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The valency of an element is a measure of its combining capacity and can be defined as

The valency of an element is a measure of its combining capacity and can be defined as

the number of electrons that must be lost or gained by an atom to obtain a stable electron configuration.

The oxidation state of an atom is the number of electrons lost or gained by it.

Oxidation State and valency are one of the most fundamental properties of elements and can be studied with the help of electron configurations.

Electrons that are found in the outermost shell are generally known as valence electrons and the number of valence electrons determines the valency (or valence) of an atom.

The general oxidation state of the elements of the periodic table is illustrated in the chart provided below.

The valency of the first 30 elements of the periodic table is given below.

While moving left to right across a period, the number of valence electrons of elements increases and varies between 1 to 8. But the valency of elements, when combined with H or O first, increases from 1 to 4 and then it reduces to zero. Consider two compounds containing oxygen Na 2 O and F 2 O. In F 2 O, the electronegativity of F is more than oxygen. Hence, each of F atoms will attract one electron from oxygen i.e. F will show -1 oxidation state and O will show +2 oxidation state. Whereas, in the case of Na 2 O, oxygen is highly electronegative than sodium atom. So oxygen will attract two electrons from each sodium atom showing -2 oxidation state and Na will have +1 oxidation state. The oxidation state of the element represents the charge possessed by an atom due t o the loss or gain of electrons (due to the electronegativity difference between the combining atoms) in the molecule.

As we move down in a group the number of valence electrons does not change. Hence, all the elements of one group have the same valency.

To learn more about the periodicity in the properties of elements the trends in the oxidation states of elements in the periodic table, –