Counting the number of electrons in an atom
3 marks · EasyThe table below shows the atomic numbers for four elements.
| Element | Atomic number |
|---|---|
| Phosphorus | 15 |
| Sodium | 11 |
| Nitrogen | 7 |
| Argon | 18 |
For each element, state the number of electrons in its neutral atom.
Explain briefly how you worked out your answers.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) — · must show Phosphorus: 15 electrons, Sodium: 11 electrons, Nitrogen: 7 electrons, Argon: 18 electrons
(b) The number of electrons in a neutral atom is equal to the atomic number. · must show number of electrons equals atomic number
Must show: correct numbers from table, explanation of how atomic number gives electrons
Common mistakes: Giving number of protons and neutrons
Show mark scheme and worked solution
Marking points
B1 (a) · 2 marks · All 4 elements with correct number of electrons (1 mark for any 2 or 3 correct, 2 marks for all 4 correct).
B2 (b) · 1 mark · States that number of electrons equals atomic number for a neutral atom.
Worked solution
| Element | Number of electrons |
|---|---|
| Phosphorus | 15 |
| Sodium | 11 |
| Nitrogen | 7 |
| Argon | 18 |
I worked out the answers by using the rule that in a neutral atom, the number of electrons equals the atomic number.