British Sign Language Glossaries of Curriculum Terms

BSL Chemistry Glossary - relative atomic mass - Definition

Here is the periodic table. Each element has an atomic number which is displayed at the top of its chemical symbol. Have a look below each chemical symbol. The numbers look different - some even have multiple decimal places! Have a look more closely.

Now I'm going to choose one as an example. Copper's chemical symbol is Cu. It has an atomic number of 29 and a mass number of 63. However, here we have another molecule of Copper which has the same atomic number but a different mass number! We must add 69&percent; of the atomic mass of the first molecule to 31% of the atomic mass of the other. I'm now going to work it out. That gives us a total of 63.5 - that is the relative atomic mass.

Let's go back to the periodic table. The reason there are variations in the mass number of each element is because some elements can have two, three or even four isotopes with different quantities of each! Working out the quantity of each isotope and adding it together gives you the R.A.M.