My students found these illustrations helpful in understanding the differences in bonding behavior of molecules vs ionic compounds. I included these on a review sheet that was previously posted without illustrations. They adamantly insisted I update the posted review sheet with these pictures!
The Na-Cl bond is electrostatic in nature with the positively charged sodium clinging to the negatively charged chlorine. While they "cling" together, there is no overlap of their orbitals. This is in contrast to the carbon dioxide where the orbitals are totally intertwined with each other. You can see that the atoms (represented by balls) are not distinct circles but circles that are welded together to cover up part of the diameter of each. This represents the sharing of electrons in covalent bonding.
The HF bond represents the bonding of an acid, which is technically a molecular bond as well.
My question for the students was this: What is CaCO3? Can you tell by the picture and/or the type of elements in the compound whether it is ionic or covalent?