What are alkali metals on the periodic table?

• Alkali metals are all the elements present in the first group of the periodic table.
• Alkali metals in order from top to bottom are Hydrogen (H), Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs) and Francium (Fr).

Chemical properties of alkali metals:

• Alkali metals are electropositive in nature. This means that the atoms of these elements tend to lose their valence electrons and form positively charged ions.
• Alkali metals donate one electron to form positive ions during chemical reactions or in their solutions

• Alkali metals form ionic compounds with non metals
• Alkali metals combine with halogens or group 7 non metals to form strong ionic salts. For example Lithium Fluoride (LiF), Sodium Chlordine (NaCl), Potassium Chloride(KCl), potassium iodide (KI), etc.
• Alkali metals when dissolved in water react to form their respective metal alkalis and liberate hydrogen. For example when sodium metal is dissolved in water it forms sodium hydroxide, a powerful alkali: 2Na + 2H2O -> 2NaOH + H2

Physical properties of alkali metals:

• Alkali metals have low melting and boiling points
• Alkali metals are malleable, ductile and can be cut with the help of a knife
• Alkali metals are lustrous, but their lustrous surface gets oxidized quickly on exposure to the atmosphere and so they appear as dull, white colored metals after a few seconds of cutting them.

Why do alkali metals include hydrogen, even though hydrogen is a nonmetal?

The elements are arranged in the periodic table in increasing order of their atomic numbers, and so atomic number forms the basis of arrangement of elements in the periodic table. Since atomic number of an element relates closely to its valency, electronegativity and chemical properties, the arrangement of elements in the periodic table is affected by their valency, elect negativity and chemical properties as well, although not based on it. Hydrogen although being a non metallic gas by physical nature, has a valency of +1, that is, it’s atoms have only one electron in their outermost shells, which it loses during chemical reactions to form positively charged ions. This is the case with all the alkali metals in the periodic table and no other element except the alkali metals including hydrogen show this characteristic in the periodic table. Due to this property hydrogen atoms behave like metal atoms in chemical reactions with other non metals, similar to the nature of alkali metals. Thus it is appropriate to place hydrogen in the alkali metals of the periodic table.

Placing hydrogen with helium would break the rule of having elements of similar chemical properties and valencies in one group of the periodic table.