Reasons for variable valency

The valency of the same element may change depending on the circumstances of a chemical reaction. Because of this, metals like lead and tin have different valencies. In most circumstances, metals give electrons to produce positively charged ions. But some metals lose electrons from the next to the valence shell. This element has many electropositive valencies. Variable valency describes such elements, and mercury’s valency ranges from +1 to +2.

Reasons for Variable Valency

Some elements have Variable Valency due to electronic configurations. It occurs when electrons change shells.

• The cause for extra electron loss is specific electrons.
• Vacant orbits in the same sub-shells cause electrons to jump between shells.

Variable valency example

• Copper has the atomic number 29. Its electronic configuration is 2, 8, 18 (the second last orbit), and 1 (Valence).
• The second orbit and valence each have one electron.
• As a result of this, the electron will move from one shell to another to become stable.
• The penultimate shell’s outer shell and the last orbit’s outer shell have different valencies.
• In the penultimate shell, copper has a valency of 1, while in the last shell, copper has a valency of 2.
• Ions may have variable valency. For example, Fe+ 2 oxides.

Why do Elements have variable valency?

Consider this iron example:

Iron (Fe) and the atomic number of iron is 26.

Iron electronic configuration = 1s2 2s2 2p6 3s2 3p6 4s2 3d6

3d6 is an unstable molecule because of its electronic arrangement and will eliminate the 4s orbital two electrons first. In this case, the iron’s electronic arrangement is 4s0 3d6, and the electronic configuration 3d6 is unstable.

After losing one electron, the d subshell is half-filled. This 3d5 electronic arrangement is stable. Iron has 2 and 3 valencies. These valencies are iron variable valencies, and the elements’ valency varies for stability. The half-filled subshell has more exchange energy than the compound.

How to determine element valency

The periodic table arranges elements according to atomic numbers, making it easy to determine an element’s valency. There are a number of steps involved, including You must first write out the electronic configuration for each element and determine the number of electrons in each shell, particularly the last one.

If the number of electrons in the last shell is less than or equal to four, then the valency of that element will be equal to the number of electrons in the last shell because valency is the combining capacity of an element.

If the number of valence electrons is greater than 4, the valency of electrons will be equal to the difference between 8 and the number of electrons in the valence shell, because the atom tries to get an octet configuration to become stable. Hence valency will be equal to 8 – the number of electrons in the valence shell.

Types of Valency

Electrovalency

Valence is the number of electric charges an atom gains or losses  when electrons transfer between elements during the formation of an ionic bond. Elements with a negative electrovalency gain electrons, and positive electrovalency lose them.

Consider the following examples:

Sodium chloride (NaCl)

Sodium loses one electron to generate a Neon gas configuration, while chlorine gains one electron and becomes stable. As sodium loses an electron, its electrovalency is 1, whereas chlorine gains an electron, its electrovalency is -1. Na has positive electrovalency, and cl has negative electrovalency.

Magnesium chloride (MgCl2)

Because the Neon gas configuration is the nearest electronic configuration, magnesium must give up two electrons to become stable, while chlorine must gain one electron to be stable. While magnesium loses two electrons, chlorine gains one and hence has a negative electrovalency of 1.

Covalency

Valence is the number of electron pairs an atom can share in a chemical substance. The covalent bond relates to covalency, and atoms that share 2 electrons have a covalency of 2.

Consider these examples:

CH4

Carbon shares 4 electrons with hydrogen; hence its covalency in methane is 4. Each hydrogen atom in methane has a Covalency of 1.

Nitrogen

A nitrogen molecule’s two nitrogen atoms share 3 electrons. Nitrogen has covalency 3.

How do valence and electrons relate?

Electronics are responsible for chemical bonds and atom contacts in the Rutherford nuclear atom model. In 1916, Gilbert N. Lewis said that atoms prefer to form a stable octet of 8 valence-shell electrons. According to Lewis, covalent bonding creates octets by sharing electrons, whereas ionic bonding produces octets by transferring electrons from one atom to the next.

“The number of pairs of electrons that each particular atom shares with neighbouring atoms is covalence of that atom,” wrote Irving Langmuir in 1919. The atoms must have the same valence in a covalent bond since co- implies “together.” Since then, covalent bonds have replaced valence in higher-level studies due to advances in chemical bonding theory, although valence is still widely used in introductory studies as a heuristic introduction to the subject.

Conclusion

The electronic configurations of certain elements create variable valency. An element’s atom may lose more electrons than it has in its valence shell, causing more than one or variable valency.

The outermost orbital of transition metals is the s-orbital, and the penultimate orbital is the d-orbital. In accordance with Aufbau’s principle, iron has an atomic number of 26 and an electronic configuration of 1s2 2s2 2p6 3s2 3p6 4s2 3d6 and to get the same result, you can use 1s2 2s2 2p6 3s2 3p6 3d6 4s2 instead. As a result, the element has a variable valency due to its various electronic configurations. In addition, because the outermost electron shell of an atom must contain a total of 2 or 8 electrons when Fe or another transition metal reacts with another, the transition atoms must share their electrons by their needs.