Group 2

• Group 2 metals form ions with a 2+ charge
• Group 2 metals react with water to form a metal hydroxide and hydrogen gas.
• The general equation for group 2 metals (M) reacting with water is M + 2H2O --> M(OH)2 + H2
• Group 2 metals get more reactive down the group because the outermost electrons are further from the nucleus, and so are more easily lost.
• When group 2 metals burn in oxygen, solid white oxides form.
• The general equation for the group 2 metals (M) burning in oxygen is 2M + O2 --> 2MO
• Group 2 oxides and hydroxides are bases.
• The oxides of group 2 metals react readily with water to form metal hydroxides, which dissolve. The hydroxide ions make these solutions strongly alkaline.
• The equation for the reaction of calcium oxide with water is: CaO + H2O --> Ca2+ + 2OH-
• All the group 2 oxides react readily with water except magnesium oxide which only reacts slowly and produces a not very soluble hydroxide.
• The oxides form more strongly alkaline solutions as you go down the group because the hydroxides get more soluble.
• Both the oxides and hydroxides neutralise dilute acids, forming solutions of the corresponding salts.
• The solubility of group 2 hydroxides increases down the group
• The solubility of group 2 carbonates and sulfates decreases down the group.
• Compounds like magnesium, hydroxide, which have very low solubilities, are said to be sparingly soluble.
• Thermal decomposition is when a substance breaks down (decomposes) when heated.
• Group 2 carbonates decompose to form the oxide and carbon dioxide.
• The general equation for the decomposition of a group 2 metal carbonate (M) is MCO3 --> MO + CO2
• The more thermally stable a substance is, the more heat is will take to break it down.
• Thermal stability of group 2 carbonates increases down the group.
• Anions are negatively charged ions, cations are positively charged ions.
• Carbonate ions are large anions and can be made unstable by the presence of a group 2 metal cation. The cation draws the electrons of the carbonate ions towards itself (it polarises it). This distorts the carbonate ion and the greater the distortion, the less stable the carbonate ion.
• Thermal stability of group 2 carbonates increases down the group because large cations cause less distortion than small cations as they have a lower charge density. So the further down the group, the larger the cations, the less distortion caused, and the more stable the carbonate anion.