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Alkali metals. INTRODUCTION

The elements of group 1A, except hydrogen, are called alkali metals. Although hydrogen is in group 1A, it shows nonmetallic properties.

The other members of the group, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr), show common metallic properties. Their electron configurations end with ns1 and their atomic numbers are bigger than those of noble gases by 1. In other words, each period starts with an alkali metal, or each noble gas is followed by an alkali metal.

By giving their valence electron easily in chemical reactions, they form 4-1 charged ions. Because the alkali metals are the elements which have the least ionization energy and the highest atomic radius, in each period they are a group of most active metals. Since the activity of metal increases from top to bottom, francium, Fr, is expected to be the most active metal in the periodic table. In reality, the element cesium, Cs, is the most active metal because francium is a radioactive element (has been isolated only in minute quantities) and its properties have not been determined at all. Some properties of alkali metals are given in the table below.

The melting points, boiling points and densities of alkali metals are lower than those of other metals. The densities of lithium, sodium and potassium are lower than water. As the atomic number of alkali metals increases, their melting and boiling points and their densities decrease. They are rather soft (even lithium, the hardest metal in the group) and can easily be cut with a kitchen knife. Their newly cut surfaces are silvery grey. They are good conductors of heat and electricity.

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