group 2

• Give the equation for magnesium and liquid water

  Mg + 2H2O -> Mg(OH)2 + H2
• Give the equation for magnesium and steam

  Mg+ H2O -> MgO + H2
• The reactivity of Group 2 elements increases down the group.This is because, as we move down the group…

  • the attraction an outer electron experiences towards the nucleus decreases
  •  second ionisation energies decrease
• Which compounds are used to treat indigestion?

  Mg(OH)2 and CaCO3
• When Group 2 elements react with water, they undergo a redox reaction and form an aqueous metal hydroxide
• Group 2 element's reaction with water becomes more vigorous as we move down the group
• Group 2 elements react with a dilute acid to form a soluble salt and hydrogen gas
• Down the group of group 2 elements, reactivity with dilute acid increases
• As we move down group 2, the outer electrons are...

  • more shielded
  • further away from nucleus
• Down a group 2 first and second ionisation energy decrease
• Why does reactivity increase from Mg to Ba?

  1. Down a group, shielding increases
  2. The outer electrons experience less attraction towards the nucleus
  3. This causes a decrease in the first and second ionisation energies
• When a group 2 element reacts with a dilute acid, the observable features are:

  • Effervescence (because bubbles of hydrogen gas are released)
  • The solid metal disappears over the course of the reaction (because it’s turning into a salt that dissolves in solution)
• Trend: The group 2 elements become more reactive down the group.

  Explanation: As we move down group 2, the outer electrons are more shielded and further away from the nucleus. This means that the outer electrons experience less attraction towards the nucleus. So, there is a decrease in the first and second ionisation energies, which increases reactivity.
• metal oxide + water -> metal hydroxide
• Down group 2 hydroxides, solubility increases
• Magnesium hydroxide is hardly soluble at all and so can be observed as a white precipitate
• Metal hydroxides are bases so the pH of their solutions are alkaline
• In solution, alkalis release hydroxide ions
• As we move from our solution of Mg(OH)2​​​ down to Ba(OH)2​,​​ the pH of the solutions increase
• Magnesium hydroxide is used to cure heartburn because it is a base strong enough to neutralise the pH​ of the stomach.

  It's very low solubility in water, however, means that it is not strong enough to damage the body.
• Ca(OH)2 releases fewer hydroxide ions into solution than Sr(OH)2 does. So, we would expect Ca(OH)2 to have a lower pH.
• All group 2 oxides dissolve in water to form an alkaline solution of metal hydroxide. Therefore, the solutions have a pH greater than 7.
• Antacids usually contain Mg(OH)2 and CaCO3. They neutralise stomach acid to relieve symptoms of acid reflux / heartburn.
• Ca(OH)2 is used to raise the pH of acidic soils, in order to improve plant growth
• Ca(OH)2 is more soluble than Mg(OH)2 so has a higher pH and is a more powerful base. It is useful for agriculture but would be dangerous in the body.
• Barium sulfate is almost insoluble. This means that almost none of it will get absorbed into the gut, so it’s the perfect thing to eat to prepare for a gastro-intestinal x-ray!