Group Properties
Resumen
In a school preparation room there is a jar of soft grey metal sitting under a layer of oil, and the oil is not there to keep it clean. It is there because the metal cannot be left alone with the air, let alone with water. Cut a piece with a knife and the fresh surface is bright for a second or two before it dulls. Drop that piece into a trough and it floats, because it is lighter than the water it is busy attacking. Almost nothing else on the chart behaves like that, and the reason is written into where the metal sits.
This lesson is about one column of the periodic table and what changes as you travel down it. The reaction with water goes from a steady fizz at the top to something no school would attempt at the bottom, and the escalation is completely regular. One sentence about outer electrons explains the whole of it. Along the way you will learn to predict the behaviour of elements too reactive to be handed to you in a bottle, and to turn a table of measurements into a statement an examiner will pay for.
Objetivos
- The elements in Group 1 of the periodic table (known as the alkali metals): are metals with low density (the first three elements in the group are less dense than water); react with non-metals to form ionic compounds in which the metal ion carries a charge of +1. The compounds are white solids that dissolve in water to form colourless solutions; react with water, releasing hydrogen; form hydroxides that dissolve in water to give alkaline solutions.
- In Group 1, the further down the group an element is, the more reactive the element.
- The trends in reactivity within groups in the periodic table can be explained because the higher the energy level of the outer electrons: the more easily electrons are lost Students should be able to explain the relative reactivities of the elements in Group 1.
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Nota de la lección
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- Which statement about the elements of Group 1 is correct? A. They form ions with a charge of -1. B. They become less reactive going down the group. C. They react with water to release hydrogen. D. Their compounds are coloured solids. Answer: C
- Lithium, sodium and potassium all float when added to water. This is because they: A. have a density less than that of water B. have low melting points C. are held up by the hydrogen produced D. do not dissolve in water Answer: A
- Sodium is added to water containing universal indicator. Which pair of products is formed? A. Sodium oxide and hydrogen B. Sodium hydroxide and oxygen C. Sodium hydroxide and hydrogen D. Sodium hydride and oxygen Answer: C
- A piece of rubidium is added to cold water. Compared with potassium, the reaction is expected to be: A. slower, because rubidium atoms are heavier B. slower, because rubidium has more electron shielding C. more vigorous, because the outer electron is lost more easily D. identical, because both metals are in Group 1 Answer: C
- Why is potassium more reactive than sodium? A. A potassium atom has more outer electrons than a sodium atom. B. A potassium atom has a lower density than a sodium atom. C. The outer electron of potassium is in a higher energy level and is lost more easily. D. A potassium atom gains an electron more easily than a sodium atom. Answer: C
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