Atoms combine to form molecules — and the number and type of atoms in a molecule determines its mass. Learn to calculate it.
An atom is the smallest unit of an element. A molecule forms when two or more atoms join together — these can be atoms of the same element, or different elements.
Is O₂ (the oxygen gas we breathe) made of one type of atom or two different types?
One type — O₂ is made of two oxygen atoms joined together
The molecular mass of a compound is the sum of the atomic masses of all the atoms in its formula. (Using atomic masses: H=1, C=12, O=16, Na=23, Cl=35.5)
Find the molecular mass of water, H₂O.
2 hydrogen atoms + 1 oxygen atom = (2×1) + 16 = 18
Find the molecular mass of carbon dioxide, CO₂.
1 carbon atom + 2 oxygen atoms = 12 + (2×16) = 44
1. What is a molecule?
2. Find the molecular mass of NaCl (Na=23, Cl=35.5).
3. Find the molecular mass of methane, CH4 (C=12, H=1).
4. Is N2 (nitrogen gas) made of atoms of one element or two different elements?
5. Find the molecular mass of ammonia, NH3 (N=14, H=1).