Final answer:
When two or more equivalent dot structures exist for a molecule, these are known as resonance structures. These structures represent different distributions of electrons while the arrangement of atoms remains constant, and the actual structure of the molecule is a resonance hybrid, which is an average of all possible resonance forms.
Step-by-step explanation:
When two or more equivalent dot structures can be written for a given molecule, it is said to have resonance structures. Resonance forms are different Lewis structures that have the same arrangement of atoms but different arrangements of electrons for a given molecule. A resonance hybrid is considered an average of the resonance forms shown by the individual structures. For example, a molecule like ozone (O3) can be represented with different resonance structures where the position of the atoms stays the same, but the position of the electrons varies. These structures are connected with double-headed arrows, symbolizing that the true structure is an average of these resonance forms.A single bond in resonance structures represents a bond in which a single pair of electrons is shared between two atoms. The true nature of the bonding in a resonance hybrid often involves fractional bond orders instead of simple integers. For example, each carbon-oxygen bond in the carbonate ion has a bond-order of approximately 1.33, which means each bond is somewhere between a single and a double bond.It is important to distinguish between resonance and other concepts such as isomers (molecules with the same molecular formula but different structures), hybrid (blending of atomic orbitals in the formation of new orbitals suitable for the pairing of electrons), and polar (a type of chemical bond where a pair of electrons is unequally shared between two atoms).