Isotopes and relative atomic mass

Explain the meaning of the term isotope

Isotopes are different atomic forms of the same element, which have the same number of protons but different number of neutron

What must isotopes have?

Same proton number but different mass number

Example of a pair of isotopes:

Carbon -12, carbon- 13

What does relative atomic mass take into account?

All stable isotopes

What does Ar describe?

How heavy different atoms are compared with the mass of an atom of carbon-12. So carbon-12 has an Ar of exactly 12

What does Ar allow for?

It’s the average mass of all the isotopes of an element. It has to allow for the relative mass of each isotope and its relative abundance

What does relative abundance mean?

How much there is of each isotope compared tot he total amount of the element in the world. This can be a ratio, a fraction or a percentage

How do you calculate relative atomic mass?

Multiply the mass of each isotope buy its relative abundance

Add those together

Divide by the sum of the relative abundances

E.g. Ar = (35.0 × 3) + (37.0 × 1) / 3 + 1 = 35.5