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Summary Unit 3.2.2 - Group 2, and Group 7 elements NOTES
A-level AQA Chemistry Group 2 and Group 7 elements notes New spec Applicable to most exam boards
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Unit 2Topic 2: Group 2 elements and Group 7 elements
The Group II metals lose two electrons to form 2+ ionswhen they react in order to achieve a
full outer shell.
Atomic Radius
The atomic radius of group II metals increasesdown the group due to additional electron
shells.
Reactivity
Increased electron shielding down the group makes the outer electrons easier to lose.
Therefore reactivity of the group II metals increasesdown the group.
Ionisation Energy
The first ionisation energy of group II metals decreasesdown the group due to a greater
atomic radius and increased amounts of shielding.
Melting Point
The group II elements are metallicmeaning the larger the ions within the metallic structure,
the weaker the attractive forces as the attractive force has to act over a much greater
distance. Therefore the melting points decreasedown the group.
Reactions with Water
The group II metals react with water in a redox reaction to produce a metal hydroxide and
hydrogen. The metal hydroxide form as an alkaline solution, hence why the group II metals
are known as the alkali metals.
Magnesium reacts very slowly in this way with liquid water, however the reaction can be
much faster with steamas it provides the reaction with extra energy. When steam is used,
the magnesium burns with a bright white flameto form hydrogen and magnesium oxide, a
white powder.
, Solubility of Hydroxides
The solubility of group II hydroxides varies and means these compounds have different uses.
Solubility increases down the groupmeaning magnesium hydroxide (Mg(OH)2)is the least
soluble and barium hydroxide (Ba(OH)2)the most soluble.
As a result, magnesium hydroxide is used in medicine as an antacidas it is alkaline and can
neutralise acids. It is used in a similar way in agriculture to neutralise acidic soils.
Solubility of Sulfates
Group II sulfates decrease in solubility down the groupmeaning magnesium sulfate (MgSO4)
is the most soluble and barium sulfate (BaSO4)is the least soluble.
The insolubility of barium sulfatemeans it is very useful in medicine as barium meals. These
are a form of medical tracer that allow internal tissues and organs to be imaged. Barium
sulfate is toxic if it enters the bloodstream, however because it is insoluble, it cannot be
absorbedinto the blood. Therefore it is safe to use in this way.
Barium chloride is used as a test for sulfate ionsas it reacts to form barium sulfate which
forms as a white precipitatewhen sulfate ions are present.
Metal Extraction
Magnesium is used in the extraction of titaniumfrom titanium chloride via a displacement
reaction.
Flue Gas Removal
Calcium oxidereacts with sulfur dioxide to remove it from factory pollutants and prevent it
from being released into the atmosphere. This forms calcium sulfite and water.
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