Oxygen is sometimes represented as O and sometimes as O₂. What is the difference between these symbols?
The symbol O represents a single oxygen atom. An oxygen atom has six electrons in its valence shell and requires two more electrons to complete its octet.
The symbol O₂ represents an oxygen molecule. It is formed when two oxygen atoms share two electrons each to complete their octets. In this molecule, the two atoms are joined by two pairs of shared electrons, meaning they are held together by a double bond (O=O).
Explanation
The question differentiates between an atom and a molecule of oxygen. The context explains that 'O' is the atom with 6 valence electrons needing 2 more, while 'O₂' is the molecule formed when two such atoms share two electrons each, resulting in a double bond.