Dot and cross sim
Dots and crosses are only bookkeeping: all electrons are the same, and the two marks show which atom each one came from.
Dot and cross · covers the GCSE, IGCSE, O-Level topic
What the sim shows
Dots and crosses are only bookkeeping: all electrons are the same, and the two marks show which atom each one came from. Ionic bonding: the metal atom loses its outer electrons and the non-metal atom gains them, so both end with a full outer shell. Electrons lost = electrons gained, which fixes the formula. Each ion is drawn in square brackets with its charge outside, at the top right. A positive ion is drawn with its new outer shell, the full shell inside (Na⁺ is 2,8). Covalent bonding: non-metal atoms share pairs of electrons, one electron from each atom. One shared pair is a single bond, two a double bond, three a triple bond. Hydrogen's shell is full with 2; the other outer shells here are full with 8. Covalent diagrams show outer shells only, as the lessons draw them.
Use it in your lessons
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