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 2.
• 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 being insoluble.
• 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 solubility of the Group 2 sulfates decreases going down the group.
• When the oxides are dissolved in water, the following ionic reaction takes place: O(aq) + H2O(l) → 2OH(aq).
• When the metal oxides react with water, a Group 2 hydroxide is formed.
• The alkalinity of the formed solution can therefore be explained by the solubility of the Group 2 hydroxides.
• As a result, going down the group, the alkalinity of the solution formed increases when Group 2 oxides react with water.
• The hydroxides dissolve in water as follows: X(OH) (aq) → X(aq) + 2OH (aq).
• The solubility of the Group 2 hydroxides decreases going down the group.
• Going down the group, the solutions formed from the reaction of Group 2 oxides with water become more alkaline.
• The higher the concentration of OH ions formed, the more alkaline the solution.
• As a result of this, the elements become more reactive going down the group as it gets easier for the atoms to lose two electrons and become 2+ ions.
• 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 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.
• All Group 2 metals can form ionic compounds in which they donate these two outermost electrons to become an ion with +2 charge, oxidising themselves in the process.
• The more polarised they are, the more likely they are to thermally decompose as the bonds in the carbonate and nitrate ions become weaker.
• The nuclear charge on the nucleus increases going down the group because there are 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 first ionisation energy is the energy needed to remove the first outer electron of an atom.
• 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.
• All Group 2 carbonates will form soluble chloride salts, water and carbon dioxide gas when reacted with dilute hydrochloric acid.
• 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.
• Group 2 carbonates break down (decompose) when heated to form the metal oxide and give off carbon dioxide gas.
• 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.
• 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.
• Going down Group 2, more heat is needed to break down the carbonate and nitrate ions.
• The thermal stability of the Group 2 carbonates and nitrates therefore increases down the group.
• 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.
• All Group 2 carbonates (except for BeCO) are insoluble in water.
• Radium’s outermost electrons are even further away than in barium and are therefore more easily removed making radium more reactive than barium.