Valence Electrons: Characteristics and Valency Determination

The s and p electrons in the outermost shell are known as valence electrons. The core electrons are the ones that are present in the inner shell. While studying the atom of an element, we get to know about the tiny subatomic particles that are known as valence electrons.

The arrangement of valence electrons is in different orbital shells and the particles are mostly negatively charged. Further, these particles are in charge of the coordination of interaction between atoms and the formation of chemical bonds. Not all electrons are associated with the atom, however. Only the electrons in the outermost shell can participate in forming a chemical bond or a molecule. Electrons of such type are called valence electrons.

Dalton’s atomic theory suggested that the atom was indestructible and indivisible. His theory resulted in a failure when the two particles, protons and electrons were discovered inside the atom. Many scientists came forward with their models for an atom after this discovery.

Read Also: Variable Valency

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Valence Electrons

The number of electrons an atom must gain or lose in order to attain the nearest noble gas or inert gas electronic configuration is known as valence. Valence electrons are the electrons in the outer shell that are not filled.

Most chemical reactions involve valence electrons because the energy they contain is more than that contained by the electrons in the inner orbits. Meanwhile, the number of valence electrons also helps in the determination of the chemical properties of a specific element such as the formation of bonds with other elements and/or its valence or valency. It is also instrumental in giving an idea of how readily the atoms can form bonds, the number of atoms that can take part, and the number of unpaired electrons.

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Characteristics of a Valence Electron

The chemical bonding and the reaction of an atom involve electrons. It is said that they occupy orbitals in an atom. The total valence electrons of an atom can be determined from the periodic table because it is equal to the group number of the atom. Atoms have the most stability if they have a filled valence shell of electrons. The transfer and share of electrons between atoms happens in such a way that a filled shell of electrons can be attained by them.

Some key characteristics of a valence electron are as follows:

• The valence electron exists only in the outermost electron shell for the elements in the main group.
• A valence electron can exist within the inner shell of a transition metal.
• An atom with a closed shell of valence electrons usually remains chemically inert.
• A valence electron can absorb or release energy in the form of a photon.
• In an element, the electrical conductivity can be found by valence electrons. The element can be a metal, non-metal or a metalloid depending on the nature of the elements.

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Valency

From the scheme laid down by Bohr and Bury, we know that the outermost shell of an atom can contain a maximum of eight electrons. The atoms of elements that have eight electrons in their last shell have zero capacity to combine or their valency is zero. Helium atom has two electrons in its outermost shell and all the other elements have atoms that have eight electrons in their outermost shells.

The tendency of atoms to combine and form molecules of the same or different elements was explained as an attempt to attain a fully filled outermost shell. An outermost shell that has eight electrons is said to possess an octet. Atoms would thus react in such a way that they would achieve octet in the outermost shell. This is carried out by sharing, losing, or by gaining electrons. The number of electrons shared, lost, or gained to achieve the octet set of electrons at the outermost shell indicates the capacity of combination of the element or their valency directly.

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Determination of Valence Electrons

Checking out the place of the elements in the periodic table is one of the easiest ways to find electrons. The valence electrons of an element can be determined by closely examining the vertical column where the elements are grouped in. The number of valence electrons that an element has can be identified by looking at the group number.

The list of the number of valence electrons present in the different groups is shown in the following data:

Electronic configuration can also be employed for determination of the valence electrons.

If the transition metals (groups 3 – 12) are taken, it can complicate the process of finding the valence electron. The structure of the atom of these elements is rigid and the d subshell is partially complete and sits lower than the outer shell.

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Things to Remember

• The outermost shell of an atom can carry a maximum of 8 electrons.
• For attaining stability, atoms gain, lose, or share electrons for completing the octet.
• Only the electrons present in outermost orbit will take part in all chemical reactions.
• The number of atoms present in a molecule of an element or a compound is known as the atomicity of an atom.
• The capacity of the elements of an atom to combine is known as valency.
• An atom can be considered chemically inert if it consists of a closed shell of valence electrons.
• The ions that have more than one atom (same kind or may be of different kind) and behave as a single unit are known as polyatomic ions.

Read Also: Valence Bond Theory

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