Question

how can the valency of an element can be determined if its electric configuration is known?what will be the valencyof element of atomic mumber9?

Answer 1

the no. of electrons that an atom takes or receive is called valency
if electronic configuration of an element is known suppose atomic number of oxygen is 8 then it's electronic cofiguration will be 2,6, and it need 2 more electrons to complete it's outermost orbit so o2 will take 2 electrons and it's valency become 2.in this way if electronic configuration of element is known we can determine it's valency
if an atoms atomic no. is 9 then it's electronic configuration must be 2,7 so it requires 1 electron to complete the octet so it will take 1 electron and it's valency will be 1

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Answer 2

valency of an element can be determined by its electronic configuration let state one example like sodium that is Na letters write its electronic configuration that is 1s2,2s2,2p6,3s1 here to check the valency we have to count number of valence electrons are there 11 Valence Electrons and there is one electron in outermost shell Na has to get octet configuration like any other element sodium loses its outer shell electron so that it can get octet configuration in its outer shell after losing an electron means we know that 2 orbit is having 8 electrons . so valency is nothing but the number of electrons lost or gained by an element to obtain octet configuration



coming into the second question the element of atomic number 9 will have
valency1s1,2s2,2p5

so here the outermost shell is second Orbit and it has 7 electrons so to obtain octet configuration it has to gain one electron so the valency will be one


actual definition of valency is the combining capacity of an element


but for your convenience I used another definition which should not be written in exam