In this chapter we will discuss about 'Group 1 elements Alkali metals : Alkali metals are Lithium Li; Sodium Na; Potassium K; Rubidium Rb; Caesium Cs and Francium Fr. Sometimes hydrogen is also included in the group. Except hydrogen all other elements of the group are referred as alkali metals because their oxides form strong alkalies when dissolved in water.In the previous concept we studied Alkali metals- introduction, In this concept we study about Occurrence and General Characteristics of Alkali metals and Characteristics.I All the alkali metals are silvery white except Caesium, which is golden yellow solids. Silvery lustre is due to highly mobile electrons of the metallic lattice.Group 1 A atoms are the largest in their horizontal periods in the periodic table. When the outermost electron is removed to give a positive ion, the size decreases considerably. There are two reasons for this:
i. The positive charge on the nucleus is now acting on lesser number of electrons, i.e., attraction increases which brings contraction in size.Atomic as well as ionic size increases from Lithium to Francium due to the presence of one extra shell of electrons.
ii. Softness also increases from Li to Cs due to weaking of interatiomic attractions.
iii. All are soft metals and can be cut with knife. When freshly cut, they have bright lustre which quickly tarnishes due to surface oxidation.
Iv. At normal temperature, all the alkali metals adopt body centered cubic bcc type of lattice with a co-ordination number of 8.
v. At higher temperature above 156 KLi metal crystallizes as BCC crystal, like other alkali metals and on cooling below 72 K it begins to transform in FCC structure. At very high temperature, Lithium forms a hexagonal close packed structure with co-ordination number 12.

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