Group 2 Elements (OCR A Level Chemistry A) : Revision Note

Stewart Hird

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Structure & Ions

  • All elements in Group 2 (also called alkali earth metals) have two electrons in their outermost shell in the s sub-shell (s2 electron configuration)

  • Redox reactions are the most common reaction of the Group 2 elements

  • Each metal atom is oxidised, losing its two valence electrons to form a 2+ ion with a noble gas configuration

Ca → Ca2+ + 2e-

  • The calcium changes from an electron configuration of [Ar]4s2 to [Ar]

  • Another species will gain the two electrons lost

    • This species will therefore be reduced

  • The Group 2 element can be referred to as a reducing agent as it has reduced another species

Relative Reactivity

  • The reactivity of Group 2 elements increases down the group.

    • As the atomic radii increase there is more shielding

    • The nuclear attraction decreases and it is easier to remove outer electrons

    • Cations form more easily

Reactions with water and oxygen

  • The reaction of group 2 metals with oxygen follows the following general equation:

2M (s) + O(g) → 2MO (s)

          Where M is any metal in group 2

  • We can see this is a redox reaction by looking at the changes in oxidation number of the metal, M, and oxygen

    • M = 0 → +2 so the metal has been oxidised

    • O = 0 → -2 so the oxygen has been reduced

  • The reaction of all group 2 metals with water follows the following general equation:

M (s) + 2H2O (l) → M(OH)(s) + H(g)

  • We can again see this is a redox reaction by taking a look at changes in the oxidation number of each element in the reaction

    • M = 0 → +2 so the metal has been oxidised

    • H = +1 → 0 so the hydrogen has been reduced

    • No change in oxidation number for oxygen

  • The solubility of the hydroxides increases down the group

Reactions of Group 2 metals with acid

  • The Group 2 metals will react with dilute acids to form metal salts 

    • For example, they will form metal chlorides if reacted with hydrochloric acid, HCl

  • When metals react with an acid, the by-product of this reaction is hydrogen gas

    • The reaction of the metals with dilute HCl follows the following general equation:

M (s) + 2HCl (aq) → MCl(aq) + H(g)

  • We can again see this is a redox reaction by taking a look at changes in the oxidation number of each element in the reaction

    • M = 0 → +2 so the metal has been oxidised

    • H = +1 → 0 so the hydrogen has been reduced

    • No change in oxidation number of chlorine

  • The reaction of the metals with dilute sulfuric acid, H2SO4, follows the following general equation:

M (s) + H2SO(aq) → MSO(aq) + H(g)

  • When some of Group 2 metals react with sulfuric acid rather than hydrochloric, an insoluble sulfate forms

  • Going down the group, the Group 2 sulfates become less and less soluble

    • Calcium sulfate is sparingly soluble, but strontium sulfate and barium sulfate are insoluble

  • We can think about the increasing reactivity moving down Group 2 in terms of ionisation energies

  • The atoms of Group 2 elements react by losing electrons to form +2 ions

  • The formation of +2 ions from gaseous atoms requires two ionisation energies

M(g) → M+(g) + e-

M+(g) → M2+(g) + e-

  • Both the first and second ionisation energies decrease down the group as

    • The attraction between the nucleus and outer electrons decreases

    • Atomic radius increases, and there is increased shielding

  • Despite other energy changes taking place when Group 2 elements react, the first and second ionisation energies make up most of the energy input

  • Therefore, as the total energy input from ionisation energies to form 2+ ions decreases down the group, the elements become more reactive and stronger reducing agents

Group 2 - Ionisation Energy Group 2 Elements, downloadable AS & A Level Chemistry revision notes

First and second ionisation energies of Group 2 elements

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Stewart Hird

Author: Stewart Hird

Expertise: Chemistry Lead

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Topic Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.

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