User:Phaello/sandbox/Chemistry/CHE 1401S-A/Electronic Configuration Part 1

Electronic Configuration of Atoms
Atoms consist of a nucleus that is surrounded by shells. The shells are labelled 1, 2, 3 etc starting from the inner most shell going outwards. The inner most shell is at the lowest energy level, while the outer most shell is at the highest energy level. This means that energy levels increase as you move from the inner most shell outwards.

Each shell has one or more subshells. Each subshell in turn consists of orbitals, which may be taken to be a region/space where an electron is likely to be found. For example, the first shell has one subshell, known as 1s, and this subshell has one orbital; the second shell has 2 subshells, namely 2s and 2p, 2s subshell has one orbital, 2p subshell has 3 orbitals; the third shell has 3 subshells, namely 3s, 3p and 3d, subshell 3s has one orbital, 3p subshell has 3 orbitals, and 3d subshell has 5 orbitals.

An orbital can take a maximum of 2 electrons
First shell has one subshell, with one orbital, hence first shell taking a maximum of 2 electrons.

Second shell has 2 subshells: 2s subshell with one orbital, 2 electrons, 2p subshell with 3 orbitals, each can take 2 electrons (making 6 electrons in 2p subshell) so the shell can take a maximum of 8 electrons.

Third shell has 3 subshells: 3s subshell with one orbital, 2 electrons, 3p subshell with 3 orbitals, each can take 2 electrons (making 6 electrons in 3p subshell), 3d subshell with 5 orbitals, each can take 2 electrons (making 10 electrons in 3d subshell) – the shell therefore can take a maximum of 18 electrons.

The electronic configuration of Hydrogen which has 1 electron will therefore be 1s1.

That of Helium which has 2 electrons is 1s2

That of Lithium which has 3 electrons is 1s2 2s1

CHE 1401S-A					Lecturer: P. Ntšonyane		March 17, 2009