble

calcium hydroxide is…

slightly soluble

strontium hydroxide is…

quite soluble

barium hydroxide is…

very soluble

why does alkalinity increase as you go down the group?

• This is because solubility increases

• Metal ions get larger and charge density decreases

• So larger 2⁺ ions and lowers attractions between the OH^- ions

• The ions will split away from each other more easily

• There will be a greater concentration of OH^- ions

group 2 metals reacting with dilute sulphuric acid

 M(s) + H₂SO₄ (aq) → MSO₄ (aq) + H₂ (g)

barium sulphate uses:

• Barium meal

• Outlines gut in medical X-rays

• Test is safe as barium sulphate is insoluble

trends in solubility of sulphates

• solubility decreases as you go down the group

how to test for sulphate ions

1. add nitric or hydrochorlic acd to sample

2. ad barium chloride

3. white precipitate forms if sulphate ions present

why do we add acid to test for sulphate ions

• to remove carbonates as carbon dioxide

• barium carbonate is also the same as barium sulphate

properties of titanium

• Strong 

• Low density

what do we normally extract metals with and the general equation for this:

Most metals are found as metal oxides and extracted by carbon

General equation → MO + C → M + CO₂

why isn’t titanium extracted with carbon

Titanium can’t react with carbon as this would form TiC which is a very brittle metal

process of extracting titanium

• TiO reacts with chlorine first to form TiCl₄

• TiCl₄ is then reduced to Ti by magnesium

• TiCl₄ (l) + 2Mg (s) → 2MgCl₂ + Ti (s)

PROCESS OF FLUE GAS DESULPHURISATION

1. slurry of calcium oxide (lime) and water sprayed onto flue gas

2. flue gas reacts with calcium oxide to form calcium sulphite

3. this is further oxidised to calcium sulphate aka gypsum

uses of gypsum:

• used to make builders plaster and plasterboard

flue gas desulphurisation equation when calcium oxide used

CaO(s) + 2H2O(l) + SO2 (g) → ½ O2 (g) + CaSO4.H2O (s)

what can be used as an alternate to calcium oxide in flue gas desulphurisation

calcium carbonate (limestone)

flue gas desulphurisation equation when calcium carbonate used

CaCO3 (s) + ½ O2 (g) + SO2 (g) → CaSO4 (s) + CO2 (g)