Question

Regarding covalency which of the following statements is wrong? (1) In covalency, sharing of electrons takes place. (2) Maximum covalency is restricted to \(8 .\) (3) Covalency is the number of electron pairs shared by an atom. (4) Covalency of an atom is equal to the number of electrons contributed by an atom in the formation of covalent bonds.

Short answer

Statement 2 is wrong.

Step-by-step solution

Understanding Covalency

Covalency refers to the sharing of electron pairs between atoms to form a molecule. This bonding can be single, double, or triple depending on the number of shared electron pairs.

Evaluating Statement 1

Statement 1: 'In covalency, sharing of electrons takes place.' This is true, as covalent bonds are characterized by the sharing of electrons between atoms.

Evaluating Statement 2

Statement 2: 'Maximum covalency is restricted to 8.' This statement is incorrect. Some elements, especially those in the third period and below (like phosphorus, sulfur, etc.), can exhibit expanded valence and higher covalency than 8.

Evaluating Statement 3

Statement 3: 'Covalency is the number of electron pairs shared by an atom.' This is also true. Covalency describes the number of shared electron pairs forming covalent bonds.

Evaluating Statement 4

Statement 4: 'Covalency of an atom is equal to the number of electrons contributed by an atom in the formation of covalent bonds.' This statement is true, as the covalency can be defined by the number of electrons an atom shares in covalent bond formation.

Key concepts

Electrons Sharing

Electrons sharing is a fundamental concept in chemistry, particularly when talking about covalent bonds. When atoms form covalent bonds, they achieve stability by sharing their outermost electrons, or valence electrons. These shared electrons allow atoms to achieve a full outer energy level, similar to the electron configuration of noble gases.
For instance, in a molecule of water (H2O), each hydrogen atom shares one electron with the oxygen atom. The oxygen atom, in turn, shares one of its electrons with each hydrogen, resulting in a stable electron arrangement for all involved atoms.
So, a covalent bond is essentially like a handshake where each atom contributes an electron to be shared in the bond. This mutual sharing creates a more stable arrangement for the atoms involved.

Covalent Bonds

Covalent bonds are the type of chemical bonds formed through the sharing of electron pairs between atoms. These bonds are strong and stable, playing a crucial role in the structures of a wide array of compounds.
A single covalent bond involves one pair of shared electrons, a double bond involves two pairs, and a triple bond involves three pairs. The type and number of bonds influence the properties and stability of the molecules. For example:

• Single bonds, like those in a molecule of methane (CH4), involve one electron pair shared between the carbon and each hydrogen atom.
• Double bonds, such as those in oxygen (O2), involve two pairs of electrons shared between two oxygen atoms.
• Triple bonds, found in nitrogen (N2), involve three pairs of electrons shared between two nitrogen atoms.

These shared pairs of electrons help the atoms involved to fulfill the octet rule, making the molecules more stable.

Expanded Valence

The concept of expanded valence is key to understanding why certain atoms can form more than eight covalent bonds. Usually, atoms strive to follow the octet rule, where they have eight electrons in their valence shell. However, elements in the third period and beyond of the periodic table have access to d-orbitals, allowing them to hold more than eight electrons.
For example:

• Phosphorus in phosphorus pentachloride (PCl5) shares five electron pairs, resulting in ten electrons around the phosphorus atom.
• Sulfur in sulfur hexafluoride (SF6) shares six electron pairs, accumulating twelve electrons around the sulfur atom.

This ability to hold more than eight electrons is called an expanded valence, and it explains why some elements defy the typical eight-electron limit. This expands the range of possible molecular structures and the diversity of chemical compounds.
So, while the octet rule is a handy guideline, it’s not an absolute limit for every element.