The elements in Group I of the periodic table are called alkali metals. They are called alkali metals because they react with water to form alkali solutions. These metals are very reactive; hence they have to be stored under oil to protect them from corrosion by air and water.
Alkali metals are soft and can be cut easily with a razor blade. When freshly cut, the alkali metals show a shiny and silvery white surface that quickly tarnishes in the air. These elements have low densities that generally increase down the Group. They have low melting points that decrease down the Group.
Chemical properties of Alkali metals
Each of the atom of an alkali metal has one valence electron. The atom loses one valence electron to attain stable noble gas electronic configuration. Going down the Group, reactivity of these alkali metals increases. As we go down the Group, the size of atoms increases. There are more electrons in the inner shells, hence, the attraction between positive nucleus and valence electrons decreases. It is easier to lose the outermost electron from bigger atoms. Hence, reactivity increases down the Group.
Reaction of Alkali metals with water
Group I elements react with water to form alkali solutions. When lithium is placed in the water, it reacts quickly. Sodium, which is a more reactive metal, reacts violently, catches fire, and sometimes explode. Potassium reacts very violently, sometimes explosively. Elements that are lower in the Group, they are so reactive, it is not safe to carry out the experiment in the school Chemistry lab.
The alkali formed, contains hydroxide ions, which turn red litmus paper blue.
Formation of ionic compound
Alkali metals form ionic compound with non-metals. Each of the atom of an alkali metal has one valence electron. The atom loses one valence electron to attain stable noble gas electronic configuration. Hence, they form ions with a charge of +1.
The compounds that alkali metals form are all ionic. They have similar chemical formula.
Refer to this video to check out how to work out the chemical formula of Group I ionic compounds.
Topic: The Periodic Table, O Level Chemistry, Singapore
If you would like to know more about the basics of Periodic Table, check out this post.
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