Group 2, The Alkaline Earth Metals (Oxford AQA International A Level (IAL) Chemistry) : Revision Note

Group 2 Trend: Atomic Radius

• Group 2 are know as the alkaline earth metals

• Going down the group, the elements become larger as the outer two electrons occupy a new principal quantum shell which is further away from the nucleus

Trend in atomic radius down Group 2

Graph to show the trend in atomic radius down Group 2

Group 2 Trend: First Ionisation Energy

• All Group 2 metals can form ionic compounds

  • They donate their two outermost electrons to become an ion with +2 charge

  • Group 2 metals therefore act as reducing agents and are themselves oxidised

• Going down the group, the metals become more reactive

• This can be explained by looking at the Group 2 ionisation energies:

Graph to show the trend in first and second ionisation energy down Group 2

• The first ionisation energy is the energy needed to remove the first outer electron of an atom

• The second ionisation energy is the energy needed to remove the second outer electron of an atom

• The graph above shows that going down the group, it becomes easier to remove the outer two electrons of the metals

• Though the nuclear charge increases going down the group (because there are more protons), factors such as an increased shielding effect and a larger distance between the outermost electrons and nucleus outweigh the attraction of the higher nuclear charge

• As a result of this, the elements become more reactive going down the group as it gets easier for the atoms to lose two electrons and become 2+ ions

• This trend is shown by looking at reactions of the Group 2 metals:

  • With dilute hydrochloric acid:

    • bubbles of hydrogen gas are given off much faster indicating that the reactions become more vigorous

  • With oxygen:

    • the metals get more reactive with oxygen down the group (Ba is so reactive, that it must be stored in oil to prevent it from reacting with oxygen in air)

Group 2 Trend: Melting Point

• Group 2 metals have giant metallic structures so have high melting points

• The melting point of the elements decreases going down the group as the outer electrons get further away from the nucleus

• This means that the attraction between the nucleus and the bonding electrons decreases causing a decrease in melting point

 Graph to show the trend in melting point down Group 2