Group 2

• If an atom or ion is reduced, what happens to the oxidation number?


  It decreases
• If an atom or ion is oxidised, what happens to the oxidation number?


  It increases
• What is the oxidation number of atoms in an uncombined element?


  0
• What is the oxidation number of neutral molecules?


  0
• What is the oxidation number of an ion?


  Usually, the same as its charge
• What is the oxidation number of oxygen?


  -2
• What is the oxidation number of group 1 metals?


  +1
• What is the oxidation number of group 2 metals?


  +2
• What is the oxidation number of hydrogen?


  +1
• What is the oxidation number of fluorine?


  -1
• What is the oxidation number of chlorine?


  -1
• Are there any exceptions to the oxidation number of oxygen being -2?


  Yes, in peroxides (H₂O₂) and in molecules with fluorine
• Are there any exceptions to the oxidation number of hydrogen being +1?



  Yes, in metal hydrides where it is -1
• Are there any exceptions to the oxidation number of fluorine being -1?



  No
• Are there any exceptions to the oxidation number of chlorine being -1?


  Yes, in compounds with oxygen or fluorine
• What oxidation number will the more electronegative atom of a molecule have?


  A negative oxidation number
• Why are group 2 elements reducing agents?


  Because in a redox reaction they lose two electrons which another element gains, which means that element has been reduced
• When group 2 elements react with oxygen, what product is formed?


  A white metal oxide powder
• What is the equation for the reaction between magnesium and oxygen?

  2Mg (s) + O₂ (g) ➞ 2MgO (s)
• What is the equation for the reaction between barium and water?

  Ba (s) + 2H₂O (l) ➞ Ba(OH)₂ (aq) + H₂ (g)
• How does reactivity change in group 2?

  Reactivity increases down the group because the atomic radius and electron shielding increases so, despite the nuclear charge increasing, the outer electrons experience a weaker attraction to the nucleus and are easier to remove.
• How does the melting and boiling points change in group 2? 


  The melting and boiling points decrease because the atomic radius and electron shielding increases, despite the nuclear charge increasing, the outer electrons experience a weaker attraction to the nucleus and the electrostatic attraction requires less energy to overcome.
• How does the ionisation energy change in group 2? 


  The ionisation energies decrease down the group because the attraction between the nucleus and outer electrons decreases, because of the increased atomic radius and electron shielding, making the outer electrons easier to remove.
• What is the equation for the first ionisation energy of magnesium?


  Mg (g) ➞ Mg⁺ (g) + e⁻
• What is the equation for the second ionisation energy of magnesium?


  Mg⁺ (g) ➞ Mg²⁺ (g) + e⁻
• How soluble are group 2 metal ?


  They are sparingly soluble with water
• What observation can be made when a solution of water and group 2 metal hydroxide becomes saturated?


  A white precipitate forms
• What is the equation for the reaction between calcium hydroxide and water?

  Ca(OH)₂ + H₂O (l) ➞ Ca²⁺ (aq) + 2OH⁻ (aq)
• When magnesium reacts with steam, what product is made and why?


  MgO because initially Mg(OH)₂ is formed but it decomposes in the heat
• How does the solubility change in group 2 hydroxides?

  Solubility increases down the group because the ionic bond strength decreases due to the decreased charge density which is because of the increased ionic radius, so less energy is needed to overcome the ionic bonds (which needs to be compensated when the bonds with the water form)
• How does the alkalinity change in group 2? 


  Alkalinity increases because more aqueous hydroxide ions are released into the solution because of the decreased ionic bond strength (which requires less energy to overcome)
• What is the pH of magnesium hydroxide?


  10
• What is the pH of calcium hydroxide?


  12
• What is the pH of barium hydroxide?


  13
• What is calcium hydroxide used for in farming?


  It's added to fields to neutralise acid in soil:

  Ca(OH)₂ (s) + 2H⁺ (aq) ➞ Ca²⁺ (aq) + 2H₂O (l)
• What is magnesium hydroxide or calcium carbonate used for in medicine?


  In antacids to neutralise the hydrochloric acid in stomach acid:

  Mg(OH)₂ (s) + 2HCl (aq) ➞ MgCl₂ (aq) + 2H₂O (l)

  CaCO₃ (s) + 2HCl (aq) ➞ CaCl₂ (aq) + H₂O (l) + CO₂ (g)
• What is reduction?

  • Gain of electrons
  • Removal of oxygen
  • Decrease in oxidation number
• What is oxidation?

  • Loss of electrons
  • Addition of oxygen
  • Increase in oxidation number