Question

How to learn or some easy way to learn valencies in chemistry for class 7

Answer 1

First u have to learn the atomic number of elements at least 20.Then u try to arrange them in shells.It it he outermost shell has more than 4 electrons,then subtract it from 8.This gives you valence of that element

Answer 2

Yes there is an easy way to find out
the valencies of all atoms. Ok so firstly
you don't need to remember all of
them. Even in college only a few come
in handy. I have a trick which can be
very useful in finding the valencies of
about 75 percent elements in the
periodic table.
Let me take the example of oxygen.
Look at its electronic configuration. It
is 2,6. Now it needs to have 8
electrons in the valence shell
according to the octet rule. If it gets 2
electrons this would satisfy the
condition and make it reach the
electronic configuration of the nearest
noble gas. Thus the valency of oxygen
is -2!!
This works on almost all atoms. You
just need their electronic
configuration which can be easily
found out using their atomic number.
Then find at which point they require
the lowest energy- in gaining or losing
electrons. Remember, always the
lowest energy requiring process is
favoured. And also remember the
octet rule.
Sorry for being late in answering your
question. Hope it helps!!