Everything about Diatomic Molecule totally explained
Diatomic molecules are molecules made only of two
atoms, of either the same or different
chemical elements. The prefix di- means two in Greek.
Description and occurrence in nature
Huber and
Herzberg's book,
Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules, lists hundreds of diatomic molecules, some which have been detected spectroscopically in
interstellar space. However, few diatomics are found to occur naturally on Earth outside of laboratories. About 99% of the
Earth's atmosphere is composed of diatomic molecules, specifically
oxygen O2 (21%) and
nitrogen N2 (78%), with the remaining 1% being mostly
argon (0.9340%). The natural abundance of
hydrogen (H2) in the Earth's atmosphere is only on the order of parts per million, but H
2 is, in fact, the most abundant molecule seen in nature, dominating the composition of stars.
Elements that consist of diatomic molecules, under typical laboratory conditions of 1 bar and 25
oC, include
hydrogen (H2),
nitrogen (N2),
oxygen (O2), and the
halogens:
fluorine (F2),
chlorine (Cl2),
bromine (Br2),
iodine (I2), and, perhaps,
astatine (At2). Again note that many other diatomics are possible, such as metals heated to their gaseous states. Also, many diatomic molecules are unstable and highly reactive, such as
diphosphorus. Many
compounds are made of diatomic molecules, including CO and HBr.
If a diatomic molecule consists of two atoms of the same element, such as H
2 and O
2, then it's said to be
homonuclear, but otherwise it's said to
heteronuclear, such as with CO or NO. The bond in a homonuclear diatomic molecule is non-polar and fully
covalent.
Molecular Geometry
The diatomic molecule
molecular geometry is the simplest
spatial arrangement of atoms.. This configuration is more commonly referred to in the
VSEPR theory as the AX1E* . Unlike other systems in VSEPR, there's no central atom.
Energy levels
It is convenient, and common, to represent a diatomic molecule as two point masses (the two atoms) connected by a massless spring. The energies involved in the various motions of the molecule can then be broken down into three categories.
- The translational energies
- The rotational energies
- The vibrational energies
Translational energies
The translational energy of the molecule is simply given by the kinetic energy expression:
» .
So the spacing, and the energy of a typical spectroscopic transition, between
vibrational energy levels is about 100 times greater than that of a typical transition between
rotational energy levels.
Further Information
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