Difference Between Valency and Covalency

Main Difference

The main difference between valency and covalency is that valency is the number of electrons present in the outermost shell of an atom, whereas covalency is the number of electron pairs that an atom can share.

Valency vs. Covalency

Valency is considered as the number of electrons that an atom gains or loses to become stable, while covalency is the highest amount of covalent bonds that an atom can produce by using its free orbitals. Valency may be equal to the number of electrons present in the valence shell or vice versa, whereas covalency is only determined by the number of electrons present in the valence shell.

Valency usually provides the required number of electrons to complete all the free orbitals; on the other hand, covalency is determined by the number of free electrons that exist in an atom. Valency is set for elements that can either create a covalent bond or an ionic bond; on the contrary, covalency can be present only for elements that can create a covalent bond between them.

Valency could either have a positive value or a negative value; conversely, covalency is generally always a positive value. Valency of Sulphur in SF6 is 2; on the flip side, the covalency of Sulphur in SF6 is 6.

Comparison Chart

ValencyCovalency
Valency is considered as the number of electrons that could either be lost or gained to complete its octet shell.Covalency is generally considered as it contains the highest amount of electrons to share with other atoms.
Relationship with Valence Electrons
May be equal to the number of electrons present in the valence shell or vice versaOnly be determined by the number of electrons present in the valence shell
Empty Orbitals
Usually provides the required amount of electrons to complete all the free orbitalsDetermined by the number of free electrons exist in an atom
Type of Bonding
Set for elements that can either create a covalent bond or an ionic bondCan be present only for elements that can create a covalent bond between them
Numerical Value
Could either have a positive value or a negative valueGenerally a positive value
Example
Valency of Sulphur is 2Covalency of Sulphur is 6

What is Valency?

The term valency means the number of electrons which an atom could either lose or gain to complete its octet shell. The electrons that are present in the outmost shell of an atom are the valence electrons. So, the number of electrons present in the valence shell of an atom is considered as the valency of a particular atom. For instance, consider hydrogen atom H, whose valency is one which could lose or can share more electrons from another atom to become stable.

Chlorine valency is one, and it has 7 electrons present in its outermost shell but chlorine gain one more electron from the other element to gain the properties of noble gas and become more stable because it is easy for chlorine atom to gain an electron from the other element rather lose its electrons. The valency of a specific atom or element could also be observed by the electronic configuration method.

Valency could either have a positive value or a negative value, which means positive sign on an atom indicates that the atom will gain electrons to become stable while the negative sign on atom indicates that the atom will remove its electrons to become stable. The periodic table in chemistry also indicates the valency of an atom. Examples of the valency of Sulphur in SF6 are 2; in H1 the valency is 1, etc.

What is Covalency?

The term covalency is defined in such a way that it is the highest amount of covalent bonds that an atom can produce by using its free orbitals. The number of valence electrons present in the outermost shell of an atom is the reason for the dependency of covalency. For instance, the number of electrons present in the valence shell of Hydrogen is one, and its covalency is also considered as one which is shared with other atoms to form a covalent bond.

Covalency is generally always a positive value. Because of the limited covalency capabilities of atoms is the main reason for the saturation of covalent bonds. Consequently, the covalency of an element is described by the total numbers of electrons present in the valence shell contributing to the development of covalent bonds.

Not only the number of electrons present in the valence shell but also the number of free orbitals of an atom are imperative in determining the covalency. Types of Covalency are constant covalency and variable covalency. Examples of the covalency of Sulphur in SF6 is 6.

Key Differences

  1. Valency is the property of electrons that an atom gains or loses to become stable, while covalency is the highest amount of covalent bonds that can atom produce by sharing electrons with its free orbitals.
  2. Valency could either be equal to the number of electrons present in the valence shell or vice versa, whereas covalency is only be determined by the number of electrons present in the valence shell.
  3. Valency usually provides all the required amount of electrons to complete all the free orbitals; on the other hand, covalency is determined by the number of free electrons that exist in an atom.
  4. Valency is used by elements that can either create a covalent bond or an ionic bond; on the contrary, covalency can be present only in elements that can create a covalent bond between them.
  5. Valency could either have a positive value or a negative value; conversely, covalency is generally always a positive value.
  6. In SF6, the valency of Sulphur is 2; on the flip side, the covalency of Sulphur is 6 in SF6.

Conclusion

The above discussion concludes that the valency is the number of electrons present in the outermost shell of an atom and gain or lose its electrons to become stable, whereas covalency is the number of the combined electron that an atom can share to form a covalent bond.

Harlon Moss

Harlon currently works as a quality moderator and content writer for Difference Wiki. He graduated from the University of California in 2010 with a degree in Computer Science. Follow him on Twitter @HarlonMoss

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