Group 2

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  • Group 2
    • Trends
      • Electronic Configuration
        • Each elements configuration ends with s2 - they all have two electrons in the outer shell
      • Atomic Radii
        • The size increases down the group because extra shell are being added at increasing distance from the nucleus
          • The distance is further increased by greater shielding from inner shells and this outweighs the increasing nuclear charge, so the electrons are attracted less strongly and can be further from the nucleus
      • Ionisation Energies
        • On going down the group the ionisation energies decrease. This is because more shells of electrons are being added so outer electrons experience more shielding and are further from the nucleus. These two factors outweigh the increasing nuclear charge so attraction to the nucleus decreases
        • The decreasing first and second ionisation energies explain why the reactivity of the elements increases going down the group
          • The elements have to be ionised in order to react and form compounds. Decreasing ionisation energies mean decreasing activation energies and faster reactions. Less energy is needed to make the atoms into ions, so they react more readily to become ions
    • Reactions of the Group 2 Elements
      • With oxygen
        • The elements burn vigorously. The reactions become more vigorous on going down the group as the ionisation energies of the elements decrease and they react more easily
      • With Water
        • React vigorously and form Hydrogen gas
      • With Acids
        • React to form hydrogen and a solution of the corresponding salt
    • Reactions of Group 2 Metal Oxides
      • With Water
        • When water is added to a group 2 oxide it will react to form the corresponding hydroxide
      • With Acids
        • The oxides dissolve in aqueous acid to form a solution of the corresponding salt and water
    • Reactions of Carbonates
      • Group 2 carbonates are insoluble in water so will always be a solid when reacting
      • With Acids
        • When reacting with an acid, the salt formed is insoluble
        • Dissolve rapidly in aqueous acid with vigorous effervescence, giving carbon dioxide
      • Thermal Decomposition
        • If a carbonate is heated strongly, it decomposes to evolve carbon dioxide and form the corresponding oxide
        • The thermal stability of the group two carbonates increases down the group - as you go down the group you need higher temperatures to decompose the carbonate
    • Uses of compounds of Group 2 Elements
      • Magnesium hydroxide is used in some indigestion tablets as an antacid as it neutralises excess acid in the stomach
        • As magnesium hydroxide is only very slightly soluble in water, there is no possibility of liquid in the mouth or stomach becoming dangerously alkaline
      • Calcium Hydroxide: Ca(OH)2 (slaked lime) is used in agriculture to neutralise acidic soils
    • Limestone and Lime
      • Mainly Calcium Carbonate (CaCO3). It can be decomposed by heating to form Calcium Oxide (quicklime)(and CO2)
        • Adding water to the calcium oxide forms calcium hydroxide - known as slaked lime and is used to neutralise water that is too acidic
          • A solution of calcium hydroxide is known as lime water. It is used in the laboratory for identifying carbon dioxide gas because the calcium hydroxide can react with CO2 to form insoluble calcium carbonate which makes the limewater look cloudy

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