Calculate the number of protons, neutrons and electrons in the \(^{{\text{26}}}{\text{M}}{{\text{g}}^ + }\) ion.

The sample contained the three isotopes \(^{{\text{24}}}{\text{Mg}}\), \(^{{\text{25}}}{\text{Mg}}\) and \(^{{\text{26}}}{\text{Mg}}\). The relative percentage abundances of \(^{{\text{25}}}{\text{Mg}}\) and \(^{{\text{26}}}{\text{Mg}}\) are 10.00% and 11.01% respectively. Calculate the relative atomic mass \({\text{(}}{{\text{A}}_r}{\text{)}}\) of magnesium, accurate to two decimal places.

Protons: 12

Neutrons: 14

Electrons: 11

Award [2] for three correct answers.

Award [1] for two correct answers.

Award [0] for one correct answer.

\(^{{\text{24}}}{\text{Mg}} = (100 - 10.00 - 11.01 = ){\text{ }}78.99\% \);

\({A_r} = (24 \times 0.7899 + 25 \times 0.1000 + 26 \times 0.1101 = ){\text{ }}24.32\);

Award [2] for correct final answer which must be to two decimal places.

Do not accept data booklet value of 24.31.

The question on the structure of atoms generally scored well. The workings of the mass spectrometer was less well known; with many getting confused with the role of the magnetic and electric fields. The calculation of the A_r was done very well. 

The question on the structure of atoms generally scored well. The workings of the mass spectrometer was less well known; with many getting confused with the role of the magnetic and electric fields. The calculation of the A_r was done very well.