The combining capacity of an atom is known as valency. If the atomic no of an element is 11. Then it's electronic configuration will be 2,8,1 Hence it will loose 1 atom complete it's octet. Therefore it's valency is 1. Take an other example, if an element has a atomic no 6, then it's electronic Configuration will be 2, 4 So it needed 4 more atom to complete it's octet, therefore it's valency is 4.
1 5 1
The combining capacity of the element is known as valency. The no. of electrons present in the last shell determines its valency for ex. Oxygen  its atomic no. is 8. Then its configuration will be 2 ,6. soo the valency of the element becomes 8-6 = 2
And hence the valency of the element will be 2..