Everything from the 3 lessons of this topic on a few pages: the key idea of each lesson, the diagram to remember, the points to learn and the traps examiners set. Read it, cover it, test yourself.
All Group 2 elements have two outer s electrons and form M2+ ions, so their compounds have oxidation number +2. Down the group the atoms gain shells, so atomic radius increases and shielding increases; the outer electrons are less strongly held, so the first and second ionisation energies decrease. Less energy is needed to form M2+, so reactivity increases from Mg to Ba. The metals burn in oxygen to form MO, react with water to give hydroxides and hydrogen (Mg only slowly unless it is steam), and react with dilute acids to form salts and hydrogen.
Calcium, strontium and barium react with dilute sulfuric acid at first but soon slow down, because their sulfates are insoluble and coat the metal. Do not use this to argue that reactivity decreases down the group. And magnesium with steam gives the oxide, not the hydroxide.
Group 2 carbonates decompose on heating to the oxide and carbon dioxide; nitrates decompose to the oxide, nitrogen dioxide and oxygen. Thermal stability increases down the group: the M2+ ion gets larger with the same charge, so its charge density falls and it polarises (distorts) the large carbonate or nitrate anion less. The hydroxides become more soluble down the group, so the pH of their saturated solutions rises; the sulfates become less soluble, so barium sulfate is insoluble, which is the basis of the test for sulfate ions.
The two solubility trends go in opposite directions: hydroxides become more soluble down the group, sulfates less. When explaining thermal stability, talk about the cation polarising the anion; the anion is the same throughout, so the change must come from the size of M2+.
Heating limestone (CaCO3) in a lime kiln gives quicklime (CaO) and CO2; adding water gives slaked lime (Ca(OH)2) in an exothermic reaction; Ca(OH)2 absorbs CO2 to re-form CaCO3, which is why limewater turns milky. Slaked lime and powdered limestone are bases used to neutralise acidic soils and lakes. Limestone is used in building and to make cement. Magnesium hydroxide is a mild base in indigestion remedies, and barium sulfate is safe to swallow for X-ray “barium meals” because it is insoluble.
Barium compounds in general are toxic. The barium meal is safe only because BaSO4 is insoluble; a soluble salt such as BaCl2 must never be used. And slaking quicklime is strongly exothermic: the mixture can boil, so water must be added carefully.