Atoms and Molecules

H₂, O₂, N₂, Cl₂

Diatomic molecules contain exactly two atoms. H₂, O₂, N₂, and Cl₂ are all diatomic molecules. Helium (He) is monoatomic, existing as single atoms.

1:8

In water, the mass ratio of hydrogen to oxygen is always 1:8. This means for every 1 gram of hydrogen, there are 8 grams of oxygen, regardless of the source of water.

All matter is made of atoms, Atoms are indivisible, Atoms of the same element are identical, Atoms combine in simple whole number ratios

Dalton's atomic theory states that all matter is made of indivisible atoms, atoms of the same element are identical, and they combine in simple ratios. Atoms cannot be created or destroyed in chemical reactions.

CaO

Calcium oxide has the formula CaO. Calcium has a valency of +2 and oxygen has a valency of -2, so they combine in a 1:1 ratio to form CaO.