Inorganic Chemistry
8 marks · NormalRead each question and give concise answers about an unobserved alkali metal and explanations for group reactivity.
Francium is an alkali metal that has not been observed directly. Predict two physical properties and one likely reaction with water of francium, based on trends in Group 1.
Explain in terms of electronic configuration why francium is expected to be more reactive than potassium.
The reactivity of halogens decreases down the group. Explain why, in terms of electronic configuration, chlorine reacts more readily than iodine.
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(a) Francium is predicted to be very soft, have a melting point near room temperature, and to react very violently with water to produce francium hydroxide and hydrogen gas. · must show very soft, melting point near room temperature, very violent reaction with water producing FrOH and H2
(b) Francium has more electron shells than potassium, so its outer electron is further from the nucleus and less strongly attracted. This makes it easier to lose the outer electron, increasing reactivity compared to potassium. · must show more shells than potassium, outer electron further from nucleus, less strongly attracted, more easily lost
(c) Chlorine has fewer electron shells than iodine, so when it gains an electron, the added electron is closer to the nucleus and more strongly attracted. In iodine, the added electron is further from the nucleus so the attraction is weaker, making chlorine more reactive than iodine. · must show chlorine has fewer shells than iodine, incoming electron is closer to the nucleus in chlorine, stronger attraction, easier to form 1– ion
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Marking points
B1 (a) · 1 mark · Predicts francium is very soft.
B2 (a) · 1 mark · Predicts melting point near room temperature (21–27°C or similar).
B3 (a) · 1 mark · Predicts francium reacts very violently with water to give FrOH + H2.
B4 (b) · 1 mark · States francium has more shells than potassium/outer electron further from nucleus.
B5 (b) · 1 mark · Relates increased distance/less attraction to increased ease of losing electron (thus greater reactivity).
B6 (c) · 1 mark · States chlorine's new electron added to a shell closer to nucleus than in iodine.
B7 (c) · 1 mark · Explains that the attraction from the nucleus is stronger in chlorine than in iodine.
B8 (c) · 1 mark · Reactivity is greater for chlorine because it forms a 1– ion more readily (stronger attraction for an extra electron).
Worked solution
a) Francium is very soft and is predicted to have a melting point close to room temperature (about 22°C). It will react extremely violently with water to produce francium hydroxide (FrOH) and hydrogen gas.
b) Francium has more electron shells than potassium. Its outer electron is further from the nucleus and feels less attraction, so it is lost more easily, making francium more reactive than potassium.
c) Chlorine has fewer electron shells than iodine. The new electron gained in a reaction is added closer to the nucleus in chlorine, so it is more strongly attracted, allowing chlorine to react more easily than iodine and form a 1– ion.