Group 2, the alkaline earth metals

• Group 2 elements

  Have two electrons in the outermost shell
• The metallic radius of group 2 elements increases down the group. This is because a new shell away from the nucleus is filled as we go down the group.
• Group 2 elements

  Lose two electrons in its outermost shell to attain the stable configuration. They form 2+ ions.
• Successive ionisation energy is always greater than the 1st ionisation energy
• The reactivity of group 2 elements increases down the group due to decrease in ionisation energy.
• Reaction of group 2 metals with oxygen

  1. Group 2 metals burn in air to form solid metal oxides

  2. The solid metal oxides formed are white in colour

  3. The group 2 metal oxides are basic in nature
• Reaction of group 2 metals with water

  1. Group 2 metals react with water to form hydroxides and releases hydrogen gas

  2. Magnesium reacts very slowly with cold water to form magnesium hydroxide and hydrogen gas

  3. Hot magnesium reacts with steam vigorously producing a bright light and forming magnesium oxide and hydrogen gas

  4. Calcium is more reactive with water than magnesium. When calcium reacts with water, a white suspension of calcium hydroxide is formed and hydrogen gas is released
• Reaction of group 2 metals with acids

  1. Group 2 metals react with acids to form salt and hydrogen

  2. Reaction with hydrochloric acid forms chlorides, reaction with nitric acid forms nitrates and reaction with sulphuric acid forms sulphates
• Titanium

  A transition metal that is less dense, less corrosive and has high strength. Due to these properties its alloys are widely used in aircrafts and submarines.
• Titanium cannot be reduced with carbon because titanium carbide (TiC) is formed when titanium reacts with carbon and the presence of TiC tends to make the metal brittle.
• Titanium is expensive because the extraction of magnesium from its ore is expensive.
• Extraction of titanium is a slow process and energy intensive.
• Uses of group 2 compounds

  • Magnesium hydroxide is used in indigestion remedies to neutralise the excess acid in stomach.
  • Calcium hydroxide (know as slaked lime) is used to neutralise the acidity in soils.
  • Calcium carbonate is used for manufacturing cement. Calcium carbonate is heated to form calcium oxide. Calcium oxide is then roasted with clay to form cement.
  • The pollutants released from burning of fuels is passed through a scrubber containing calcium oxide to remove sulphur dioxide. Basic calcium oxide neutralises the acidic sulphur dioxide.
  • Calcium sulphate is used to make plasterboards.
  • Barium chloride with hydrochloric acid is used to test the presence of sulphates. Barium ions (Ba2+) react with sulphate ions (SO42-) and white barium sulphate is produced.
  • Barium absorbs X-rays. This property is used in the field of medicine to X-ray intestine.
• Barium sulphate is insoluble in water and thus, appears to be a white precipitate. This reaction is used as test for sulphate ions in unknown compounds.
• Even though barium is toxic, barium sulphate is safe as it is insoluble in water and is not absorbed into patient's body.
• Trend in boiling point in group 2

  • decreases down the group
  • Down the group, the atomic size increases.
  • The distance between metal ions and delocalised electrons increases.
  • The electrostatic force of attraction between metal ions and delocalised electrons reduces.
• Describe the bonding in magnesium (2)

  • attraction between Mg2+ ions
  • and delocalised electrons
• Explain why the melting point of magnesium is higher than the melting point of sodium (2)

  • Mg2+ has a higher charge than Na+/Mg2+ ions are smaller
  • stronger attraction to delocalised sea of electrons
• Explain, in terms of structure and bonding, why magnesium chloride has a high melting point (3)

  • giant ionic lattice
  • strong electrostatic forces of attraction
  • between Mg2+ and Cl- ions
• Explain why the melting point of calcium sulfate is high (2)

  • strong attraction
  • between positive and negative ions
• The ionisation energy decreases down group 2 because of:

  • Increase in the size of the atom
  • Decrease in force of attraction between nucleus and valence electrons
  • Increase in shielding effect of inner filled shells
• Explain why the second ionisation energy of calcium is lower than the second ionisation energy of potassium (2)

  • Ca+ outer electron is further from nucleus
  • more shielding
• The pH of hydroxide solutions increases down the group. This is because of the solubility of hydroxides in water increases down the group.
• Give the formula of the hydroxide of the element in group 2, from Mg to Ba, that is least soluble in water

  • Mg(OH)2
• Hot magnesium reacting with steam equation

  Mg (s) + H2O (g) → MgO (s) + H2 (g)
• Magnesium reacting with cold water equation

  Mg (s) + 2H2O (l) → Mg(OH)2 (aq) + H2 (g)
• State the trend in solubility, in water, of the Group 2 sulfates from magnesium to barium (1)

  • decreases
• Group 2 chlorides will react with sodium hydroxide to form a group 2 hydroxide. The solubility of the hydroxide formed will increase going down the group, with magnesium hydroxide forming a white precipitate.
• The solubility of sulphates of group 2 elements in water decreases down the group.
• The reaction of barium and sulphuric acid is slowed down as barium sulphate which is insoluble in water covers the surface of metal.

  Ba (s) + H2SO4 (aq) → BaSO4 (s) + H2 (g)
• State what is observed when dilute aqueous sodium hydroxide is added to separate solutions of magnesium chloride and barium chloride. (2)

  1. Observation with magnesium chloride: white precipitate
  2. Observation with barium chloride: no visible change
• Extraction of Titanium using magnesium

  1. Titanium oxide is converted to titanium(IV) chloride by heating it with chlorine and coke (a form of carbon) at 1000 ⁰C
  2. Titanium(IV) chloride is converted to titanium in the presence of molten magnesium.

  TiCl4(l) + 2Mg(s) → Ti(s) + 2MgCl2(s)
• Give an equation for the reaction between titanium (IV) chloride and magnesium.

  State the role of magnesium in this reaction (2)

  1. TiCl4(l) + 2Mg(s) → Ti(s) + 2MgCl2(s)
  2. Magnesium is a reducing agent
• Give an equation to show magnesium is used as the reducing agent in the extraction of titanium.

  Explain, in terms of oxidation states, why magnesium is the reducing agent. (2)

  • TiCl4 + 2Mg → Ti + 2MgCl2
  • Mg changes oxidation state from 0 to +2 so electrons are lost
• Magnesium hydroxide is used in indigestion remedies to neutralise the excess acid in stomach.

  Mg(OH)2 (s) + 2HCl (aq) → MgCl2 (aq) + 2H2O (l)
• Calcium hydroxide (know as slaked lime) is used to neutralise the acidity in soils.
• The pollutants released from burning of fuels is passed through a scrubber containing calcium oxide or calcium carbonate to remove sulphur dioxide. Basic calcium oxide/carbonate neutralises the acidic sulphur dioxide.

  CaO + SO2 + 2H2O + 0.5O2 → CaSO3.2H2O

  CaCO3 + SO2 → CaSO3 + CO2
• Calcium sulphate is used to make plasterboards.
• Barium chloride with hydrochloric acid is used to test the presence of sulphates. Barium ions (Ba2+) react with sulphate ions (SO42-) and white barium sulphate is produced.

  • Barium sulphate is insoluble in water and thus, appears to be a white precipitate. This reaction is used as test for sulphate ions in unknown compounds.
  • Ba^2+ + SO4^2- → BaSO4
• Barium absorbs X-rays. This property is used in the field of medicine to X-ray intestine.

  • A patient is given a dose of barium sulphate before taking an X-ray.
  • The presence of barium will show the image of intestines.
  • Even though barium is toxic, barium sulphate is safe as it is insoluble in water and is not absorbed into patient’s body.