A computer rendering of the Nitrogen Molecule, which is a diatomic molecule.

Diatomic molecules are molecules formed of two atoms, of the same or different chemical elements. The prefix di- means two in Greek. Diatomic elements are those that almost exclusively exist as diatomic molecules, known as homonuclear diatomic molecules in their natural elemental state when they are not chemically bonded with other elements. Examples include H₂ and O₂. Earth's atmosphere is composed almost completely (99%) of diatomic molecules which are oxygen (O₂) (21%) and nitrogen (N₂) (78%). The remaining 1% is predominantly argon (0.9340%) Image File history File links Nitrogen_-Molecular-.JPG Summary Licensing I, the creator of this work, hereby release it into the public domain. ... Image File history File links Nitrogen_-Molecular-.JPG Summary Licensing I, the creator of this work, hereby release it into the public domain. ... Properties In chemistry and physics, an atom (Greek ἄτομος or átomos meaning indivisible) is the smallest particle of a chemical element that retains its chemical properties. ... The periodic table of the chemical elements A chemical element, often called simply an element, is a substance that cannot be decomposed or transformed into other chemical substances by ordinary chemical processes. ... A chemical bond is the physical phenomenon (or phenomena) responsible for the attractive interactions betwen atoms that confers stability to di- and polyatomic chemical compounds. ... Layers of Atmosphere (NOAA) Air redirects here. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless Atomic mass 14. ... General Name, Symbol, Number argon, Ar, 18 Chemical series noble gases Group, Period, Block 18, 3, p Appearance colorless Atomic mass 39. ...

Oxygen also exists as the triatomic molecule ozone (O₃). For other uses, see Ozone (disambiguation). ...

The diatomic elements are hydrogen, nitrogen, oxygen, and the halogens: fluorine, chlorine, bromine, iodine, and astatine. Astatine is so rare in nature (its most stable isotope has a half-life of only 8.1 hours) that it is usually not considered. Many metals are also diatomic when in their gaseous states. General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless Atomic mass 14. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ... The halogens exist as diatomic molecules in the gas, liquid and solid phases. ... General Name, Symbol, Number fluorine, F, 9 Chemical series halogens Group, Period, Block 17, 2, p Appearance Yellowish brown gas Atomic mass 18. ... General Name, Symbol, Number chlorine, Cl, 17 Chemical series halogens Group, Period, Block 17, 3, p Appearance yellowish green Atomic mass 35. ... General Name, Symbol, Number bromine, Br, 35 Chemical series halogens Group, Period, Block 17, 4, p Appearance gas/liquid: red-brown solid: metallic luster Atomic mass 79. ... General Name, Symbol, Number iodine, I, 53 Chemical series halogens Group, Period, Block 17, 5, p Appearance violet-dark gray, lustrous Atomic mass 126. ... General Name, Symbol, Number astatine, At, 85 Chemical series halogens Group, Period, Block 17, 6, p Appearance metallic (presumed) Atomic mass (210) g/mol Electron configuration [Xe] 4f14 5d10 6s2 6p5 Electrons per shell 2, 8, 18, 32, 18, 7 Physical properties Phase solid Melting point 575 K (302 Â°C... Isotopes are any of the several different forms of an element each having different atomic mass. ... Half-Life For a quantity subject to exponential decay, the half-life is the time required for the quantity to fall to half of its initial value. ...

The bond in a homonuclear diatomic molecule is non polar and fully covalent. Examples of heteronuclear diatomic molecules include carbon monoxide (CO) and nitric oxide (NO). This article does not cite its references or sources. ... Carbon monoxide, with the chemical formula CO, is a colourless, odourless and tasteless gas. ... The chemical compound nitric oxide is a gas with chemical formula NO. It is an important signaling molecule in the body of mammals including humans, one of the few gaseous signaling molecules known. ...

Other elements exist which form diatomic molecules but with high instability and reactivity. An example is diphosphorus. Diphosphorus or P2 is the diatomic form of phosphorus. ...

Energy levels

A common, approximate, model of a diatomic molecule is that of a dumbbell - that is, each atom is on one end of a spring or rod.

Now this dumbbell molecule can only move in a few specific ways:

• It can vibrate such that the atoms oscillate between getting closer and farther from each other.
• It can rotate or spin about some axis.

Rotational

Classically, the kinetic energy of rotation is Kinetic energy is the energy that a body possesses as a result of its motion. ...

where

is the angular momentum

is the moment of inertia of the molecule

Now, for quantum systems like a molecule, angular momentum can only have specific descrete levels. So, angular momentum is given by Gyroscope. ... Moment of inertia, also called mass moment of inertia and, sometimes, the angular mass, (SI units kg m², English units lbs ft2) quantifies the rotational inertia of a rigid body, i. ...

where l is some positive integer and is Plank's constant.

Also, the moment of inertia of this molecule is A commemoration plaque for Max Planck on his discovery of Plancks constant, in front of Humboldt University, Berlin Plancks constant, denoted h, is a physical constant that is used to describe the sizes of quanta. ...

where

is the reduced mass of the molecule and

is the average distance between the two atoms in the molecule.

So, plugging in the angular momentum and moment of inertia, the rotational energy levels of a diatomic molecule are given by: Reduced mass is a concept that allows one to solve the two-body problem of mechanics as if it were a one body problem. ...

Vibrational

The other way a diatomic molecule can move is to have to have each atom oscillate - or vibrate - along a line connecting them. Look up vibration in Wiktionary, the free dictionary. ...

The energy of this vibration is exactly the same as a quantum harmonic oscillator: The quantum harmonic oscillator is the quantum mechanical analogue of the classical harmonic oscillator. ...

where

n is some integer

h is Plank's constant and

f is the frequency of the vibration.

A commemoration plaque for Max Planck on his discovery of Plancks constant, in front of Humboldt University, Berlin Plancks constant, denoted h, is a physical constant that is used to describe the sizes of quanta. ... Sine waves of various frequencies; the bottom waves have higher frequencies than those above. ...

Comparison between rotation and vibration

The lowest rotational energy level is when l = 0. The next highest energy level (l = 1) of O₂, has an energy of roughly:

Thus, transitions between rotational energy levels yield photons in the microwave region. The word light is defined here as electromagnetic radiation of any wavelength; thus, X-rays, gamma rays, ultraviolet light, microwaves, radio waves, and visible light are all forms of light. ... Microwaves are electromagnetic waves with wavelengths longer than those of terahertz (THz) wavelengths, but relatively short for radio waves. ...

The lowest vibrational energy level is when n = 0, and a typical vibration frequency is 5x10¹³ Hz. So, doing a similar calculation as with above gives:

.

So a typical transition between vibrational energy levels is about 100 times greater than a typical transition between rotational energy levels.

See also

• Fonclbrishp

This is an easy way to remember all the diatomic elements, all at once. ...

References

• Hyperphysics - Rotational Spectra of Rigid Rotor Molecules
• Hyperphysics - Quantum Harmonic Oscillator
• Tipler, Paul (1998). Physics For Scientists and Engineers : Vol. 1 (4th ed.). W. H. Freeman. ISBN 1-57259-491-8.