Page 149 - Chemistry ICSE Class IX

The Periodic Table 137
(b) The nonmetallic character increases while going from left to right in a
period. In any group, the nonmetallic character decreases while going
from top to bottom, i.e.,

So, the most nonmetallic element should lie at the top of the group on the extreme
right of the periodic table (excluding the group zero). Therefore, the element B is
the most nonmetallic.
(c) The atomic size increases while going from top to bottom in a group and
it decreases while going from left to right in a period, i.e.,

So, the element at the top of the group on the extreme right (excluding noble gases)
will have the smallest atom. Therefore, atom of element B is the smallest.

EXAMPLE 5.4. Given below are the melting points and the atomic radii of three
elements X, Y and Z, each having n electrons in the outermost shell of their atoms:
Element X Y Z

Melting point (°C) 180.5 97.8 63.7
Atomic radius (Å) 1.20 1.31 1.36
Answer the following:
(a) Are the valencies of these elements same or different?
(b) Which element has the highest atomic number?
Solution: As an atom of each element has the same number of electrons in their
valence shell, hence these elements belong to the same group of the periodic table.
So,
(a) All these elements have the same valency.
(b) In a group, the size of the atom increases with atomic number. So, the element
Z has the highest atomic number.

Alkali Metals (Group 1)

Elements of Group 1 (or Group IA) are called alkali metals. Group 1 (or
Group IA) contains Lithium (Li), Sodium (Na), Potassium (K), Rubidium
(Rb), Cesium (Cs) and Francium (Fr). These elements are collectively called
alkali metals.

What are the general characteristics of alkali metals
Some common/general characteristics of alkali metals are described below:
ƒ Occurrence. All alkali metals are highly reactive and therefore, do not
occur in free metallic state. These metals occur as their compounds.
For example,