Valency-Radical

In chemistry, valence (sometimes called valency) is the characteristic of an element that governs the number of other atoms with which it may combine.  The phrase was coined in 1868 to indicate both the overall capacity of combining an element and the numerical magnitude of that power of combination.

The combining power of an element is known as valency. The valency of elements in the same group of the periodic table is the same. The number of electrons in an element’s outer shell determines its valency and the number of the group.The term ‘‘Radical’’ in chemistry means a specie containing an unpaired electron. For example methyl radical CH3.  .

Radical

A radical is a molecule with at least one unpaired electron, sometimes known as a free radical. Most molecules have an even number of electrons, and the covalent chemical bonds that hold the atoms in a molecule are usually made up of pairs of electrons shared by the atoms joined by the bond.

In his (failed) attempt to produce hexaphenylethane in 1900, Moses Gomberg unintentionally found natural trivalent carbon and the first radical in the modern sense.

Is there a difference between valency and radical?

The most critical distinction between radical and valency is that a radical is a chemical species with an unpaired electron. In contrast, valency is a chemical notion that characterises a chemical element’s capacity to mix with another chemical element.

What are the different kinds of valency?

There are three sorts of valency: central or classical, coordinate, and nonclassical. The first is concerned with simple compounds and their components, the second with coordination compounds, and the third with transition-metal carbonyls and related species.

• Ammonia gas is formed when one atom of nitrogen interacts with three hydrogen atoms. As a result, nitrogen has a valency of 3.

What are the different types of radicals?

There are two types of radicals: neutral radicals and charged radicals. Furthermore, sigma radicals and pi radicals are two different kinds of radicals. The sigma-radical has an unpaired electron in the sigma orbital, while the pi radical has an unpaired electron in the pi orbital.

• Here are some examples of radicals NH4+, Na+, NO3−, SO42−

• Let us now study the valency of a radical as we now know the difference between radical and valency

The amount of charge present on charged ions or radicals determines their valency. They are classified into three groups based on the charge on radicals or ions: 

• Monovalent ions 

Monovalent ions are ions with valency or ions with a single unit charge.

• Divalent

Divalent ions have a valency of two or ions with two unit charges.

• Trivalent

The ions with valency three or three-unit charge are known as Trivalent ions.

Let’s see methods with which we can calculate valency of Radicals

• By using Octet Rule

Determine the number of electrons in the outer shells of the radical elements. This may be found by counting how many columns the element appears on the periodic table as a noble gas. The cyanide radical (CN), for example, contains four outer electrons for carbon and five for nitrogen.

Covalent bonds are used to connect the atoms to share as many electrons as feasible without surpassing eight. Both carbon and nitrogen can share three electrons in cyanide. When you add these three electrons to the five electrons that nitrogen already possesses, you have an octet. Carbon has seven electrons at the end of the process.

Calculate the number of electrons that would need to be added to the molecule to create an octet for all elements. The valence of the radical is this number. In this case, one electron is required to make carbon an octet. As a result, the cyanide radical possesses a single valence.

• By using the existing chemical formula

Look for a known hydrogen-containing formula that contains the radical. 

Consider hydrogen sulphate (H2SO4) to calculate the Valency of the sulphate radical.

Calculate the number of hydrogen atoms in the formula. This is the radical’s Valency. Because H2SO4 includes two hydrogen atoms, sulphate has a valency of two. Because sulphate may form bonds with two positively charged hydrogen atoms, its Valency is commonly written as 2-.

Use a chemical with a known valence if no hydrogen-containing compound is available. Aluminium sulphate, for example, has the formula Al2(SO4)3. The valence of aluminium is 3+, and the overall valence is 6+ since there are two aluminium atoms in the formula. Because the formula contains three sulphate ions, six divided by 3 gives sulphate a valence number of 2.

Because aluminium produces positive-charged ions, the sulphate ion has a negative charge, giving the sulphate radical a 2-valency.

Examples for Valency of radicals (Monatomic cations):

For Monovalent: Hydrogen (H+), Lithium (Li+) ,Sodium (Na+), Potassium (K+),Cesium (Cs+), Silver (Ag+)

For Divalent: Beryllium (Be2+), Magnesium (Mg2+), Calcium (Ca2+), Cadmium (Cd2+), Nickel (Ni2+), Strontium (Sr2+), Barium (Ba2+).

For Trivalent: Aluminium Al3+

Conclusion:

In chemistry, valence (sometimes called valency) is the characteristic of an element that governs the number of other atoms with which it may combine. The phrase was coined in 1868 to indicate both the overall capacity of combining an element and the numerical magnitude of that power of combination.

In his failed attempt to produce hexaphenylethane in 1900, Moses Gomberg unintentionally found trivalent carbon – the first radical in the modern sense. Most molecules have an even number of electrons, and the covalent chemical bonds that hold the atoms in a molecule are usually made up of pairs of electrons.

There are three sorts of valency: central or classical, coordinate, and nonclassical. The first is concerned with simple compounds and their components, the second with coordination compounds, and the third with transition-metal carbonyls and related species. There are two types of radicals: neutral radicals and charged radicals. 

Two methods to calculate the valency of the radical 

• By using Octet Rule
• By using the existing chemical formula