Electronic Structure of Atoms

Electron configurations and the periodic table

The periodic table is structured so that elements with the same type of valence electron configuration are arranged in columns.

• The left-most columns include the alkali metals and the alkaline earth metals. In these elements the valence s orbitals are being filled
• On the right hand side, the right-most block of six elements are those in which the valence p orbitals are being filled

• In the middle is a block of ten columns that contain transition metals. These are elements in which d orbitals are being filled
• Below this group are two rows with 14 columns. These are commonly referred to the f-block metals. In these columns the f orbitals are being filled

Important facts to remember:

1. 2, 6, 10 and 14 are the number of electrons that can fill the s, p, d and f subshells (the l=0,1,2,3 azimuthal quantum number)
2. The 1s subshell is the first s subshell, the 2p is the first p subshell (n=2, l=1, 3d is the first d subshell, and the 4f is the first f subshell
   

What is the electron configuration for the element Niobium? (41)

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d³

Niobium is actually:

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s¹ 4d⁴

The reason is that the 5s and 4d energy levels are quite close and certain electronic arrangements can result in the levels being slightly different than expected.

What is the electron configuration of the element Nickel? (28)

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁸

What is the electron configuration for Nickel in terms of the nearest noble gas?

[Ar] 4s² 3d⁸

How would the last valence orbital be filled?