Molar MassMolar mass of iodine (I2)
The molar mass of iodine, I2, is 253.80 g/mol. One mole of it, which is 6.022 × 1023 molecules, has a mass of 253.80 grams.
About iodine
Iodine forms shiny grey-black crystals that turn straight into a violet vapour when warmed. It is listed here with the other two-atom elements.
The working
The formula I2 has 2 iodine atoms. Multiply each count by the atomic weight of the element and add:
| Element | Atoms | Atomic weight | Total | Share by mass |
|---|---|---|---|---|
| Iodine (I) | 2 | 126.90 | 253.800 | 100.00% |
2 × 126.90 = 253.800 g/mol
With the rounded atomic masses used in many school books (I = 127) the answer is 254 g/mol. The difference from 253.80 is too small to matter in most school sums.
Percentage composition
I2 contains only iodine, so iodine makes up 100% of its mass. Each molecule has 2 atoms, which is why the molar mass is 2 times the atomic weight 126.90.
Worked examples
Grams to moles. How many moles are in 5 g of I2? Divide the mass by the molar mass: 5 ÷ 253.80 = 0.0197 mol.
Moles to grams. What is the mass of 0.25 mol of I2? Multiply: 0.25 × 253.80 = 63.45 g.
Counting particles. 5 g contains 0.0197 mol × 6.022 × 1023 = 1.186 × 1022 molecules, and 2.373 × 1022 atoms in all.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 25.38 g |
| 0.5 mol | 126.9 g |
| 1 mol | 253.8 g |
| 2 mol | 507.6 g |
| 5 mol | 1269 g |
| Mass | Moles |
|---|---|
| 1 g | 0.00394 mol |
| 10 g | 0.0394 mol |
| 100 g | 0.394 mol |
| 1 kg | 3.94 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of I2?
The molar mass of iodine (I2) is 253.80 g/mol, or 253.800 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of I2?
100 ÷ 253.80 = 0.394 mol.
What is the mass of one molecule of I2?
Divide the molar mass by the Avogadro constant: 253.80 ÷ 6.022 × 1023 = 4.214 × 10-22 g.
Which values? This site uses the abridged standard atomic weights published by IUPAC (CIAAW), read on 12 November 2026. Your textbook or question paper may round them differently, for example H = 1 and O = 16, so its answer can differ slightly. In an exam, use the values the paper gives.