Summarise the rules for writing distribution of electrons in various shells for the first eighteen elements.
The distribution of electrons in various shells of an atom is called electronic configuration. In order to write the electronic configuration of an element, one should proceed as follows:
(i) With the help of atomic number of the element, find out the total number of electrons present in atom.
(ii) All of these electrons in the various shells one by one in the order of increasing energy according to \(2n^2 \) rule.
The maximum number of electrons revolving around the nucleus of an atom in different shells is given by the formula \(2n^2 \)
Maximum number of electrons in shell number 1 = \(2n^2 \) = \(2(1)^2 \) = 2
Maximum number of electrons in shell number 2 = \(2n^2 \) = \(2(2)^2 \) = 8
Maximum number of electrons in shell number 2 = \(2n^2 \) = \(2(3)^2 \) = 18
(iii) The shell having least energy should be filled first and then the other shells of increasing energies are filled.
(iv) Write the name and number of electrons in various shells, starting with the lowest. Each number of electrons is separated from the other shell by a comma. For example, sodium (atomic number 11) has 11 electrons in its atom. According to \(2n^2 \) rule, K shell should be filled with 2 electrons and then L shell will be filled with 8 electrons and in the end one left electron will go to N shell.
Electronic configuration of Na will be K 2, L= 8, M = 1.