When atoms join to make a molecule, their atomic orbitals merge together. The merging atomic areas form entirely new spaces called molecular orbitals. Some new orbitals hold the atoms tightly together and are called bonding orbitals.
Other new orbitals push the atoms apart and are called antibonding orbitals. Sometimes orbitals do not affect the bond at all and remain nonbonding. The number of new molecular orbitals always equals the number of starting atomic orbitals.
Electrons always fill the lowest energy molecular orbitals first before moving higher. This filling order helps chemists figure out if a molecule will be stable. It also shows exactly how strong the new molecular bonds will be.
This theory fixes several mistakes found in older chemical bonding rules. For example, it explains why some molecules act like weak magnets. It also helps us understand why certain chemical reactions happen easily.
Many students mistakenly think this theory completely replaces older bonding models. In reality, chemists use different models depending on the specific problem. Understanding these orbitals is crucial for designing new drugs and advanced materials.