molecular biology. (mÉ-lÄk'yÉ-lÉr) The branch of biology that deals with the formation, structure, and function of macromolecules essential to life, such as nucleic acids and proteins, including their roles in cell replication and the transmission of genetic information.
Molecules containing more than two atoms are termed polyatomic molecules, e.g., carbon dioxide (CO2) and water (H2O). Polymer molecules may contain many thousands of component atoms. A water molecule is made up of two hydrogen atoms and one oxygen atom. A single oxygen atom contains six electrons in its outer shell, which can hold a total of eight electrons. When two hydrogen atoms are bound to an oxygen atom, the outer electron shell of oxygen is filled. EncyclopÃ¦dia Britannica, Inc.
Atoms have the  same number of protons and electrons, â¦ because otherwise, you would  have an ion.   A molecule consists of two or more atoms bonded together.    Atoms are single units of elements.   Molecules are agglomerations of two or more atoms  (of the same or different elements). A molecule is the smallest  particle of a chemical compound. Molecules are formed by atoms in a  multitude of different arrangements.   - Most atmospheric oxygen forms diatomic molecules (O2),  but also ozone (O3)   - One molecule of water has one atom of hydrogen and two atoms of  oxygen. So-called heavy water contains deuterium, which is hydrogen  that has neutrons.