Question

What is the difference between 2H and ${H_2}$?

Answer 1

Hint : In order to answer this question, you must be aware about the concept of chemical bonding and molecular structure. Chemical bonding is defined as the formation of bonds between atoms, molecules, ions etc. Molecular structure describes the location of the atoms, and not the electrons.

Complete Step By Step Answer:
${H_2}$ stands for molecular hydrogen. It is formed when two hydrogen atoms combine. It is held together by a single bond, also known as a sigma bond. ${H_2}$ has two atoms sharing their electrons for completing their duplet. Hydrogen is commonly used in hydrocracking to create petroleum products, including gasoline and diesel. It is also used to remove contaminants like sulphur and to create methanol.
 2H stands for two moles of elemental hydrogen. It should be noted that elemental hydrogen has no bonds. These are two distinct hydrogen atoms that are not joined together as a unit.
However, ${H_2}$ molecule is more stable than the 2H atom but 2H has higher entropy. Entropy is a measure of randomness or disorderness. 2H has more randomness because the elemental hydrogen has no bonds and are distinct.
Therefore, ${H_2}$ is one molecule of hydrogen gas, whereas 2H is two atoms of hydrogen.

Note :
 ${H_2}$ is a flammable, colorless, odourless gas that can act as a reducing agent under certain circumstances. It was previously considered physiologically inert in mammalian cells, and was not thought to react with active substrates in biological systems.