When a person steps on something sharp (like a nail), the leg that is stepping on the nail reflexively pulls away (the flexor muscles contract and the extensor muscles relax), while the other leg reflexively takes the weight of the whole body (the flexor muscles relax and the extensor muscles contract) in preparation for the jerk.
A molecule is the smallest particle of a substance that exists independently. Molecules of most elements are made up of only one of atom of that element. Oxygen, along with nitrogen, hydrogen, and chlorine are made up of two atoms. Look at the model of oxygen above. The two balls represents the two oxygen molecules.
The smallest particle or piece of a compound is called a molecule. It is the basic unit of a substance and carries basically all of a compound's chemical properties. It cannot â¦ be further reduced and still retain the compound's chemical identity.  An easy example is water. Physical Properties of Chemicals Chemistry is the study of chemical properties and reactions. 2  Every chemical has a set of properties that distinguishes it from other chemicals and makes it unique.