Most elements are found as single atoms. For example, iron exists as single atoms of iron (Fe), and sulfur exists as single atoms of sulfur (S). Some elements do not exist naturally as single atoms. They chemically combine with another atom of that same element to form “diatomic” ( 2 atoms) molecules. A molecule of an element has just one type of atom. The seven diatomic elements are hydrogen, oxygen, nitrogen, chlorine, bromine, iodine, and fluorine. One molecule of oxygen has 2 atoms of oxygen (O₂) that are chemically joined, and one molecule of hydrogen contains 2 atoms of hydrogen (H₂) that are chemically joined.Remember there are three phases that matter occurs in: liquid, gas, and solid. In solids, molecules are packed together tightly. They can (and do) move around, but not as much as they do in liquids. In liquids, molecules can slide around easily and pass each other. In gases, molecules are spread out and move very easily from one area to another.
