How can you calculate the valency of each element ?
The valency is the number of the electrons that an atom gains, loses or even shares during a chemical reaction, The valency is the number of electrons that an atom needs to gain or lose in order to achieve noble gas electronic configuration.
In the chemical reaction, the atoms try to reach the stable state by losing their outermost electrons (as in case of the metals) or by sharing a number of electrons with other atoms (as in case of nonmetals).
The outermost electrons of an atom determine its valency, the valency of an element measures its ability to combine with the other elements, The valency is determined by the number of electrons in the outer shell of each atom of an element.
The valency of some elements in the modern periodic table
The elements in the group (1 A) in the modern periodic table have one valent electron in their outer shell, They are very active, they are mono-valent elements as they have only one electron in their outermost energy levels.
The elements of the group (7 A) are mono-valent elements as their outermost energy levels have (7) electrons, The elements in the group (18) in the modern periodic table are the noble gases which have a valence of zero as the valence shell is saturated with 8 electrons.
To determine the valency of the ionic molecule phosphorus tetraoxide (PO4 , four atoms of oxygen and one atom phosphorus) you should multiply the total valency of the four oxygen atoms (valency 2) and subtract that from the valency of the phosphorus atom (valency 5) , That reveals the valency of (PO4) is 3.
The valency of an element is always a whole number, and some elements exhibit more than one valency, they have more than one valency such as sulphur (S) is divalent, tetravalent and hexavalent.
Nitrogen (N) is trivalent and pentavalent while phosphorus (P) is trivalent and pentavalent, The valency of copper I is monovalent while the valency of copper II is divalent.
The valency of Iron [II] sulfate or ferrous sulfate is divalent as in FeSO4, the valency of iron is two while the valency of Iron [III] sulfate or ferric sulfate is trivalent as in Fe2(SO4)3, the valency of iron is three.