Imagine there are various people having different pattern of hands. Some have no hands and some have one, some two and others three. Few have four and no one has more than four. The person with four hands can hold hands of four others at a same time, while the one with no hands can never hold any hand. In this manner some atoms can hold one electron, some can hold two, some can hold three, some can hold four and some cannot hold any electron. This property is called valency.
WHAT MAKES ATOMS STICK TOGETHER?
Electrons carry a negative electric charge, and protons carry a positive charge. The attraction between them holds electrons in orbits.
This combining property of an atom is called as Valency. It is a measure of how many hydrogen atoms it can combine with. For example: oxygen can combine with two hydrogen atoms and create water molecule, the valency of oxygen atom is two. In case of chlorine, it can combine with only one hydrogen to create HCl (hydrochloric acid) here the valency of chlorine is one. Methane has one carbon atom combining with four hydrogen atoms to form carbon molecule is methane (CH4). Can you guess the valency of Carbon in methane? In ammonia molecule, Nitrogen combines with three hydrogen atoms. What is the valency of Nitrogen in ammonia?
Valency is defined as the combining capacity of an element. Atoms of different elements combine with each other to form molecules. Valency determines the number of atoms of an element that combines with atom or atoms of another type.
The element having valency one is called monovalent. For example: Hydrogen and Sodium. The elements having valency two are called divalent. For example: Oxygen and Beryllium. The elements having valency three are called trivalent. For example: Nitrogen and Aluminium. Some elements exhibits more than one valency. For example: Iron combines with oxygen to form two types ferrous oxide (exhibits valency 2) and ferric oxide (exhibits valency 3), however we will study about them later.
When atoms of different elements combine with each other then molecules of compounds are formed. In these instances, it is necessary to know the valancies of those elements. For example:
1 2Na+ Cl2 ---------- 2NaCl
Valency 1+ 1
Here, the valancies of both sodium and chlorine are 1.
Remember The valency of element Na is 1
The valency of element Cl is 1
Then, the molecular formula will be
Symbol of Elements Na Cl Molecular Formula
Radicals and ions11
2 Mg + Cl2---------- Mg Cl2
Valency 2 1
Here , the valency of magnesium is 2 and that of Cl is 1.
Elements and their symbols with their atomic number and mass number and valency.