Module 2 Chem Group 2 Elements

Trend in atomic radius down Group 2

Atomic radius INCREASES.

Trend in 1st Ionisation energies down Group 2

1st Ionisation energies DECREASE.

Trend in melting points down Group 2

Melting points DECREASE.

Why do group 2 elements have high melting points?

They have a giant metallic lattice structure with strong electrostatic forces of attraction between positive metal ions and delocalised electrons which take lots of energy to break.

Why do group 2 elements all react in similar ways?

They all have two outer electrons.

What do group 2 compounds look like?

Most are white crystalline solids

Why does atomic radius increase down group 2?

More shells of electrons.
More shielding by inner shells.
Less attraction between the nucleus and the outer shell of electrons.

Why does first ionisation energy decrease down group 2?

Atomic radius increases
More shells with more shielding
Weaker attraction between the nucleus and the electron being removed.

Why does the melting points decrease down group 2?

Ions get larger

Why does reactivity increase down group 2?

Atomic radius decreases
More shielding
Weaker nuclear attraction on the outer electrons so they are lost more easily

What observation is seen when magnesium reacts with cold water?

Very slow reaction with a few bubbles of H₂ forming on the surface of the metal.

What is the equation for the reaction of magnesium with cold water?

Mg + 2H₂O → Mg(OH)₂ + H₂

What observation is seen when magnesium reacts with steam?

Bright white light/flame and a white solid is produced.

What is the equation for the reaction between magnesium and steam?

Mg + H₂O → MgO + H₂

What is the observation when reacting calcium with cold water?

Effervescence and a white solid forms as Ca(OH)₂ is only slightly soluble (forms an alkali solution)

What is the equation for the reaction of calcium with cold water?

Ca + 2H₂O → Ca(OH)₂ + H₂

What is the equation for the reaction of strontium with cold water?

Sr + 2H₂O → Sr(OH)₂ + H₂

What observation is seen when strontium reacts with cold water?

Effervescence

What observation is seen when barium reacts with cold water?

Effervescence

What is the equation for the reaction of barium with cold water?

Ba + 2H₂O → Ba(OH)₂ + H₂

How is magnesium used to extract titanium from its ore?

The ore is reacted with carbon and chlorine
TiO₂ + C + 2Cl₂ → TiCl₄ + CO₂
Then is reduced with magnesium
TiCl₄ + 2Mg → Ti + 2MgCl₂

What is the trend in solubility for group 2 hydroxides?

Solubility increases down the group

What are the uses of magnesium hydroxide in medicine?

Indigestion tablets and 'milk of magnesia' which help to neutralise stomach acid

What is the use of calcium hydroxide in agriculture?

Neutralises acidic soils

What is the trend in solubility for group 2 sulfates?

The solubility decreases down the group

How can the presence of Mg²⁺ ions be confirmed?

Add aqueous NaOH to the solution.
If Mg is present a white precipitate of Mg(OH)₂ forms.

How can the presence of Ba²⁺ ions be confirmed?

Add H₂SO₄ or Na₂SO₄ to a solution.
If barium is present a white precipitate of BaSO₄ forms.

What is the test for sulfate ions?

Take 1cm³ of solution of the unknown.
Add 1cm³ of HCl to remove other ions that interfere with the test eg CO₃²⁻.
Add 1cm³ of BaCl₂.
If sulfate ions are present a white precipitate of BaSO₄ forms.

What is the use of barium sulfate in medicine?

Used in barium meal - BaSO₄ can absorb x rays which allows soft tissue to be seen.

Why is barium sulfate safe to use in medicine?

BaSO₄ is insoluble so won't be absorbed into the blood - barium ions are toxic

What is flue gas desulfurisation?

CaO and CaCO₃ are basic and can be used to remove acid oxides such as SO₂ from power station chimneys

What are the flue gas desulfurisation equations?

CaO + SO₂ → CaSO₃
CaCO₃ + SO₂ -> CaSO₃ + CO₂