- Created by: ZeddHussain
- Created on: 28-12-16 21:34
What are Alkali Metals?
Alkali Metals are the first group on the left hand side of the periodic table.
This group consists of Lithium, Sodium, Potassium, Rubidium, Caesium and Francium.
You will only see the first 3 in school as Caesium and Rubidium are too reactive to use in schools and Francium is an extremely unstable and highly radioactive element.
Properties of the Alkali Metals
All alkali metals are very reactive, therefore they have to be stored in oil which prevents them froom reacting with the oxygen in the air. Their reactivity increases as you go down in the group.
All alkali metals have very low density compared with other metals, which means they can float and that they are very soft and can be cut with a knife. They have a very shiny, silvery surface when you first cut then, howver this quickly goes dull as the metals react with the oxygen in the air. This forms a layer of oxide on the surface for example:
Sodium + Oxygen = Sodium Oxide
4Na(s) + O2(g) = 2Na2O
In a gas jar of oxygen, hot alkali metals burn vigorously, forming a white smoke of their oxides.
The properties of this unusual group is due to their electronic structure. Alkali metal atoms have only one electron in their outer-most shell. This makes them very reactive since they only need to lose one atom to get the stabe electronic structure of a noble gas. They form a metal ion with a +1 charge. They always form ionic compounds.
Melting Points and Boiling Points
Group 1 metals melt and boil at relatively low temperatures for metals. Going down the group it gets lower and lower. In fact, caesium turns into a liquid at just 29 degrees.
Reaction With Water
When you add lithium, sodium or potassium to water, the metal floats on the water, moving around and fizzing. The fizzing happens because the metal reacts with the water to from a hydrogen gas.
Potassium reacts so vigorously with the water that the hydrogen produced ignites. It burns with a lilac flame, coloured by the potassium ions formed in the reaction. The reaction between an alkali metal and water also produces a metal hydroxide. This is why they are called alkali metals. They hydroxide of the alkali metals are all soluble in water.The solution is colourless with a high pH.
Alkali metals also react vigorously with non-metals such as chlorine gas. They produce metal chlorides, which are white solids.The metal chlorides all dissolve readily in water to form colourless solutions.
The reactions get more and more vigorous and you go down the group. That is because it becomes easier to lose the single electron in the outer shell to form ions with a +1 charge.
They react in a similar way with fluorine, bromine and iodine. All of these ionic compounds of the alkali metals and non-metals are also white and dissolve easily in water. The solutions formed are all colourless.