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Summary Inorganic Chemistry Unit 4 Chemistry Pearson Edexcel
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THE ELEMENTS OF GROUPS 1 AND 2Trend in ionization energy and reactivity down the group 2:
• Each element down the group will have an extra electron shell compared to the one above.
This extra inner shells shield the outer electrons front the attraction of the nucleus. Also, this
will mean the outer electrons are further away from the nucleus, which greatly reduces the
electrostatic attraction between the nucleus and the outer electrons.
• Both of these factors make it easier to remove an electron and therefore the first ionization
energy decreases down the group 2.
• This explains the trend in reactivity as it increases down the group as they react by losing
and electron, therefore is it requires less energy to lose it, it will be more reactive.
Group 2 reaction with Water, Oxygen and Chlorine:
• When group 2 elements react they will become a 2+ ion, due to them containing 2 electrons
in their outer shell, and so they lose both of the electrons when they react.
• They react with water to form hydroxides and hydrogen:
• They burn in oxygen to form oxides:
• They react with chlorine to form chlorides:
Reactions of group 2 Oxides and Hydroxides with Water and Dilute Acid:
Solubility of Group 2 Hydroxides and Sulphates:
• As you go down the group, hydroxides become more
soluble.
• As you go down the group 2 sulphates solubility decreases,
until the point where barium sulphate is insoluble.
, Trends in thermal stability of the nitrates and carbonates of the elements in in Group 1 & 2:
• Thermal decomposition is when a substance breaks down due to heat. The more thermally
stable a substance is, the more heat it will take to break it down.
• Thermal stability increases down a group:
o The carbonate and nitrate ions are large negative ions (anions) and can be made
unstable by the presence of a positively charged ion (cation). The cation polarizes
the anion, distorting it. The greater the distortion, the less stable the compound.
o Large cations cause less distortion than small cations as they have a smaller charge
density. The charge is spread over a larger area. So the furter down the group, the
larger the cations, the lower the charge density so the less distortion caused and
therefore more stable compound.
o The greater the charge on the cation, the greater the distortion and the less stable
the carbonate/nitrate compound becomes. Group 2 cations have a +2 charge,
compared to a +1 charge for group 1 cations.
o Therefore group 2 carbonates and nitrates are less stable than those of group 2.
Flame Tests:
• How to perform them:
o Mix a small amount of the compound you’re testing with a few drops of hydrochloric
acid.
o Heat a piece of platinum or nichrome wire in a hot Bunsen flame to clean it.
o Dip the wire into the compound/acid mixture. Hold it in the hot flame and note the
color produced.
• Colors:
o Lithium à Red
o Sodium à Orange/yellow
o Potassium à lilac
o Rubidium à Red-violet
o Caesium à Blue
o Calcium à Brick-red
o Strontium à Crimson
o Barium à Green
• How do the colours appear:
o The energy absorbed from the flame causes the electrons to move to a higher
energy levels. As they go back down they release energy in the form of light . The
difference in energy levels between the higher and the lower determines the
wavelength, which will determine the color of the flame.
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