- Describe lithium, sodium and potassium in Group I as a collection of relatively soft metals showing a trend in melting point and reaction with water.
The metals in group I are called alkali metals. They are very soft.
Down group I, the melting and boiling points decrease.
When alkali metals react with water, they produce a metal salt and hydrogen as we know from the general formula that
metal + water ———> salt + hydrogen
But the reactions themselves are not exactly the same.
As you can see, the alkali metals become more reactive down the group.
- Predict the properties of other elements in Group I, given data where appropriate.
The element after Potassium is Rubidium and you can predict that its reaction with water will be much more violent- it will fizz violently, producing plenty of bubbles, move around the surface of the water rapidly and disappear, bursting into flames. We can also predict that Rubidium will have a lower melting and boiling point than the three elements above it. And the elements below Rubidium will be even more reactive and have very low melting and boiling points.
- Describe the trends in properties of chlorine, bromine and iodine in Group VII, including colour, physical state and reactions with other halide ions.
The group VII elements are called halogens. They are poisonous non-metals that have low melting and boiling points that increase down the group. As a result of this increasing boiling and melting points, the state of the halogens at room temperature, changes from gas to liquid to solid down the group (fluorine and chlorine, the first and second halogens, are a gas; bromine, the third halogen is a liquid; and iodine, the fourth halogen, is a solid). The colours of halogens also get darker down the group.
Metal + Halogen ———–> metal salt (halide)
Example: Sodium + Chlorine ———-> Sodium chloride
The salts that halogens form when they react with metals are called halides (chloride, bromide, iodide for example)
When a halogen reacts with a halide, the more reactive halogen will ‘displace’ (more about displacement reactions here) the less reactive halogen.
Example:
chlorine + potassium bromide ———–> potassium chloride + bromine
(here, chlorine is more reactive than bromine so chlorine will replace the bromine in potassium bromide to form potassium chloride)
So, fluorine will displace all the other halides, since it is the most reactive of them. Chlorine will displace all halides except fluoride. Bromine will displace all halides except fluoride and chloride, and so on.
- Predict the properties of other elements in Group VII, given data where appropriate.
Now you can predict how the halogens will be up and down the group. Astatine, the fifth halogen, will have high melting and boiling points so will be solid at room temperature, and will have a very dark colour.
Notes submitted by Lintha
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