2.2 - Group 2, the alkaline earth metals

What happens to the atomic radius as you go down group 2?

What happens to the atomic radius as you go down group 2?

• Increases down group

• Each element has an extra filled sub orbital of electrons than the element above

What is the trend for melting points down group 2?

• going down the group, the electrons in the “sea” of delocalised electrons are further away from the positive nuclei

• Strength of metallic bonds decreases going down the group

• Mg doesn’t fit the trend as it has the lowest MPT

What is the trend in first IE down G2?

• decrease down the group

• Takes less energy to remove electrons as they become further & further away from the positive nucleus

• Greater shielding as well

What’s the reaction of water with G2?

• metal gets more reactive going down the group

• form metal hydroxide and hydrogen

What is Mg(OH)2 used for?

• milk of magnesia

• Used in indigestion remedies

• Mg reacts very slowly with cold water

Magnesium + Steam

• MgO & O2

• Rapidly compared to cold water

Calcium + Water

• Calcium reacts more vigorously compared to beryllium and magnesium

• CaOH(called slaked lime - used to treat acidic soil) & H2 produced

Strontium/Barium + Water

• react even more vigorously compared to Mg,Be, Ca

• Form metal hydroxides and hydrogen

How does the solubility of group 2 compounds differ?

• singly charged negative ions e,g (OH-) increase down group

• Doubly charged negative ions e.g SO42- decrease down group

Solubility of G2 Hydroxides

Solubility of G2 sulfates

Why can this method not be used to extract titanium? What’s used instead?

Metal oxide + carbon —> metal + carbon dioxide

• titanium reacts with carbon to form titanium carbide, TiC which makes the metal brittle

• Titanium oxide reacts with chlorine and carbon to form titanium chloride, TiCl4 and CO

What’s the trend in the solubility of the hydroxides?

• going down the group, become more soluble

• Hydroxides are all white solids

• Magnesium hydroxide is almost insoluble (sold as a suspension in water)

• Calcium hydroxide is sparingly soluble and used as lime water

• Strontium hydroxide is more soluble

• Barium hydroxide dissolved to produce a strongly alkaline solution

What’s the solubility trend in the sulfates like?

• become less soluble down the group

• Barium sulfate is insoluble, can be taken as a barium meal in x-rays,

• Insolubility of BaSO4 is used in a simple test for sulfates

Test for sulfates & procedure

Why is acid added to the solution?

Uses of G2 compound

Why can the metal oxide + carbon not be used for titanium?