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Trend in Group 7 reactivity. A more reactive halogen can displace a less reactive halogen from a solution of its halide salt. displaces chlorine.
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Elements in the same Group have the same number of outer shell electrons. The same number of outer shell electrons means similar chemical properties – so each Group is a chemical family. Group 0 – The Noble Gases
Lithium Sodium Potassium Rubidium Caesium Li
Na K Rb Cs Fluorine Chlorine Bromine Iodine Astatine
Cl Br I At
(only when freshly cut)
They also show trends in their physical properties: Going down Group 1 the metals:
Reaction with water Group 1 metals all react with water to produce alkaline solutions of metal hydroxides (this is why they are called alkali metals). They all fizz, producing hydrogen gas. For these reasons we can consider Group 1 a chemical family. Li, Na and K float and move around on the surface of the water while reacting, until they are completely dissolved. It is an exothermic reaction – enough to melt sodium or potassium! Observing the rate of this reaction allows us to compare their reactivity.
(s)
2
(l)
(aq)
2(g) sodium + water → sodium hydroxide + hydrogen Balance this chemical equation.
more reactive Trends in their chemical properties: We find that sodium is more reactive than lithium, and potassium is more reactive than sodium. We can make predictions about the reactivity of rubidium and caesium: their reactions with water will be extremely violent.
The Halogens are the elements in Group 7 They are non-metals, having coloured vapours. The halogens consist of molecules made up of pairs of atoms e.g. chlorine is Cl 2(g) They also show trends in their physical and chemical properties, because they are a chemical family. Cl F
Going down the group:
Group 1 metals react with Group 7 non-metals to make salts called metal halides. For example, sodium metal react with chlorine gas to make sodium chloride.
Re-write this word equation as a balanced chemical equation:
Halogens can also react with other non-metals, sharing their outer shell electrons to form covalent bonds.
Re-write this word equation as a balanced chemical equation Start this movie at about 46s in.
Reacting chlorine with:
chlorine + bromide ions à bromine + chloride ions **Cl 2(aq)
- (aq) à Br 2(aq) + 2Cl - (aq) The solution turns orange as bromine is formed, because chlorine displaces bromine. This shows chlorine is more reactive than bromine. bromine + iodide ions à iodine + bromide ions Br 2(aq)
- (aq) à I 2(aq) + 2Br - (aq) A dark red-brown colouration is seen as iodine is formed, because bromine displaces iodine. This shows bromine is more reactive than iodine. The halogen atoms gain an electron each from the halide ions ( reduction ). The halide ions lose an electron each to become a halogen ( oxidation ). This is a redox reaction
Separate Sciences Explaining the order of reactivity in Group 7 [2,7] [2,8,7] [2,8,18,7] increasing reactivity The nearer the positively charged nucleus the outer shell is, the easier it is for the nucleus to attract an electron from another atom, so the more reactive the element is. Group 7 elements react by attracting an electron to complete their outer shell.