Question

Elements of group 1 and 17 have same valency.Explain

Answer 1

Let us take one element from group 1 and Group 17 to compare their properties

From group 1: Hydrogen

Number of electrons=1

Nearest noble gas-Helium(Atomic number 2)

From group 2:

Number of electrons=9

Nearest noble gas-Neon(Atomic number 10)

Valency is the number of electrons needed to be gained or loosed in order to reach the nearest noble gas configuration

thus, Hydrogen tries to gain 1 electron to attain helium electron configuration

and becomes hydrogen -1 by gaining an electron.

In case of Florine it also tries to gain 1 electron to attain neon's atomic configuration and becomes fluorine -1.

Thus, Elements in group 1 and group 17 have same valency number but not the same sign always.

Try doing this method for other elements and you will find that group 1 will have +1 and group 17 will have -1....