Reactions of Group 2 Elements

The Elements of Group 1 and 2

Which Group 2 elements are covered in these reactions?

Magnesium, calcium, strontium and barium.

What three substances do Group 2 elements react with in this topic?

Oxygen, chlorine and water.

How does reactivity change down Group 2?

Reactivity increases down the group.

What is observed when magnesium burns in air?

It burns with a very bright white flame and forms a white solid.

What is the white solid formed when magnesium burns in air?

Magnesium oxide, MgO.

What is the equation for magnesium reacting with oxygen?

2Mg(s) + O₂(g) → 2MgO(s)

How do Group 2 reactions with oxygen change down the group?

They become more vigorous down the group.

How do calcium, strontium and barium react with oxygen compared with magnesium?

They react more vigorously because reactivity increases down Group 2.

Why may the increasing vigour of Group 2 metals burning in air be difficult to observe?

The metals may not be burning in identical conditions.

What happens if Group 2 metals are burned in a gas jar of oxygen?

The same oxidation reaction occurs but much more vigorously.

Do Group 2 metals react with oxygen when they are not heated?

Yes, they react slowly with oxygen when exposed to air.

What forms on the surface of Group 2 metals when exposed to air?

A surface coating of metal oxide.

How can the oxide coating affect further reaction?

It can help protect the metal from further reaction.

Which Group 2 metal in this section is the most reactive?

Barium.

Why is barium often stored under oil?

To prevent it reacting with oxygen and water vapour in the air.

What is the general equation for Group 2 metals reacting with oxygen?

2M(s) + O₂(g) → 2MO(s)

What ions are present in Group 2 metal oxides?

M²⁺ and O²⁻ ions.

What is the equation for calcium reacting with oxygen?

2Ca(s) + O₂(g) → 2CaO(s)

What happens when Group 2 metals are heated in chlorine gas?

They react to form metal chlorides.

How do Group 2 reactions with chlorine change down the group?

They become more vigorous down the group.

What is the general equation for Group 2 metals reacting with chlorine?

M(s) + Cl₂(g) → MCl₂(s)

What ions are present in Group 2 metal chlorides?

M²⁺ and Cl⁻ ions.

What is the equation for magnesium reacting with chlorine?

Mg(s) + Cl₂(g) → MgCl₂(s)

What is the equation for strontium reacting with chlorine?

Sr(s) + Cl₂(g) → SrCl₂(s)

How does magnesium react with cold water?

Very slowly, and the reaction does not proceed completely.

How do calcium, strontium and barium react with water?

They react with increasing vigour down the group.

What observation shows that magnesium reacts with cold water?

The magnesium becomes covered with bubbles of hydrogen gas.

What is observed when calcium reacts with water?

It becomes covered with bubbles of hydrogen and reacts vigorously.

What causes the increased effervescence down Group 2 when reacting with water?

Reactivity increases down the group, so hydrogen gas is produced more rapidly.

What products are formed when Group 2 metals react with cold water?

Hydrogen gas and a metal hydroxide.

What is the general equation for a Group 2 metal reacting with water?

M(s) + 2H₂O(l) → M(OH)₂(aq) + H₂(g)

What ions are present in Group 2 hydroxides?

M²⁺ and OH⁻ ions.

What is the equation for calcium reacting with water?

Ca(s) + 2H₂O(l) → Ca(OH)₂(s) + H₂(g)

Why is Ca(OH)₂ shown as a solid in the reaction of calcium with water?

Calcium hydroxide is only slightly soluble in water, so a precipitate forms.

Why does the liquid become cloudy when calcium reacts with water?

A precipitate of slightly soluble calcium hydroxide forms.

What is the equation for barium reacting with water?

Ba(s) + 2H₂O(l) → Ba(OH)₂(aq) + H₂(g)

Why is Ba(OH)₂ shown as aqueous while Ca(OH)₂ is shown as solid?

Barium hydroxide is soluble in water, whereas calcium hydroxide is only slightly soluble.

What happens to the solubility of Group 2 hydroxides down the group?

Solubility increases down the group.

How does magnesium react with steam?

It reacts rapidly and vigorously to form magnesium oxide and hydrogen.

What products form when magnesium reacts with steam?

Magnesium oxide and hydrogen gas.

What is the equation for magnesium reacting with steam?

Mg(s) + H₂O(g) → MgO(s) + H₂(g)

How does magnesium's reaction with steam differ from its reaction with cold water?

Magnesium reacts very slowly with cold water but rapidly and vigorously with steam.

What solid is formed when magnesium reacts with steam?

White magnesium oxide, MgO.

Why is the hydrogen produced in the magnesium and steam experiment burned as it leaves the tube?

To prevent highly flammable hydrogen gas escaping into the laboratory.

Why should water not be used to put out a burning magnesium fire?

Hot magnesium can react with water or steam to produce flammable hydrogen gas, which could make the fire more dangerous.

Do you need to know the specific reactions of beryllium and radium for this topic?

No.

How does beryllium's reactivity compare with magnesium?

Beryllium is less reactive than magnesium.

How does radium's reactivity compare with barium?

Radium is more reactive than barium.

Why can the reactivity of beryllium and radium be predicted?

Reactivity increases down Group 2.

What is the key trend for Group 2 reactions with oxygen, chlorine and water?

The reactions become more vigorous down the group because reactivity increases.