# Introduction

The s- block elements of the periodic table constitutes group -1 and group -2 elements. Group -1 is called alkali metals and group -2 alkaline earth metals. The oxides and hydroxides are alkaline in nature. The general electronic configuration is 1s1 for alkali metals and 1s2 for alkaline earth metals. These elements are highly reactive and form M+ and M++ ions respectively. In this chapter we will be studying the important compounds of sodium that is sodium carbonate. Under the alkaline earth metals we will specially study the preparation of Portland cement. Further we will study the importance of potassium, sodium, magnesium and calcium in our biological systems.

In the block - wise division of the periodic table, the four clearly identified blocks of elements area the s-block, the p-block, the d-block and the f-block.
In the build-up of atoms elements belonging to a particular block receive their outermost electrons  in  s-,p-,d- or f- orbitals. As the s-orbital can accommodate only two electrons, two groups(1 and 2) belong to the s-block of the periodic table. Group 1 consists of the elements: lithium, sodium, potassium, rubidium, cesium and francium. They are collectively known as the alkali-metals. The elements of Group 2 include beryllium magnesium, calcium, strontium, barium and radium. These elements with the exception of beryllium are commonly known as the alkaline earth metals.

Among the alkali metals sodium and potassium are abundant, lithium, rubidium and cesium have much lower abundances. Francium is radioactive: its longest- lived isotope 223Fr has a half-life of only 21 minutes. Of the alkaline earth metals calcium and magnesium rang fifth and sixth in abundance respectively in the earth's crust. Strontium and barium have much lower abundances. Beryllium is rare and radium is the rarest of all comprising only 10-10 per cent of igneous rocks.
A regular trend is observed in the physical and chemical properties of the alkali metals with increasing atomic number. The loosely held s-electron in the outermost valence shell of these elements makes them the most electropositive metals which readily give ions, M+. The relationship between the elements of the alkaline earth metals is similar to that between the alkali metals. Calcium, strontium, barium, with two s-electrons in the valence shell, are also highly electropositive. They form M2+ ions.

Lithium and beryllium, the first elements of Group 1 and Group 2 respectively exhibit some properties that are different from those of the other members of the respective group. In these anomalous properties they resemble the second element of the following group. Thus lithium shows similarities to magnesium, and beryllium to aluminium in many of their properties. This type of diagonal similarity is commonly referred to as diagonal relationship in the periodic table. The diagonal relationship is due to similarity in ionic sizes and/or charge/radius ratios of the elements.