Alkali Metals - Group 1

 Alkali metals are a different type of metal, these metals are as follows, from top to bottom.

Lithium.

Sodium.

Potassium.

Rubidium.

Caesium.

Francium.

These elements unlike most other metals, have low melting points, are brittle and have very low densities, Caesium, for example, explodes at room temperature and is reactive to Oxygen, and they get more reactive the further you go down the chart, and for another example, lithium which is used in lithium-ion batteries are explosive when in contact with water. 

Along with being more reactive the boiling points and the melting points decrease meaning the further you go down the easier it is to melt or boil the water, the reason why these elements or atoms are so unstable is that they only have one electron in their outer shell,
and since they only have one electron in their outermost shell, another reason why they are extremely reactive is because the single electron is on the outer-most shell which is very far from the central nucleus of their atom.

They often combine with non-metals to form ionic compounds, these happen by the Alkali atom donates its singular electron to another element.
Which in this case will be a Chlorine atom, when the Sodium atom loses its electron it becomes an ion, and since the Chlorine atom gains an electron it becomes negatively charged while the Sodium atom becomes positively charged thus making them both attracted to each other. 

When an Alkali metal comes in contact with water, it forms Metal-Hydroxide and Hydrogen gas, which in chemical terms would be written as:
2Na + 2H20 = 2NaOH + H2.

But from Potassium onwards, the elements get so reactive that they will ignite the hydrogen gas, and we know hydrogen gas is very explosive. 

Na+ Cl = NaCl, or Sodium + Chlorine = Sodium-Chloride, this ionic compound is a common table salt which is used in foods.

When these Alkali metals come in contact with Oxygen, they become metal oxides, for example, if we take Lithium and mix it with oxygen we get Lithium Oxide or Li20, or if we take Sodium and combine it with Oxygen we get Sodium Oxide or Na20, 
Or Potatsium and Oxygen we get Potasssium Peroxide or K2O2, or KO2, which is Potassium superoxide.