Tim Pope, age 11, of Pointe du Bois, Manitoba, Canada, for his question:
How does a molecular substance stay together?
This realm of miniature particles uses the same adhesive to attach electrons to atoms, to package atoms into molecules and to build molecules into chemical compounds. It is invisible electrical energy, not at all like the tacky glues we use to paste pages in scrap books and stick on band aids. It works because certain atomic particles bear equal electrical charges. Electrons have negative charges; protons have opposite positive charges.
The invisible adhesive that holds certain molecules together provides a basic key in solving many problems in chemistry. It is a built in property of the protons in the atomic nucleus and the electrons that swarm around it. Their plus and minus electrical charges resemble the opposite poles of two magnets. The positive protons and negative electrons attract each other and tend to cling together. A normal atom has an equal number of each. Then charges cancel out and the atom is electrically neutral.
However, atoms try to arrange their swarming electrons in orderly shells. The inner shell is complete with two electrons, the second shell with eight, and the third with 16. When the outer shell is incomplete, different atoms make various arrangements to assist each other. For example, hydrogen has one lone electron, and oxygen needs two to complete its outer shell. In a molecule of water, one oxygen atom completes it outer shell by sharing the lone electron of two hydrogen atoms. Together the three atoms have 10 protons and 10 electrons. The water molecule should be electrically balanced and neutral, with no extra plus or minus charges to attract other watex:~ molecules.
However, the oxygen nucleus with eight protons is much stronger than the two hydrogen atoms, with one proton apiece. For this reason, the swarming electrons favor the oxygen end of the molecule. They give it a slight negative charge and leave the hydrogen end with a slight positive charge. And these plus and minus zones attract the opposite ends of other water molecules. Groups of four to eight link end to opposite end and form chains. This rather loose electrical bondage makes water molecules cling together, while playing games of follow the leader.
Other atoms form molecules by transferring electrons to adjust their outer shells. For example, sodium has only one electron in its outer shell and chlorine needs one
more to complete its outer shell. When these two atoms form a molecule, the sodium transfers its one outer electron. However, this upsets the neutral balance of both atoms. The sodium loses a minus charge and becomes a positive ion. The chlorine becomes a negative ion. The molecule inherits these opposite ion charges which attract opposite charges in sister molecules. Zillions of them cling together and build a crystal of sodium chloride alias table salt.
Temperature, the structure of particles, and other factors modify the behavior of molecules. But in material substances they are held together mainly by the mutual attraction between charges of positive and negative electricity. In the world at large, we are familiar with the negative electricity of gad about electrons. But positive electricity is tightly locked with the protons in the nuclei of tiny atoms.