1Group 1 in water
The alkali metals react with water, fizzing as they give off hydrogen. Going down the group they get more reactive.
alkali metalsreactivity
Lesson 20.4 notes
Patterns in groups
Group 1, Group 7 and Group 0: their reactions, the patterns down each group, and predictions.
2What they make
sodium + water → sodium hydroxide + hydrogen. The hydroxide dissolves, making an alkaline solution.
hydroxide
3Stored under oil
Alkali metals are soft enough to cut with a knife. They react quickly with air and water, so they are kept under oil.
4A pattern down the group
Going down Group 1, melting points decrease and reactivity increases. The pattern lets you predict rubidium and caesium.
5The halogens
The halogens (Group 7) get darker going down: fluorine and chlorine are gases, bromine is a liquid and iodine is a solid.
halogens
6Displacement
A more reactive halogen displaces a less reactive one from its compounds. Halogens get less reactive going down the group.
displacement
7The noble gases
The noble gases (Group 0) are very unreactive. Helium fills balloons, argon is used in filament bulbs and neon glows in signs.
noble gases
Explore: Reactivity lab
Drop a Group 1 metal into water, or add a halogen to a salt solution, and compare the reactions.
Common mistake: Reactivity goes opposite ways in Groups 1 and 7
Going down Group 1 the metals get more reactive: potassium is more reactive than sodium. Going down Group 7 the halogens get less reactive: chlorine is more reactive than bromine.
Remember
- Group 1 metal + water → metal hydroxide + hydrogen. Reactivity increases going down the group.
- Group 7 gets darker and less reactive going down. A more reactive halogen displaces a less reactive one.
- Group 0, the noble gases, are very unreactive.
Going further at GCSE