Chemical bonds form when electrons pair ("Skeletal chemistry" 3 of 9)
"Now we have atoms, we can bring them together to form the next level of structure, molecules. The unifying idea here is the tendency (governed by considerations of energy minimisation again under the constraint of the Pauli principle) of electrons to pair."
Periodic Table
This Periodic Table from Germany not only has visual images of the atoms and ions, it also has the basic rules for thinking about chemical bonds: "Metal atoms can be combined mainly to crystal packings (left-left). Non-metal atoms can be combined mainly to molecules (right-right). Metal ions and non-metal ions can be combined to crystal packings (left-right)."
Atoms and Matter (K-2)
Using Play-Doh to model atoms makes it easier to visualize "electron clouds" of two atoms overlapping to create the unified cloud of a molecule.
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Bonding Triangle
Imagine the three corners of a triangle representing metallic, covalent, and ionic bonds. Bonds between different atoms can be represented within the triangle (and along the edges) to further explore their relationships. This site traces the bonding triangle's history.
Self-Assembly Game
Atomic relationships can quickly lead to complexity. In this activity learners hold hands to see how simple bonding relationships (grab a right hand with your right hand, and left with left) cause complex patterns (students end up facing alternating ways).
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"Skeletal chemistry" article
This is one of the nine central ideas that Peter Atkins lays out in his 2005 article, "Skeletal chemistry." Each of the other ideas has its own list in SMILE.