Question

explain the rules to write electronic configuration of atoms having electrons more than one.

Answer 1

rules are
example aluminium
its atomic number is 13
rule for electronic configuration is the formula 2,8,8 this formula is applied till atomic number 20
in the first shell there is just 2 electron
in the second shell there is 8 electrons
in the third shell there is also 8 electrons
according to element aluminium its atomic number is 13
so in the first shell there will be 2 electrons
how many electrons are left than for the other two shells are 13-2 =11
in the second shell there will be 8 electrons out of 11 electrons according to the formula
now there will be 11-8 =3
only 3 electrons are left for the third shell
now u know that if less than 4 electrons are left than the atom can only donate the electron as energy to gain 5 more electrons to be stable is more and if there is 4 electrons then the atom can donate or accept according to the reaction and if there is more than 4 electrons than the atom is accept electrons to be stable
therefore in the aluminium case there are 3 electrons left for the third or the outermost shell . 3 is less than 4 so its valency will be +3
positive valency - when atom donates electrons
negative valency- when atom accept electrons
electronic configuration of atom of aluminium will be - 2,8,3
where 2 electrons is in the first shell
8 electrons in the second shell
3 electrond in the last or outermost shell

thankyou ....... hope it helps you...