Re: What causes the molecular attractive and repelling forces.

Thank you for your question. The answer is quite complex and advanced so I’ll try to give you a simple picture.

You have probably heard of atoms and molecules. You probably also know they are made of things called protons and electrons (and neutrons, but they’re not important here).

The protons have positive charges while the electrons are negatively charged. In some substances there are molecules, where the atoms are joined together in groups. The electrons are always moving around and the molecules may have bits that are more positive than others, while some bits are negative for a moment. This means the molecules are like little magnets with N and S poles that attract. However, if they get too close the clouds of negative electrons on the outside of each molecule begin to repel (negative v negative). The molecules settle down to an equilibrium distance, where the attraction just balances the repulsion. Other substances are made of ions (these are completely charged atoms – positive and negative). Opposites ions attract and pull together strongly, but again, if they get too close, the negative clouds of electrons begin to repel and they settle down to a distance where the forces balance. I hope that is clear enough – it is a complex and advanced topic!! (Incidentally, try to avoid the word "reaction" unless you mean a chemical changes into a new substance). Kevin You may also find this site to be useful: http://library.thinkquest.org/10429/high/bonding/bonding.htm and this one: http://www.newi.ac.uk/buckleyc/bonding.htm Thanks for your question, Sue Scotino Mad Scientist Administration