Why Fe3+ is more stable than Fe2+?

Fe3+ is more stable

You are going to solve this puzzle about why Fe3+ is more stable than Fe2+. Fe2+ and Fe3+ may differ in their oxidation state and physical and chemical properties. They may also differ in their names. Fe2+ is ferrous and Fe3+ is ferric. The compounds of Fe2+ and Fe3+ are ionic in nature.

Reason Why Fe3+ is more stable?

If we imagine the electronic configuration of  Fe2+ and Fe3+, we should observe that Fe3+ is more stable. In the configuration of Fe2+, the 2 electrons are removed from the 4s orbital because the nucleus attracts other prior orbitals with more attraction so it is easy to remove. on the other hand, the half-filled and completely-filled orbitals are more stable than that of partially filled. so in a configuration of Fe3+, there is half filled d orbital and in Fe2+ there is a partially filled d orbital.

Fe2+ (Ferrous):

  • It is pale yellow and turns violet when reacting with water. 
  • Fe2+ shows the paramagnetic property. If it forms a low-spin complex it may be diamagnetic. Paramagnetic property is the property that shows that it has an unpaired electron in its outermost shell.
  • Fe2+ oxidizes to the Fe3+ ion in the presence of KMnO4, and HNO3. In addition to KMnO4, the pink color it decolorizes shows the exact oxidation of Fe2+.
  • Another colored complexes test to distinguish between Fe2+ and Fe3+ is that Fe2+ forms a red-orange color when reacting with amine ligands.

Fe3+ (Ferric):

  • It is yellow-brown when reacting with the water.
  • Fe3+ shows paramagnetic behavior. 
  • Fe3+ gives the read solution when reacting with the thiocyanate ions. This method is used to flake blood in movies and films.
  • The basic difference between Fe2+ and Fe3+ is the number of electrons. 

General configuration of Fe:

Iron is a chemical element with the atomic number 26. Its oxidation states range from -2 to +6. But now here I will illustrate the configuration of Fe2+ and Fe3+. The general configuration of Fe is [Ar] 3d6, 4s2.

Fe3+ is more stable tha Fe2+

Variable Electrovalency:

Some elements show more than one valency is known as variable valency. For example, in ferric sulfate Fe2(SO4)3, the valency of Fe is 3. In ferrous sulfate FeSO4, the valency of Fe is 2. Variable electrovalency depends upon the stability of the core. If all the valence electrons are removed by an atom, the residue obtained is called the core. The core obtained from the normal element is more stable if it has 2 or 8 electrons. The electronic configuration of the sodium atom is:

1s2, 2s2, 2p6, 3s1

When sodium removes its 3s1 electron and attains the electronic configuration of noble gas (neon), the residue obtained is called the core. The remaining residue is stable if it has two or eight electrons or vice versa. The d-block elements show variable valency.

Example Along Period


Fe26 = 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d6

When two electrons are removed from Fe, then we get;

Fe2+ = 1s2, 2s2, 2p6, 3s2, 3p6, 3d6

We remove 4s2 in Fe26 because the fourth shell is completely removed and the nucleus attracts the remaining three shells with greater force. When three electrons are removed from Fe26 than we get;

Fe3+ = 1s2, 2s2, 2p6, 3s2, 3p6, 3d5

This Fe3+ is more balanced than Fe2+ because half-filled and completely filled is more stable than partially-filled.


Co27 = 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d7

When two electrons are removed, then we get;

Co2+ = 1s2, 2s2, 2p6, 3s2, 3p6, 3d7

When three electrons are removed from Co27, then we get;

Co3+ = 1s2, 2s2, 2p6, 3s2, 3p6, 3d6

Co2+ is more stable than Co. When we compare Co2+ and Co3+, both are equally stable but Co3+ is slightly more stable than Co2+.


Ni28 = 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d8

Ni2+ = 1s2, 2s2, 2p6, 3s2, 3p6, 3d8

Ni3+ = 1s2, 2s2, 2p6, 3s2, 3p6, 3d7

Ni2+ is more stable than Ni. Ni2+ is more common and more stable than Ni3+ because it is only two steps away from completion and completes the valence shell.

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