group 2

• The Group 2 elements react with oxygen, water and dilute acids.
• The reaction of all metals with oxygen follows the general equation: 2M (s) + O (g) → 2MO (s) where M is any metal in Group 2.
• Sr and Ba also form MO when reacting with oxygen.
• The reaction of all metals with water follows the general equation: M (s) + 2H O (l) → M(OH) (s) + H (g) with exceptions Be which does not react with water and Mg which forms MgO (s) and H (g).
• The reaction of all metals with dilute HCl follows the general equation: M(s) + 2HCl(aq) → MCl (aq) + H (g) with exceptions Mg which forms MgO (s) and H (g).
• The reaction of all metals with dilute H SO follows the general equation: M(s) + H SO (aq) → MSO (aq) + H (g) with exceptions CaSO , SrSO and BaSO which are insoluble.
• Learn the general equation for the reaction with oxygen, water and dilute HCl/H SO and the exceptions instead of memorizing the entire table.
• The higher the concentration of OH ions formed, the more alkaline the solution.
• When the metal oxides react with water, a Group 2 hydroxide is formed.
• The solubility of the Group 2 sulfates decreases going down the group.
• Going down the group, the solubility of these hydroxides increases, which means that the concentration of OH ions increases, increasing the pH of the solution.
• The alkalinity of the formed solution can therefore be explained by the solubility of the Group 2 hydroxides.
• The solubility of the Group 2 hydroxides decreases going down the group.
• When the oxides are dissolved in water, the following ionic reaction takes place: O(aq) + H2O(l) → 2OH(aq).
• As a result, going down the group, the alkalinity of the solution formed increases when Group 2 oxides react with water.
• Going down the group, the solutions formed from the reaction of Group 2 oxides with water become more alkaline.
• The hydroxides dissolve in water as follows: X(OH) (aq) → X(aq) + 2OH (aq).
• As a result of this, the elements become more reactive going down the group as it becomes easier for the atoms to lose two electrons and become 2+ ions.
• All Group 2 carbonates will form soluble chloride salts, water and carbon dioxide gas when reacted with dilute hydrochloric acid.
• The Group 2 ionisation energies decrease going down the table.
• Going down the group, the metals become more reactive.
• Going down the group, it becomes easier to remove the outer two electrons of the metals.
• Going down the group, the elements become larger as the outer two electrons occupy a new principal quantum shell which is further away from the nucleus.
• All elements in Group 2 (also called alkali earth metals) have the two electrons in their outermost principal quantum shell.
• The second ionisation energy is the energy needed to remove the second outer electron of an atom.
• The first ionisation energy is the energy needed to remove the first outer electron of an atom.
• The higher the charge and the smaller the ion, the higher the polarising power.
• The small positive ion attracts the delocalised electrons in the carbonate ion towards itself.
• The nuclear charge on the nucleus increases going down the group due to more protons, but factors such as an increased shielding effect and a larger distance between the outermost electrons and the nucleus outweigh the attraction of the higher nuclear charge.
• The more polarised they are, the more likely they are to thermally decompose as the bonds in the carbonate and nitrate ions become weaker.
• All Group 2 metals can form ionic compounds in which they donate these two outermost electrons to become an ion with +2 charge, thus oxidising themselves.
• Group 2 carbonate reactions with dilute acids include carbonate + dilute hydrochloric acid → salt + water + carbon dioxide, and carbonate + dilute sulfuric acid → sulfate + water + carbon dioxide.
• When reacted with sulfuric acid, the carbonates of Ca, Sr and Ba form an insoluble sulfate layer on their surface which stops any further reaction after the initial bubbling of carbon dioxide gas is seen.
• Reactions of group 2 carbonates include forming soluble chloride salts, water and carbon dioxide gas when reacted with dilute hydrochloric acid, and forming soluble chloride salts, water and sulfur dioxide gas when reacted with dilute sulfuric acid.
• Going down Group 2, more heat is needed to break down the carbonate and nitrate ions.
• Group 2 carbonates break down (decompose) when heated to form the metal oxide and give off carbon dioxide gas.
• The general equation for the decomposition of Group 2 carbonates is: XCO (s) + HEAT → XO (s) + CO (g), where X is a Group 2 element.
• The smaller positive ions at the top of the groups will polarise the anions more than the larger ions at the bottom of the group.
• The thermal stability of the Group 2 carbonates and nitrates therefore increases down the group.
• All Group 2 carbonates (except for BeCO) are insoluble in water.