What it does
When a metal reacts with a non-metal, the metal atoms give their outer electrons to the non-metal atoms. Both end up with a full outer shell, as ions of opposite charge that attract each other: an ionic bond. This page lets you do the transfer yourself, one electron at a time:
- pick a metal (lithium, sodium, potassium, magnesium, calcium, aluminium) and a non-metal (fluorine, chlorine, oxygen, sulfur, nitrogen),
- the outer shell of each atom is drawn with the metal’s electrons as crosses (×) and the non-metal’s as dots (•),
- press Move one electron and an arrow shows where the next one goes,
- when an atom has given or taken all it needs, it is put in square brackets with its charge,
- the page explains the shells before and after, why the numbers of atoms are what they are, and gives the formula and the name.
It follows the Class 10 chapter on metals and non-metals (how metals and non-metals react, ionic compounds), and the Class 11 chapter on chemical bonding.
Once you have the ions, write the formulas of many more compounds with the formula writer; the shells come from build an atom, and which metals react most readily is shown in the reactivity series lab.
How to use it
- Choose the Metal and Non-metal. The right number of each atom is drawn: one sodium and one chlorine, but one magnesium and two chlorines.
- Press Move one electron to move them one by one, or Move them all. Start again puts them back.
- Read What happened for the shells of the atoms and ions and why the formula balances.
A worked example
Magnesium and chlorine. Magnesium (Z = 12) has shells 2, 8, 2: two outer electrons. Chlorine (Z = 17) has 2, 8, 7: it needs one more to make 8. One chlorine can only take one electron, so a magnesium atom needs two chlorine atoms. Two electrons move, giving Mg²⁺ (2, 8) and two Cl⁻ (2, 8, 8). The formula is MgCl₂, magnesium chloride.
Aluminium and oxygen is the biggest: aluminium loses 3 and oxygen gains 2, so 2 Al and 3 O balance at 6 electrons: Al₂O₃.
Tips
- Metal atoms lose all their outer electrons; non-metal atoms gain enough to reach 8.
- The total lost must equal the total gained. The formula uses the smallest numbers of atoms that make that true.
- Many ions end with the same shells as a noble gas: Na⁺, Mg²⁺, Al³⁺, F⁻ and O²⁻ are all 2, 8, like neon.
Check yourself
Four fresh questions each time: a formula (type digits normally, e.g. MgCl2), the number of electrons moved, the shells of an ion (like 2,8) and the charge on an ion. Nothing is saved.
FAQ
Are the electrons really crosses and dots? No: all electrons are the same. The marks just show where each one came from.
Why only elements up to calcium? The simple 2, 8, 8 shell rule works for them; heavier atoms fill shells in a more complicated order (Class 11).
Is this from the NCERT book? It covers the same topic with fibub’s own drawings. fibub is not part of NCERT.
Where the numbers come from
- Shell filling 2, 8, 8, 2 for elements 1 to 20, valency and ion charges, and dot-and-cross diagrams are standard school chemistry. Written for fibub.
- Checked against the known formulas NaCl, MgO, MgCl₂, Na₂O, CaF₂, Al₂O₃, AlN, Li₃N and K₂S, and for all 30 metal and non-metal pairs that charges balance and every atom gives or takes exactly its electrons.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.