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When you write H2SO4 or CuSO4 you are using a system one Swedish chemist proposed in a journal article published in 1813 and 1814. Before Berzelius, chemists used drawn signs, some of which, he wrote, went back to the alchemists. This post covers who he was, the rules he set, what has changed since, and a worked example that turns a formula into numbers.
Who was Berzelius?
The Science History Institute profile gives his dates as 1779 to 1848. While studying medicine at Uppsala he read about Volta's electric pile and built one himself. In 1807 he became a professor at the Medical College in Stockholm, which became the Karolinska Institute, and from 1818 to 1848 he was Permanent Secretary of the Royal Swedish Academy of Sciences.
He was a careful, large-scale experimenter. The profile says he ran programmes of hundreds of experiments that firmly established the law of constant proportions for inorganic compounds, discovered cerium, selenium and thorium, and determined the atomic weights of nearly all the elements then known.
Why did chemistry need new symbols?
Berzelius explained his reasons in the "Essay on the Cause of Chemical Proportions", published in Annals of Philosophy in 1813 and 1814. An excerpt is reproduced by Classic Chemistry. The older signs, he wrote, were well made but "of no use; because it is easier to write an abbreviated word than to draw a figure". His proposal was blunt: "The chemical signs ought to be letters, for the greater facility of writing, and not to disfigure a printed book."
What were his rules?
He set out three rules in the same section:
Take "the initial letter of the Latin name of each elementary substance". So oxygen is O and sulphur is S.
If a metal shares its first letter with another element, write the first two letters: Co for cobaltum, since carbon is already C.
If the first two letters are also shared, add the first consonant the names do not share. Stibium (antimony) and stannum (tin) both begin "St", so he wrote St for stibium and Sn for stannum. Antimony later became Sb.
The Latin rule explains symbols that puzzle students today: Cu from cuprum and Ag from argentum. He then combined symbols. Water was "2H + O", and copper sulphate was written CuO + SO3, as an oxide of copper joined to an oxide of sulphur.
What has changed since then?
Not every symbol survived. The Classic Chemistry editor notes that in this paper Berzelius used Po for potassium, So for sodium and Ms for magnesium. Today these are K (kalium), Na (natrium) and Mg. Chemists also stopped writing a compound as one oxide plus another, so CuO + SO3 became CuSO4. The letters-from-Latin idea, though, is the one in your book.
Worked example: from formula to percentages
Find the percentage of each element in copper sulphate, CuSO4. Using the IUPAC abridged atomic weights (Cu 63.546, S 32.06, O 15.999):
Read the formula. One Cu, one S, four O. The subscript 4 belongs to O only.
Molar mass. 63.546 + 32.06 + 4 × 15.999 = 63.546 + 32.06 + 63.996 = 159.602 g/mol.
Percentages. Cu: 63.546 / 159.602 × 100 = 39.8%. S: 32.06 / 159.602 × 100 = 20.1%. O: 63.996 / 159.602 × 100 = 40.1%.
Check. 39.8 + 20.1 + 40.1 = 100.0. If your total is far from 100, a subscript was misread.
The JEE (Main) 2026 syllabus lists "percentage composition, empirical and molecular formulae" in its first chemistry unit, and the NCERT Class 11 chapter Some Basic Concepts of Chemistry works similar examples. Our guide to empirical and molecular formula problems runs the calculation the other way.
Which mistakes does this help you avoid?
Applying a subscript to the wrong symbol. In CuSO4 the 4 is for oxygen only. In Ca(OH)2 the 2 multiplies everything inside the brackets.
Case errors. Co is cobalt; CO is carbon monoxide. The second letter of a symbol is always lower case.
Guessing symbols from English names. Learn the Latin ones: Na, K, Fe, Cu, Ag, Sn, Sb, Au, Hg, Pb.
What can a student take from Berzelius's way of working?
Make notation serve the work. He changed the symbols because he had so many compounds to record that pictures slowed him down.
Repeat until the pattern is firm. Hundreds of analyses, not one, made the case for constant proportions. Our post on Joseph Proust and definite proportions covers the other half of that story.
Keep the system simple. Three short rules covered every element he knew.
If formulas and molar masses are where you lose marks, the Fermi Problem Library has worked problems with a step-by-step solver that explains the reasoning rather than printing an answer.
Try it now: find the percentage of water in CuSO4·5H2O, writing each molar mass out in full.
