Atomicity — lesson. Science State Board, Class 7.

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We know the difference between an atom, an element and a compound. Let us now learn about the term called 'atomicity'.

In chemistry, atomicity refers to the total number of atoms present in a single molecule of an element, compound, or substance. The number of atoms present in a single molecule is termed its atomicity.

We can distinguish the molecules respective to the number of elements they combined to form a molecule.
Let's look at how to figure out while calculating the atomicity of elements and compounds:

Example:

$O + O \rightarrow O_2$

Here,

$O$ refers to Oxygen atom.

Therefore, to calculate the atomicity, simply add the number of atoms together

$1 + 1 \ = 2$

Oxygen is a diatomic molecule, meaning that each molecule contains two atoms, giving it an atomicity of two.

$Cl + Cl \rightarrow Cl_2$

Here,

$Cl$ refers to Chlorine atom.

$1 + 1 \ = 2$

Chlorine is a diatomic molecule. It means that each molecule contains two atoms, giving it an atomicity of two.

$Na$

Here,

$Na$ refers to sodium atom.

$1$ atom.

Sodium is a monoatomic element. It means that each molecule contains one atom, giving it atomicity of one.

For a molecule with multiple elements,

$O_2 + O \rightarrow O_3$

Here,

$O$ refers to Oxygen atom, and

$O_2$ refers to oxygen molecule.

$2 + 1 \ = 3$

Ozone is a triatomic molecule, meaning that each molecule contains three atoms, giving it an atomicity of three.

$C + O_2 \rightarrow CO_2$

Here,

$C$ refers to Carbon atom, and

$O_2$ refers to oxygen molecule.

$1 + 2 \ = 3$

Carbon dioxide is a triatomic compound, meaning that each molecule contains three atoms, giving it an atomicity of three.

$H_2SO_4$

Here,

$H_2$ refers to hydrogen, and

$O_4$ refers to oxygen, and

$S$ refers to sulphur.

$2 + 1 + 4 \ = 7$

Sulphuric acid is a compound, giving it an atomicity of seven.

$H_2O$

Here,

$H_2$ refers to hydrogen, and

$O$ refers to oxygen.

$2 + 1 \ = 3$

Water is a compound, giving it an atomicity of three.

$NaCl$

Here,

$Na$ refers to sodium atom, and

$Cl$ refers to chlorine atom.

$1 + 1 \ = 2$

Sodium Chloride is a compound, giving it an atomicity of two.

Few more examples for elements and their atomicity.

Classification of elements	Name of the elements	Symbol	Atomicity
Metals	Aluminum	$Al$	$1$
	Copper	$Cu$	$1$
	Iron	$Fe$	$1$
Non-metals	Helium	$He$	$1$
	Hydrogen	$H_2$	$2$
	Nitrogen	$N_2$	$2$
	Fluorine	$F_2$	$2$
	Phosphorous	$P_4$	$4$

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6. Atomicity

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