1 Define isotopes as different atoms of the same element that have the same number of protons but different numbers of neutrons

Example: carbon- 12, carbon-13 and carbon-14 are isotopes of carbon as they have same proton number of 6. But carbon- 12, carbon-13 and carbon-14 have 6 neutrons, 7 neutrons and 8 neutrons respectively.

2 Interpret and use symbols for atoms and ions 

 

3 State that isotopes of the same element have the same chemical properties because they have the same number of electrons and
therefore the same electronic configuration

Example: carbon- 12, carbon-13 and carbon-14 are isotopes of carbon as they have same proton number of 6. All of their atoms have 6 electrons. Their electronic configuration is 2.4. They have the same chemical properties as they all have 4 valence electrons but different physical properties since their mass numbers are different.

4 Calculate the relative atomic mass of an element from the relative masses and abundances of its isotopes

Mulitply the relative abundance in decimals (usually given in percentage) by the respective isotopic mass and add the values together. 

For example : Chlorine-35 has abundance of 75% and chlorine-37 has abundance of 25%. Calculate relative atomic mass of chlorine.

75% is 0.75 and 25% is 0.25 

relative atomic mass of chlorine = (0.75 X 35) + (0.25 X 37) = 35.5