What is the electron configuration of an element with atomic number 3?

1 Answer
Oct 22, 2016


or (for A level chemistry)

#1s^2#, #2s^1#


A simple way to find the electronic configuration is to fill out orbitals. An atom with atomic number 3 has 3 electrons since it is neutral (neutral atoms have equal atomic and electron numbers). The first orbital can hold a maximum of 2 electrons while the second, third, and fourth can accommodate 8, 16, and 32. (For O levels, just know that all other shells can hold 8. The 16 and 32 arent necessary at that stage).

Since the first shell can only hold two electrons, the first number we write down is 2. Then we move to the next orbital which can hold 8. However, the atom only has one more electron left to place, so only one electron will be on that orbital. We write down 1. Hence. the configuration is 2,1.

Similarly, atoms with atomic numbers 4, 5 and 6 will have electronic configurations of:

Notice that when we add all the numbers in the configuration, we get the total number of electrons in the atom.