Chemistry Class 9th
THE s-BLOCK ELEMENTS
291
UNIT 10
THE s -BLOCK ELEMENTS
The first element of alkali and alkaline earth metals differs in many respects from the other members of the group After studying this unit, you will be able to
• describe the general characteristics of the alkali metals and their compounds;
• explain the general characteristics of the alkaline earth metals and their compounds;
• describe
the manufacture, properties and uses of industrially important sodium and calcium compounds including Portland cement; the biological significance of sodium, potassium, magnesium and calcium.
• appreciate
The s-block elements of the Periodic Table are those in which the last electron enters the outermost s-orbital. As the s-orbital can accommodate only two electrons, two groups (1 & 2) belong to the s-block of the Periodic Table. Group 1 of the Periodic Table consists of the elements: lithium, sodium, potassium, rubidium, caesium and francium. They are collectively known as the alkali metals. These are so called because they form hydroxides on reaction with water which are strongly alkaline in nature. 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. These are so called because their oxides and hydroxides are alkaline in nature and these metal oxides are found in the earth’s crust*. Among the alkali metals sodium and potassium are abundant and lithium, rubidium and caesium have much lower abundances (Table 10.1). Francium is highly 223 radioactive; its longest-lived isotope Fr has a half-life of only 21 minutes. Of the alkaline earth metals calcium and magnesium rank 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 –10 rarest of all comprising only 10 per cent of igneous rocks† (Table 10.2, page 299). The
291
UNIT 10
THE s -BLOCK ELEMENTS
The first element of alkali and alkaline earth metals differs in many respects from the other members of the group After studying this unit, you will be able to
• describe the general characteristics of the alkali metals and their compounds;
• explain the general characteristics of the alkaline earth metals and their compounds;
• describe
the manufacture, properties and uses of industrially important sodium and calcium compounds including Portland cement; the biological significance of sodium, potassium, magnesium and calcium.
• appreciate
The s-block elements of the Periodic Table are those in which the last electron enters the outermost s-orbital. As the s-orbital can accommodate only two electrons, two groups (1 & 2) belong to the s-block of the Periodic Table. Group 1 of the Periodic Table consists of the elements: lithium, sodium, potassium, rubidium, caesium and francium. They are collectively known as the alkali metals. These are so called because they form hydroxides on reaction with water which are strongly alkaline in nature. 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. These are so called because their oxides and hydroxides are alkaline in nature and these metal oxides are found in the earth’s crust*. Among the alkali metals sodium and potassium are abundant and lithium, rubidium and caesium have much lower abundances (Table 10.1). Francium is highly 223 radioactive; its longest-lived isotope Fr has a half-life of only 21 minutes. Of the alkaline earth metals calcium and magnesium rank 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 –10 rarest of all comprising only 10 per cent of igneous rocks† (Table 10.2, page 299). The