What is the ground state electron configuration of a ""_27 "Co" atom in the gas phase?

1 Answer
Truong-Son N.
Mar 7, 2016

Cobalt is atomic number 27, which means it has 27 electrons as a neutral atom (protons and electrons cancel out when charge = 0).

If you looked at the periodic table, it's a 3d metal, in the fourth period, so the ground-state electron configuration is:

color(blue)(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^7)

That adds up to 2+2+6+2+6+2+7 = 27. It's not "Cu" or "Cr", so it's not a strange configuration. It's implied that it's in the gas phase so it's not really necessary to state that.

In this configuration, three 3d orbitals are singly occupied.

CHALLENGE: Is cobalt paramagnetic or diamagnetic as an atom? How do you know? What is its closest-in-energy first-excited configuration (it cannot promote into the 4s, and it cannot promote into the 4d in one step)?

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