Atoms that have unpaired electrons in their orbitals are said to be paramagnetic. Such substances show weak attraction towards the external magnetic field by a behavior called paramagnetism. On the other hand, substances having all electrons paired, are termed diamagnetic. Such substances experience no attraction (slight repulsion) from the external magnetic field. This behavior is called diamagnetism.
Paramagnetic vs Diamagnetic Substances
|Paramagnetic Substances||Diamagnetic Substances|
|These substances are weakly attracted by the external magnetic field||There is a slight repulsion by the external magnetic field for such substances|
|Paramagnetic substances becomes diamagnetic under high temperature||The temperature has no effect on diamagnetic substances|
|Paramagnetic substances have relative permeability > 1||Diamagnetic substances have relative permeability < 1|
|Their magnetic susceptibility is positive||Their magnetic susceptibility is negative|
|They contain unpaired electrons||They contain paired electrons only|
|Do not show levitation||Show static magnetic levitation|
|Doped semiconductors show paramagnetism||Pure semiconductors show diamagnetism|
|Examples of paramagnetic substances are lithium atom, nitrogen atom, oxygen molecule, etc||Examples of diamagnetic substances are gold, copper, nitrogen gas, water, etc|
Paramagnetic Substances and Paramagnetism
Paramagnetic substances are atoms or molecules having unpaired electron(s). Greater the number of unpaired electrons, the more the paramagnetic behavior there is. When an external magnetic field is applied to a paramagnetic substance, it shows an attraction toward the field. This is due to the parallel spin of electrons in orbitals. Electrons fill the orbitals according to Hund’s rule which states that:
“Electrons prefer to be unpaired and are only paired when all the orbitals of the subshell are half-filled (with parallel spin)”
Paramagnetic substances are attracted (weakly) towards the external magnetic field. This is due to the unpaired electrons that function as microscopic magnets when placed in a magnetic field. The magnetic effect produced by the electronic spin when couples with the external magnetic field, a combined effect is produced. It is observed that only a small fraction of the tiny magnets are aligned in the induced magnetic field due to thermal properties. Therefore, these substances are weakly attracted when placed in a magnetic region.
Examples of Paramagnetic substances are;
- Nickel (Ni)
- Chromium (Cr)
- Titanium (Ti)
- Aluminum (Al)
- Barium (Ba)
- Rubidium (Rb)
- Strontium (Sr)
- Molybdenum (Mo)
- Nitrogen gas (N2)
- Oxygen gas (O2)
- Lithium atoms (Li)
- Iron oxide
- Neodymium (Nd)
- Dysprosium (Dy)
- Terbium (Tb)
- Hafnium (Hf)
- Yttrium (Y)
- Zirconium (Zr)
- Tungsten (W)
- Many metallic complexes, etc
The magnetic behavior of nitrogen gas shown below explains why nitrogen atoms are paramagnetic.
Another example of paramagnetic substances is O2 gas in its molecular form because it has two unpaired electrons in its molecular orbitals as shown in the energy level diagram below.
The two unpaired electrons present in the π* region of the Anti Bonding Molecular Orbital (ABMO) are the reason for the paramagnetic property of the oxygen (O2) molecule.
Diamagnetic Substances and Diamagnetism
Diamagnetism was discovered by Michael Faraday in 1845. They are the weakest magnetic substances with a magnetic susceptibility close to zero. It is the property of atoms and molecules exhibited by the pairing of electrons. Once electrons are in pair, they have an opposite spin to each other in orbitals as explained by Pauli’s exclusion principle.
“No two electrons in the same orbital can have the same values of spin quantum numbers”
The opposite spins (↑↓) cancel the effect of each other and are not affected by any of the external magnetic fields. This state of materials is also termed ‘no flux’ condition.
Diamagnetic substances are weakly repelled by the external magnetic fields as they create an induced magnetic field due to the electronic spin in the opposite direction. The detection of diamagnetic materials is very difficult due to their weak repulsion property. They also act as superconductors because they are not disturbed by the external magnetic fields.
Some examples of diamagnetic substances are:
- Gold (Au)
- Copper (Cu)
- Silver (Ag)
- Bismuth (Bi)
- Lead (Pb)
- Tin (Sn)
- Zinc (Zn)
- Sulfur (S)
- Silicon (Si)
- Selenium (Se)
- Chlorine (Cl)
- Bromine (Br)
- Argon (Ar)
- Krypton (Kr)
- Hydrogen gas (H2)
- Water (H2O)
- Table salt (NaCl)
- Marble (Calcium carbonate)
- Glass (Silica-Quartz)
- Antimony (Sb), etc
The diamagnetic behavior of the zinc atom depicts how the canceled spins of electrons leave the material undetected by the magnetic fields.
Hydrogen gas (H2) is diamagnetic gas in its molecular form because it has paired electrons in its orbitals. The expected molecular orbital energy level (MO) diagram of the hydrogen molecule is given as:
Ferromagnetism and paramegnetism
Ferromagnetic substances are almost similar to paramagnetic substances. Iron (Fe), cobalt (Co), Gadolinium (Gd), and nickel (Ni) are ferromagnetic materials. They are attracted towards applied magnetic fields like paramagnetic ones but in this case, the attraction is millions of times larger than paramagnetic substances. This strong attraction is explained by the presence of domains. Domains are the regions of aligned magnetic fields that exist in ferromagnetic materials. When they are placed in magnetic fields, they align themselves along the direction of external magnetic fields creating a greater net effect.
How to tell if an element is paramagnetic or diamagnetic?
The elements which have unpaired electrons in their orbitals are paramagnetic and are attracted by the magnetic field. Those elements which have paired electrons are diamagnetic and weakly repelled by the external magnetic field.
What are paramagnetic and diamagnetic materials?
Paramagnetic materials are slightly attracted toward the external field due to the fact that they have unpaired electrons in their orbitals. While diamagnetic materials are weakly repelled under the influence of external magnetic fields as they have paired electrons in their orbitals.
Is diamagnetic stronger than paramagnetic?
Diamagnetic substances are stronger than paramagnetic ones because the relative permeability of paramagnetic materials is less than 1 and they have a negative value of magnetic susceptibility. Diamagnetic materials have both positive magnetic susceptibility and relative permeability of more than 1.
Is magnesium diamagnetic or paramagnetic?
Magnesium has no unpaired electrons but still, it is paramagnetic due to altered spinning of electrons under an external magnetic field.
Is Ti2 a paramagnetic or diamagnetic?
Titanium ion has unpaired electrons in orbital which makes it paramagnetic.
Is Ne2 a paramagnetic or diamagnetic?
The expected molecular orbital energy level diagram of a neon molecule has no unpaired electrons so it is diamagnetic if it exists.
Why is bismuth considered diamagnetic?
Bismuth has all electrons paired in their outermost shell so, it acts as diamagnetic material.
- General Chemistry Principles and Structure | Third edition, by James E. Brandy (St. John’s University, Jamaica, New York) and Gerard E. Humiston (Widener University, West Chester, Pennsylvania) – [SI version, Prepared by Henry Heikkinen (University of Maryland, USA)]
- Chemistry | fifth edition, by Steven S. Zumdhal and Susan A. Zumdhal (University of Illinois, Urbana Champaign, IL, USA)
- Magnetic Type of the elements (periodictable.com)