3.2.2 Group 2, the alkaline earth metals

• Group 2: Atomic radius

  The atomic radius increases down the group

  The nuclear charge increase as the number of protons increases

  The shielding increases as there are more energy levels

  Therefore electrons are attracted less strongly

  Therefore the atomic radius increases
• Group 2: First ionisation energy

  The first ionisation every decreases as you go down G2

  > As you go down a group the atoms get bigger

  > The distance between the nucleus and the outer electron increase

  > The outer electron is more shielded from the nucleus

  > The outer electron is less strongly attracted to the nucleus and more easily removed

  > Therefore less energy is needed to remove the outer election
• Group 2 : Melting Points

  > The melting point of the elements decreases down the group

  > All the ions in group 2 have a +2 charge

  > As we go down group 2 the size of the ion increases more sheilding/ more electron shells.

  > The 2+ charge is spread over a large area therefore the charge density decreases.

  > There is a weaker electrostatic force between the larger ions and the sea of delocalised elections.

  > Therefore less energy is needed to overcome the force of attraction so melting point decreases.
• Group 2: Reaction with Water

  Solubility increases down the group

  > Beryllium does not react with water or steam

  Mg:

  Mg + H2O -> Mg(OH)2 + H2

  Magnesium hydroxide is sparingly soluble. Forms a white precipitate.

  Magnesium reacts with steam to form MgO and Hydrogen

  Ca:

  Ca + H2O -> Ca(OH)2 + H2

  Calcium reacts steadily with water and is slightly soluble.
• Group 2: Reaction with Water

  Sr:

  Sr + H2O -> Sr(OH)2 + H2

  Strontium reacts quickly with water. Stored in oil to prevent reaction with water vapour.

  Ba:

  Ba + H2O -> Ba(OH)2 + H2

  Barium reacts quickly with water. Stored in oil to prevent reaction with water vapour.
• Uses of group 2 hydroxides:

  Mg(OH)2 :

  Magnesium Hydroxide is used as an antacid used to treat indigestion by neutralising excess stomach acid.

  Ca(OH)2:

  Calcium hydroxide is used in agriculture to control the acidity of the soil.
• Uses of Group 2 Sulfates:

  Barium Sulfate is used as a contrast medium for X-rays as it is so insoluble so it doesn't allow X-rays to pass through.
• Test for Sulfate ions

  Reagent(s): Add Hydrochloric acid and Barium Chloride

  Observation: White precipitate

  You add HCl to remove ions (CO3^2-) that could interfere with the test and produce a precipitate and give a false result.

  Test for hydroxide ions in MgCl2

  Reagents(s): Sodium Hydroxide

  Observation: White Precipitate
• Extraction of Titanium:

  Titanium cannot be extracted using carbon as Titanium carbide is brittle.

  Step 1:

  Titanium (IV)oxide is change to TiCl4 using Cl2 gas and Coke, 900°C

  Eq: TiO2 + 2C + 2Cl2 -> TiCl4 + 2CO

  Step 2:

  Titanium chloride is then reduce by a metal high in the reactivity series e.g. Mg. Argon is used to provide an inert atmosphere to prevent Mg reacting with oxygen.

  TiCl4 + 2Mg -> Ti + 2MgCl2

  Titanium is expensive as a result of the reactions