As two atoms approach each other to form a chemical bond, what primarily causes the electron density between them to change?

• A. The emission of photons from the atoms
• B. The decrease in the number of protons in the nuclei
• C. The increase in atomic mass of the atoms
• D. The overlap of atomic orbitals leading to the formation of molecular orbitals

Answer: (D)

Verified step by step guidance

1. Understand that when two atoms approach each other to form a chemical bond, their atomic orbitals begin to interact.
2. Recognize that atomic orbitals are regions around an atom where electrons are likely to be found, and when atoms come close, these orbitals can overlap.
3. The overlap of atomic orbitals allows electrons to be shared or redistributed between the atoms, which changes the electron density between them.
4. This overlap leads to the formation of molecular orbitals, which are new orbitals that belong to the entire molecule rather than individual atoms.
5. Therefore, the primary cause of the change in electron density between two approaching atoms is the overlap of atomic orbitals forming molecular orbitals, not changes in protons, atomic mass, or photon emission.