Question

Define valence electron by giving examples of phosphorus and chlorine

Answer 1

valence of an atom is the number of electrons gained ,shared or lose by an atom to acquire stable like nearest noble gas. The number of electrons loses or gained are valance electrons .
Ex.. phosphorus 15 atomic number so it's electronic configuration will 2,8,5 .so it needs 3 electrons to be stable like Argon so its shares three electrons so its valancey is -3.
Chlorine ;
17 atomic number so it's electronic configuration will 2,8,7 so it needs 1 electrons so it shares one electron to be stable so its valence electrons is -1

Answer 2

The outermost electron is called valence electron.

eg :- (1) phosphorus:-
atomic no-> 15
electronic configuration -> 2,8,5
so valence electron = 5

(2) chlorine :-
atomic no=> 17
electronic configuration = 2,8,7
so valence electron= 7

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