# What is diamagnetism?

Apr 6, 2016

Diamagnetism is a quantum mechanical effect where the lack of unpaired electrons allows for an induced magnetic field that repels an applied magnetic field. In other words, apply a magnetic field onto a diamagnetic substance and it slightly resists it.

This effect is generally weak, and if a substance is paramagnetic (has unpaired electrons), it usually will render the diamagnetism insignificant.

To determine diamagnetism:

1. Write out the electron configuration.
2. See if for any orbitals, the number of electrons is $1$.
3. If so, the substance is paramagnetic. If not, it is diamagnetic.

$\text{Co}$ has a configuration of $\left[A r\right] 3 {d}^{7} 4 {s}^{2}$. Since there are five $3 d$ orbitals, then according to Hund's rule, three orbitals have unpaired electrons, and two have paired electrons.

($2 + 2 + 1 + 1 + 1 = \setminus m a t h b f \left(7\right)$ electrons in the $3 d$ subshell, as stated from the electron configuration.)

Thus, $\text{Co}$ is paramagnetic.

CHALLENGE: Can you see that $Z n$ is diamagnetic?