The metal has lost electrons and forms positive ions, also called cations. The non-metal has gained electrons and so forms negative ions, also called anions. The ions have opposite charges, so are strongly attracted to each other. These electrostatic attractions make ionic bonding.
A dot and cross diagram can model the transfer of electrons from metal atoms to non-metal atoms. The electrons in one atom are shown as dots, and the electrons in the other atom are shown as crosses. For example, when sodium reacts with chlorine, electrons transfer from sodium atoms to chlorine atoms.
When drawing a dot and cross diagram, it is usual to show:
The slideshow shows dot and cross diagrams for the ions in sodium chloride, magnesium oxide and calcium chloride.