Atoms and molecules

July 17, 2018 0 Comments

# Atoms

The term Atom in the sense as we use today was first used by John Dalton in 1804 to describe the ultimate particles which constitute matter. According to Dalton, atom was the smallest particle of an element. It was the unit of chemical reaction and could not be further subdivided.
Amedeo Avogadro agreed with Dalton but he questioned the independent existence of atom. According to Avogadro, atom was the unit of chemical reaction but it was unable to exist independently. Later on it was found that atoms of some gases like helium, neon, argon, etc., could exist independently. Keeping these development in view, atoms can be defined as follows.

Atom is the smallest particle of an element and is the unit of chemical reaction. It may or may not have independent existence.

Atoms of common elements like hydrogen, oxygen, nitrogen, phosphorus, etc., cannot exist independently. However, the atoms of some elements like helium, argon, xenon, etc., poses independent existence.

# Molecules

The term molecule was first used by Avogadro to describe the smallest particle of matter which is capable of existing independently. A molecule may be defined as follows.

Molecule is the smallest particle of the substance ( element or compound ) which can exist independently.

Molecules are composed of two or more atoms of the same or different types. The molecules of gases like helium, neon, argon, krypton, etc., are composed of one atom only. This is why the atoms of these gases are capable of independent existence.

Depending upon the type of elements present in them, molecules can be classified as follows.

1) Homoatomic molecules

When a molecule is composed of atoms of the same element, it is said to be a homoatomic molecule.

2) Heteroatomic molecules

When a molecule is made of atoms of more than one type of elements, it is said to be a heteroatomic molecule.

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Neet Tyari

Some say he’s half man half fish, others say he’s more of a seventy/thirty split. Either way he’s a fishy bastard. Google