Science, Tech, Math › Science Diatomic Molecules Homonuclear and Heteronuclear Share Flipboard Email Print Covalent Chemical Bond. PASIEKA/Getty Images Science Chemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated February 08, 2018 There are hundreds of diatomic molecules. This list includes diatomic elements and diatomic chemical compounds. Mononuclear Diatomic Molecules Some of these molecules consist of one element or are diatomic elements. Diatomic elements are examples of homonuclear molecules, where all of the atoms in the molecule are the same. The chemical bonds between the atoms are covalent and nonpolar. The seven diatomic elements are: Hydrogen (H2)Nitrogen (N2)Oxygen (O2)Fluorine (F2)Chlorine (Cl2)Iodine (I2)Bromine (Br2) 5 or 7 Diatomic Elements? Some sources will say there are five diatomic elements, rather than seven. This is because only five elements form stable diatomic molecules at standard temperature and pressure: the gases hydrogen, nitrogen, oxygen, fluorine, and chlorine. Bromine and iodine form homonuclear diatomic molecules at slightly higher temperatures. It's possible that an eighth element forms a diatomic molecule. The status of astatine is unknown. Heteronuclear Diatomic Molecules Many other diatomic molecules consist of two elements. In fact, most elements form diatomic molecules, particularly at higher temperatures. Past a certain temperature, however, all molecules break into their constituent atoms. The noble gases do not form diatomic molecules. Diatomic molecules consisting of two different elements are called heteronuclear molecules. Here are some heteronuclear diatomic molecules: CONOMgOHClKBrHFSiO Binary Compounds Are Not Always Considered Diatomic There are many binary compounds consisting of a 1-to-1 ratio of two types of atoms, yet they are not always considered to be diatomic molecules. The reason is that these compounds are only gaseous diatomic molecules when they are evaporated. When they cool to room temperature, the molecules form polymers. Examples of this type of compound include silicon oxide (SiO) and magnesium oxide (MgO). Diatomic Molecule Geometry All diatomic molecules have linear geometry. There isn't any other possible geometry because connecting a pair of objects necessarily produces a line. Linear geometry is the simplest arrangement of atoms in a molecule. Other Diatomic Elements It's possible for additional elements to form homonuclear diatomic molecules. These elements are diatomic when evaporated, yet polymerize when they are cooled. Elemental phosphorus can be heated to yield diphosphorus, P2. Sulfur vapor primarily consists of disulfur, S2. Lithium forms dilithium, Li2, in the gas phase (and no, you can't run a starship on it). Unusual diatomic elements include ditungsten (W2) and dimolybdenum (Mo2), which are joined via sextuple bonds as gasses. Fun Fact About Diatomic Elements Did you realize around 99 percent of the Earth's atmosphere consists of just two diatomic molecules? Nitrogen accounts for 78 percent of the atmosphere, while oxygen is 21 percent. The most abundant molecule in the universe is also a diatomic element. Hydrogen, H2, accounts for much of the mass of the universe, although it only accounts for one part per million concentration in Earth's atmosphere.