The reason why bonded atoms or molecules have lower energy than separate atoms is primarily due to the formation of chemical bonds, which involve the sharing, transfer, or redistribution of electrons between atoms.
When atoms come together to form a bond, their valence electrons interact and occupy regions of space between the nuclei. This results in a more stable configuration and lower potential energy compared to the separate atoms.
There are several ways in which chemical bonds can be formed:
Covalent Bonds: In covalent bonding, atoms share electrons to achieve a more stable electron configuration. This sharing of electrons allows each atom to fill its outer electron shell and attain a more favorable electronic configuration, leading to decreased energy.
Ionic Bonds: Ionic bonding involves the transfer of electrons from one atom to another. This transfer results in the formation of positively charged ions (cation) and negatively charged ions (anion), which are attracted to each other by electrostatic forces. The resulting ionic compound has lower energy compared to the separate atoms due to the attractive forces between the oppositely charged ions.
Metallic Bonds: In metallic bonding, valence electrons are delocalized and free to move throughout a lattice of positively charged metal ions. This "sea" of electrons holds the metal ions together, resulting in lower energy compared to separate metal atoms.
Overall, the formation of chemical bonds allows atoms to achieve a more stable electron configuration, which corresponds to a lower energy state. The energy required for the transfer of valence electrons can vary depending on the type of bonding involved, but the end result is a more energetically favorable arrangement of atoms.