How the OCR sheet is laid out
OCR puts the atomic number at the top of each box. The symbol and name follow, and the relative atomic mass sits at the bottom. AQA and Edexcel print it the other way up, so check which number you are reading.
Along the top, OCR numbers every column from 1 to 18. Above the main groups it also prints (1) to (7) and (0).
One decimal place for every mass
Every OCR mass has one decimal place, so hydrogen is 1.0 and magnesium is 24.3. A sum of these numbers also has one decimal place.
Chlorine at 35.5 and copper at 63.5 are the same on every board. Most other elements differ a little from the AQA GCSE table, which rounds to whole numbers.
Empty boxes on the OCR table
OCR prints 67 masses. Technetium, polonium, astatine and radon have a box with a symbol and name, but no mass. The same goes for francium, radium and the heavy elements in period 7.
The lanthanides and actinides get no boxes of their own. In their place, the third column says 57-71 in period 6 and 89-103 in period 7. Elements 113, 115, 117 and 118 are not on the sheet.
The calculator on this page tells you when a formula uses one of these elements, since there is no OCR mass to work with.
Working out Mr with OCR numbers
Magnesium oxide, MgO, has one of each atom, so its Mr is 24.3 + 16.0 = 40.3. Carbon dioxide, CO2, has two oxygen atoms.
- C: 1 × 12.0 = 12.0
- O: 2 × 16.0 = 32.0
- Mr of CO2 = 12.0 + 32.0 = 44.0
The OCR 21st Century page uses the same sheet, and the hub page compares every board. For practice away from the table, try our science games.
OCR Gateway periodic table questions
Why are some boxes on the OCR periodic table empty?
OCR gives no mass for technetium, polonium, astatine, radon or any element in period 7. Their boxes show only the symbol, name and atomic number.
Does OCR Gateway use the same periodic table as OCR 21st Century?
Yes. The Chemistry A (J248) and Chemistry B (J258) data sheets carry an identical periodic table.
Should I round OCR masses to whole numbers?
No. Use the numbers as OCR prints them, with their one decimal place, so water comes out at 18.0.