A-level Chemistry: 3.2.2 Group 2, The Alkaline Earth Metals

2

(all end s2 & make 2+ ions)

Increases

• Number of shells increase
  

  • More distance between nucleus and outer electrons

• Outer shells more shielded

• Less attraction between nucleus and outer electrons

Decreases

• Number of shells increase
  

  • Increased distance between nucleus and outer electrons

• Outer shells more shielded

• Less attraction between nucleus and outer electrons

• Easier to remove outer electron = less energy

Increases

1. First ionisation energy decreases down group
   

   • Due to increasing atomic radius and shielding effect

2. When Group 2 elements react = lose electrons & form positive ions
   

   • Easier it is to lose electrons (i.e. the lower the 1st and 2nd ionisation energies) = more reactive the element

   • So reactivity increases down group

Generally Decrease

Metallic structures

• Positive ions in crystal structure surround by delocalised electrons from outer electron shells

• Size of positive ion increases, but charge remains the same

• Delocalised electrons further away from positive ions

• Weaker electrostatic forces of attraction between positive ions and delocalised electrons

• Weaker metallic bonds = less energy needed to break

∵ crystal structure (arrangement of metallic ions) changes

Water

When they react with water, they are oxidised from start of 0 to +2 forming M2+ ions

Metal hydroxide and hydrogen

M(s) + 2H₂O(l) → M(OH)₂(aq) + H₂(g)
(where M = Group 2 metal)

more readily

∵ ionisation energies decrease

Compound Anion

1. Generally, compounds of Group 2 elements that contain singly charged negative ions (e.g. OH-) ↑ in solubility down group

2. Compounds that contain doubly charged negative ions (e.g. SO4-2) ↓ in solubility down group

• Magnesium → least soluble | most soluble

• Calcium → ↓ solubility | ↑ solubility

• Strontium → ↓ solubility | ↑ solubility

• Barium → most soluble | least soluble

Sparingly soluble

insoluble

1. Add dilute hydrochloric acid and then barium chloride solution, BaCl2(aq)

2. If white precipitate of barium sulfate forms = original compound contained sulfate

To get rid of any lurking sulfites or carbonates which will also produce a white precipitate

To neutralise acidity

• Calcium hydroxide (slaked lime, Ca(OH)2)

• Magnesium hydroxide (Mg(OH)2)

In agriculture to neutralise acidic soils

• Used in indigestion tablets as an antacid

• Substance which neutralises excess stomach acid

H+(aq) + OH-(aq) → H2O(l)

'Barium Meals'

Barium sulfate is opaque to X-rays - won't pass though it

Diagnose problems with oesophagus, stomach or intestines

1. Patient swallows barium meal

2. Barium sulfate coats tissues, making them show up on X-rays, showing structure of organs

To extract titanium from its ore

1. Main titanium ore (TiO2) is converted to titanium(IV) chloride (TiCl4) by heating it with carbon in steam of chlorine gas

2. Titanium chloride is then purified by fractional distillation

3. Then reduced by magnesium in furnace at 1000°C

CaO(s) + SO₂(g) → CaSO₃(s)

When acidic sulfur dioxide is removed from flue gases by reacting with an alkali

Powdered calcium oxide (CaO, lime) and calcium carbonate (CaCO3, limestone)

1. Slurry is made by mixing calcium oxide or calcium carbonate with water

2. The sprayed onto flue gases

3. Sulfur dioxide reacts with alkaline slurry and produces solid waste product, calcium sulfite

CaCO₃(s) + SO₂(g) → CaSO₃(s) + CO₂(g)

TiCl₄(g) + 2Mg(l) → Ti(s) + 2MgCl₂(l)

Barium sulfate is insoluble ∴ non-toxic

• Increases in no. of shells/increased sheilding

• Decreased attraction for bonding electrons

Ca(s) + H2O(l) → Ca2+(aq) + 2OH-(aq) + H2(g)

steam

• White light

• White powder

Mg + H2O → MgO + H2