Atomic structure and periodic position practice

Enter an element, a nucleon number and a charge, and this tool gives you the protons, neutrons, electrons, shell arrangement, group and period. It is for students who can recite the periodic table but freeze when a question asks for the electrons in an ion.

Who is this tool for?

It suits Form 4 and Form 5 students learning atomic structure in Science or Chemistry. It also helps anyone revising for a test who wants to check their own counting.

The quiz gives new questions each time, so you can practise without a textbook open.

How do I use it?

1. Choose the calculator tab and pick an element from the list.
2. Check the nucleon number. The tool fills in the usual value, and you can change it for an isotope.
3. Pick the charge of the particle, from −3 to +3.
4. Press Show structure and read the table, the diagram and the working.
5. Switch to the quiz tab, answer the six questions, then press Check answers and read each explanation.

How does it work?

Every number comes from three rules. Protons equal the proton number. Neutrons equal the nucleon number minus the proton number. Electrons equal the protons minus the charge.

Electrons then fill shells in order: 2, then up to 8, then up to 8, then the fourth shell. The number of shells gives the period. The electrons in the outer shell of the neutral atom give the group, and helium is placed in group 18.

A short worked example

Take a magnesium ion with nucleon number 24 and charge +2.

Protons = 12, and neutrons = 24 − 12 = 12. Electrons = 12 − 2 = 10, arranged 2.8.

The neutral magnesium atom is 2.8.2, so it has three shells and two outer electrons. That puts magnesium in period 3, group 2.

A frequent mistake is to use the ion’s 2.8 arrangement to find the group. Always use the neutral atom to find the position.

What are the limits?

The tool covers elements 1 to 20 only, using the shell model taught in school. It does not check that the isotope you type exists in nature.

A nucleon number smaller than the proton number would give a negative neutron count, so the tool rejects it with a message. It also rejects a charge that would leave a negative number of electrons.

Where does this help in your subjects?

Use it alongside reading atomic structure information in Science and interpreting isotopes and relative atomic mass. The matter and atomic structure practice gives longer exam-style questions.

For the next step, see explaining trends using atomic structure and predicting simple reactions from periodic position. If you want a teacher to work through it with you, read about SPM Chemistry tuition and the one-hour trial class (from RM50).