Paramagnetism and Diamagnetism

Core concepts

In this topic, you will learn about the key differences between paramagnetism and diamagnetism along with some examples.

Topics Covered in Other Articles

• Electronic configuration
• Aufbau Principle
• Quantum number and orbital shapes
• Understanding the periodic table
• Bose-Einstein Condensate

Electron magnetic dipole moment

Magnetism is a physical property involving the motion of the electrically-charged electrons around the nucleus. On a larger scale, this movement of electrons results in the current flowing through an electrified circular wire, producing a magnetic field. Each electron has an spin property defined by the spin quantum number (m_s), which is either +½ or -½. The combination of orbital motion and spin of the electron generates an electron magnetic dipole moment (magnetic momentum), which determines the magnetic field’s the strength and orientation.

Paramagnetism

The atom or a molecule consisting of one or more unpaired electrons shows the paramagnetic property. Paramagnetism is a type of magnetism that involves the weak attraction of a substance toward an external magnetic field. Each atomic orbital is capable of accommodating two electrons and the filling of these electrons follows Hund’s rule. According to Hund’s rule, the electrons occupy all the atomic orbital singly before being paired. These unpaired electrons are capable of spinning in any direction to produce net magnetic dipole momentum. Here, individual unpaired electrons act as tiny magnets.

Initially, in paramagnetic materials, the orientation of magnetic dipole momentum is random. However, after the application of an external magnetic field, magnetic dipoles align in one direction and generate internal induced magnetic fields. The direction of the induced field is the same as that of the applied field.

Example

The electron configuration of Iron( Fe) is given by: [Ar] 3d⁶ 4s₂

Here it observed that Iron along with its ferrous (II) and ferric (III) forms are paramagnetic due to the presence of unpaired electrons.The number of unpaired electrons determine the magnetic momentum, and thus the magnetic strength, which is why Fe³⁺ is more paramagnetic than Fe⁺² due to the presence of an additional unpaired electron.

Diamagnetism

Similarly, diamagnetism is a property of an atom or a molecule having paired electrons. It is a weak repulsion of a substance towards a magnetic field. Pauli‘s Exclusion Principle states that no two electrons can have the same four electronic quantum numbers. The difference in quantum state is due to the orientation of electron spin. In an orbital, if one of the paired electrons has m_s =+ ½  then the other will have  m_s= – ½ spin. For paired electrons, the spins in opposite directions cancel out each other, and hence there is no net permanent magnetic momentum.

The introduction of the magnetic field to diamagnetic material causes a change in the orbital motion of electrons which creates a dipole opposite to the direction of the applied magnetic field.

Example

Electronic configuration of Zinc (Zn): [Ar] 3d¹⁰ 4s²

Here both Zn and Zn²⁺ are diamagnetic due to the absence of unpaired electrons.

Paramagnetism and Diamagnetism Practice Problems

Problem 1

Does O₂ show paramagnetism or diamagnetism?

Problem 2

Does C₂ have paramagnetism or diamagnetism?

Problem 3

What is the difference between paramagnetism and diamagnetism?

Paramagnetism and Diamagnetism Practice Problem Solutions

1: When the 2s and 2p atomic orbitals of oxygen atoms combine to form molecular orbitals, the electrons from 2p orbitals are split into one σ (bonding) and two π (bonding and antibonding) orbitals. The π antibonding orbital contains two unpaired electrons, due to which oxygen molecules show paramagnetic properties.

2: The molecular orbital electronic configuration of C₂ (12 electrons) = σ(1s)² σ∗(1s)² σ(2s)² σ∗(2s)² π(2px)² π(2py)². Since all the electrons are paired, C₂ is paramagnetic.

3: