Chemical Families
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
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Guidelines and tips
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Community
Ask the community
Ask the community for help and clear up your study doubts
University Rankings
Discover the best universities in your country according to Docsity users
Free resources
Our save-the-student-ebooks!
Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors
Trend in Group 7 reactivity. A more reactive halogen can displace a less reactive halogen from a solution of its halide salt. displaces chlorine.
Typology: Study notes
2021/2022
1 / 19
This page cannot be seen from the preview
Don't miss anything!
Related documents
Partial preview of the text
Download Chemical Families and more Study notes Chemical Principles in PDF only on Docsity!
Chemical Families
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
Group 1
The Alkali Metals
Lithium Sodium Potassium Rubidium Caesium Li
Group 7
The Halogens
Na K Rb Cs Fluorine Chlorine Bromine Iodine Astatine
F
Cl Br I At
- Group 1 metals are soft – can be cut with a knife
- They become dull soon after being cut, as they react with oxygen in the air rapidly to form alkali metal oxides
- They have low density – lithium, sodium and potassium float on water
- They have low melting points – sodium and potassium melt from the heat generated when reacting with water
û
ü
ü
û
ü ü
û
(only when freshly cut)
They also show trends in their physical properties: Going down Group 1 the metals:
- get more soft
- get more dense
- melting at a lower temperature Based on observing the physical properties of lithium, sodium and potassium, we should be able to predict the physical properties of rubidium and caesium:
- very soft
- more dense than potassium, may not float on water
- easily melted (caesium melts just above room temp.)
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.
e.g. Na
(s)
+ H
2
O
(l)
à NaOH
(aq)
+ H
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.
Group 7 - The Halogens
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
Group 7 – Physical Properties
Going down the group:
- Fluorine is a very pale yellow gas
- Chlorine is a pale green gas
- Bromine is a red-orange liquid, producing an orange vapour readily
- Iodine is a grey solid, producing a purple vapour when warmed Hands up everyone with a coloured vapour What would you predict the physical properties of Astatine to be? What trends is physical properties are described here?
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.
sodium + chlorine → 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.
hydrogen + chlorine à hydrogen chloride
Re-write this word equation as a balanced chemical equation Start this movie at about 46s in.
Reacting chlorine with:
- potassium chloride solution
- potassium bromide solution
- potassium iodide solution What will we see? Why? Reacting bromine with:
- potassium chloride solution
- potassium bromide solution
- potassium iodide solution What will we see? Why?
chlorine + bromide ions à bromine + chloride ions **Cl 2(aq)
- 2Br**
- (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)
+ 2I
- (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.