Group 2, the alkaline earth metals PDF

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Group 2: The alkaline earth metals    

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All of the group 2 elements have 2 electrons in an outer s-orbital. Trends As you go down group 2, the atomic radius will increase as each element will have an extra main level of electrons compared to the previous element. Each period adds an extra shell of electrons. The s orbital containing the outer 2 electrons of each group 2 element, will get increasingly further away from the nucleus as you go down the group. This means that the first ie of the alkaline earth metals will decrease down the group as the outer most electron is further awa from the nucleus so less strongly attracted as well as becoming more and more shielded due to extra shells of electrons between it and the nucleus. All the group 2 elements will always form a 2+ ion. This means that for complete ionisation you need the first ionisation energy plus the second ionisation energy. All group 2 elements are metals with high boiling points due to their large metallic structure. As you go down the group, the strength of the metallic bond will decrease as the sea of delocalised electrons will be getting further away from the nucleus. In turn the boiling point of the metal will decrease as you go down the group as it takes less energy to break the metallic bonds apart. In all reactions, the group 2 metals get more reactive as you go down the group. REACTIONS WITH WATER During their chemical reactions with water, the group 2 metals all oxidise to go from an Ox of 0 to +2 Their reactivity with water, the metals get more reactive as you go down the second group. An example of a reaction is Mg + 2H2O  Mg(OH)2 + H2. This is what is formed when magnesium will react with cold water. When reacting with hot water or steam the following reaction occurs Mg + H2O  MgO + H2. Magnesium reacts more vigorously with hot water or steam than with cold water as do all the other group 2 elements. All the reactions with water are exothermic and become increasingly exothermic as you go down group 2 SOLUBILITY Solubility of hydroxides All of the group 2 metal hydroxides (Mg-Ba) are white solids and their solubility will increase as they go down the group. Due to this, Mg(OH)2 is almost completely insoluble The calcium hydroxide formed from the reaction of calcium and cold water is used to treat acidic soil as different crops prefer different Ph conditions. Magnesium hydroxide, also known as ‘milk of magnesia’ is used in medicine to neutralise excess stomach acid which can cause indigestion. Solubility of sulphates The trend in the solubility of sulphate is the complete opposite. From Mg to Ba, the group 2 sulphates become less soluble. Barium sulphate is virtually insoluble Due to its high insolubility, barium sulphate is used to outline the gut in medical examinations as it is very good at absorbing xrays. Barium compunds are toxic however because barium sulphate I so insoluble this method is completely safe

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Acidified BaCl2 is used as a reagent to test for sulphates. The acid is there to remove any impurities which could form carbonate of hydroxide ions which would also give precipitates. The reason BaCl2 is used is that the barium sulphate precipitate formed is completely insoluble unlike the other group 2 sulphates....