Atoms and Molecules

All matter is made of tiny particles called atoms, Atoms are indivisible and cannot be created or destroyed, Atoms of the same element are identical in mass, Atoms combine in simple whole number ratios

Dalton's atomic theory has several postulates including that all matter is made of atoms, atoms are indivisible, atoms of the same element are identical, and they combine in simple ratios. However, most atoms cannot exist independently in nature.

Oxygen (O₂), Hydrogen (H₂), Nitrogen (N₂)

Diatomic molecules contain exactly two atoms. O₂, H₂, and N₂ are diatomic. Argon is monoatomic (single atom) and ozone is triatomic (three atoms).

4

Atomicity is the number of atoms in a molecule. Phosphorus exists as P₄ molecules, so its atomicity is 4. This is also called tetra-atomic.

1:8

In water, the mass ratio of hydrogen to oxygen is always 1:8. This demonstrates the Law of Constant Proportions - elements in a compound are always present in definite proportions by mass.