A hydrogen molecule forms from two hydrogen atoms, each with one electron in a 1 s orbital. The two hydrogen atoms are attracted to the same pair of electrons in the covalent bond. The bond is represented either as a pair of “dots” or as a solid line. Each hydrogen atom acquires a helium-like electron configuration. Shared electrons located in the space between the two nuclei are called bonding electrons. The bonded pair is the “glue” that holds the atoms together in molecular units. The hydrogen molecule is the simplest substance having a covalent bond.
The lack of a number preceding the carbon symbol C and the compound formula CO2 shows that there is one carbon atom and one carbon dioxide molecule. Subscript numbers in chemical formulas represent the number of atoms or molecules immediately preceding the subscript.
The change in energy level is equivalent to the energy of the released photon. This is related by Planck's equation: E = hcf The higher the energy change, the greater the frequency, f, of the photon.
