topic 02 - Group 2 (the alkaline earth metals)

• what are groups in the periodic table?

  columns of elements which all share the same trend in physical properties and similar chemical properties.
• what are he group 2 elements known as?

  the alkaline earth metals
• which group 2 elements do we focus on?

  • magnesium
  • calcium
  • strontium
  • barium
• how does atomic radius change descending group 2?


  atomic radius increases as you descend group 2.
• how does first ionisation energy change descending group 2?


  first ionisation energy decreases as you go down group 2.
• how can both atomic radius increasing descending group 2 and 1st ionisation energy decreasing descending group 2 be explained?

  • moving down group 2, there is an additional energy level of electrons added.
  • so an increase in the shielding effect and decrease in the force of attraction between protons in nucleus and outermost electrons.
  • outermost electrons are held less tightly to the nucleus and it takes less energy to remove them so a decrease in ionisation energy.
  • less force of attraction means outermost electrons aren't pulled in as tightly so increased atomic radius.
• how does melting point change as you descend group 2?


  melting point decreases as you descend group 2
• what are the 3 group 2 trends?

  • melting point decreases.
  • 1st ionisation energy decreases
  • atomic radius increases.
• explain the structure of group 2 elements

  • group 2 elements are all metals
  • they have a giant metallic lattice structure
  • the positively charges metal ions form metallic bonds with the surrounding delocalised electrons.
• what sort of ion does the group 2 elements become?

  positively charged metal cations with a 2+ charge
• how does size of ion change descending group 2?

  descending group 2, the size of ion increases
• explain why melting point decreases as you go down group 2?

  • as you go down group 2, the size of ions increases so charge:size ratio decreases.
  • the smaller the charge:size ratio, the weaker the metallic bonds formed so the lower the amount of energy to break the metallic lattice structure and the lower the melting point.
• what is the reactivity of an element?

  the reactivity of an element is determined by how easily the element loses or gains the number of electrons needed to achieve the stability of an outer shell.
• ... the more reactive the element?

  the easier it is for the element to lose of gain electrons, the more reactive the element.
• how do group 2 elements gain a full outermost shell?

  group 2 elements need to lose 2 electrons to achieve a full outermost shell
• how does chemical reactivity of the group 2 elements change as you descend?

  as you descend group 2, the chemical reactivity increases.
• explain why chemical reactivity increases as you go down group 2?

  • as you go down group 2, the 2 outer shell electrons get further away from the nucleus as atomic radius increases.
  • the force of attraction between these electrons and the protons in the nucleus gets weaker
  • so the electrons are more easily lost
• how an we show that chemical reactivity increases as you go down group 2?

  we use the reactions oft he group 2 elements with water
• how do group 2 elements react with water?

  • the group 2 elements react with water to produce a group 2 hydroxide and hydrogen gas.
  • general equation : M (s) + 2H2O --> M(OH)2 (aq/s) + H2 (s)
  • M = any group 2 metal
  • state symbol of the M(OH)2 depends on the solubility of the hydroxide formed.
• describe how magnesium reacts with water

  • magnesium reacts very slowly with cold water to produce solid Mg(OH)2 and gaseous H2.
  • equation : Mg (s) + 2H2O --> Mg(OH)2 + H2 (g)
• describe how magnesium reacts with steam

  • the reaction occurs vert quickly
  • MgO (s) is produced instead of the hydroxide.
  • equation : Mg (S) + H2O --> MgO (s) + H2 (g)
• how does the vigour of the reactions of the elements with water change as you go down group 2?


  as you move down group 2, the reactions of the elements with water increase in vigour
• describe how calcium reacts with cold water

  • calcium reacts with water more quickly to produce a solution of Ca(OH)2 and gaseous H2.
  • equation : Ca (s) + H2O (l) --> Ca(OH)2 (aq) +H2 (g)
• describe how strontium reacts with cold water

  • strontium reacts with cold water more quickly than Mg and Ca to produce a solution of Sr(OH)2 and gaseous H2.
  • equation : Sr (s) + 2H2O --> Sr(OH)2 (aq) + H2
• describer how barium reacts with cold water

  • barium reacts with cold water in the most vigorous reaction to produce a solution of Ba(OH)2 and gaseous H2
  • equation : Ba (s) + 2H2O (l) --> Ba(OH)2 (aq) + H2 (g)
• describe alkalinity of a solution

  • the alkalinity of a solution depends on the concentration of OH- ions released into the solution, this is determined by the solubility of the hydroxide.
  • the more soluble the hydroxide, the higher the concentration of OH- ions released into the solution and the more alkaline the solution becomes.
• how does the solubility of the group 2 hydroxides change as you down group 2?

  solubility increases as you move down group 2
• describe the solubility of Mg(OH)2

  • Mg(OH)2 is sparingly soluble
  • has the appearance of a white precipitate
  • a solution containing the Mg(OH)2 precipitate is slightly alkaline
  • a pH of between 9.00 and 10.00
  • is the least soluble group 2 hydroxide
• how can suspensions of Mg(OH)2 be used?

  • can be used in medicine to treat indigestion and neutralise excess stomach acid
• describe the solubility of Ca(OH)2

  • slightly soluble
  • forms a solution in which a small amount of white precipitate may be seen
  • a solution of Ca(OH)2 is more alkaline
  • a pH between 10.00 and 11.00
• how can Ca(OH)2 be used?


  • can be used in agriculture to neutralise soil activity
• describe the solubility of Sr(OH)2

  • slightly soluble
  • forms a solution in which a small amount of white precipitate may be seen
  • more alkaline
  • a pH between 11.00 and 12.00
• describe the solubility of Ba(OH)2

  • soluble
  • forms a colourless solution
  • solution of Ba(OH)2 is the most alkaline
  • pH between 13.00 and 14.00
• how do the group 2 cations react with sulfate ions?

  they react to produce group 2 sulphates
• what is the formula for sulphate

  SO4 2-
• what its the general equation for the group 2 cations reaction with sulfate ions?

  • M2+ (aq) + So4 2- (aq) --> MSO4 (aq/s)
  • M = any group 2 metal
  • the state symbol of the MSO4 depends on the solubility of the sulfate formed
• how does the solubility of the group 2 sulphates change as you go down group 2?


  solubility of the sulphates decreases down group 2
• describe the reaction between manegsium and a sulphate ion

  • when a solution containing Mg2+ ions is added to a solution contains So4 2- ions
  • a colourless solution containing MgSO4 is formed
  • MGSO4 is soluble so to precipitate is formed
  • equation : MG2+ (aq) + So4 2- --> MgSO4 (aq)
• the more soluble..

  the more it dissolves and so the less precipitate formed
• describe the reaction between strontium and a sulphate ion

  • when a solution contains Sr2+ ions is added to a solution containing SO4 2- ions
  • a colourless solution contains SrSo4 is formed
  • SrSo4 is slightly soluble so forms a small amount of white precipitate in the colourless solution
  • equation : Sr2+ (aq) + So4 2- (aq) --> SrSo4 (aq)