What is a Molecule? — lesson. Science CBSE, Class 9.

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எங்கள் ஆசிரியர்களுடன் 1-ஆன்-1 ஆலோசனை நேரத்தைப் பெறுங்கள். டாப்பர் ஆவதற்கு நாங்கள் பயிற்சி அளிப்போம்

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A molecule is the smallest particle of an element or compound capable of an independent life and exhibiting all of the substance's properties.

Molecule:

In general, a molecule is a set of two or more atoms that are chemically bound or held together by attractive forces.
Atoms from the same or different elements may combine to form a molecule.

Example:

For simple understanding, consider a water molecule

$H_{2} O$ ; two elements, hydrogen and oxygen atoms combined to form a water molecule.

Calcium oxide

$CaO$ contains two elements, calcium and oxygen atoms combined to form a calcium oxide molecule.

Glucose

$C_6H_{12}O_6$ contains three elements, carbon, hydrogen and oxygen atoms combined to form a glucose molecule.

Sodium chloride

$NaCl$ contains two elements; hydrogen and oxygen atoms combined to form a sodium chloride molecule.

Chlorine

$Cl_2$ contains two elements of a chlorine atom.

Oxygen

$O_2$ contains two elements of the oxygen atom.

Atomicity:

We can distinguish the molecules respective to the number of elements they combined to form a molecule. We call this atomicity .i.e. the number of atoms constituting a molecule.

The number of atoms present in a single molecule is termed as its atomicity.

Molecules of Elements:

The atoms that make up an element's molecules are all of the same nature.

Most of the elements' molecules are made up of just one electron, such as argon

$Ar$ , helium

$He$ , and so on.

Monoatomic Elements: In their molecular form, certain elements are monatomic, meaning they are made up of just one atom (mono-atomic). Helium $He$ is an example of a monoatomic element.
Diatomic Elements: If the molecule constitutes two atoms, we can classify it as a diatomic molecule. In their molecular shape, other elements have two or more atoms. For example, each molecule of hydrogen $H_2$ , oxygen $O_2$ , and chlorine $Cl_2$ , has two atoms.
Triatomic Elements: If another atom is combined with $O_{2}$ , it forms ozone $O_{3}$ , which is a triatomic molecule.

Note:

Monoatomic and diatomic molecules are more stable than triatomic molecules.

Most non-metal elements are diatomic.

Classification of elements	Name of the elements	Symbol	Atomicity
Metals	Copper	$Cu$	Monoatomic
	Aluminum	$Al$	Monoatomic
	Sodium	$Na$	Monoatomic
	Iron	$Fe$	Monoatomic
Non-metals	Nitrogen	$N_{2}$	Diatomic
	Hydrogen	$H_{2}$	Diatomic
	Oxygen	$O_{2}$	Diatomic
	Helium	$He$	Monoatomic
	Chlorine	${Cl}_{2}$	Diatomic
	Ozone	$O_{3}$	Triatomic
	Phosphorous	$P_{4}$	Tetra-atomic