When an ionic bond forms, which part (s) of the atoms are directly involved?

The outermost electrons of the atom form ionic bonds.

There are three distinct parts of every atom, the protons, and neutrons that make the core of the atom and the electrons that orbit the core.

All atoms aim to achieve the configuration of their electron orbits like the ones found in noble gases such as helium.

The ionic bond is formed between ions, charged atoms, usually between a metal like sodium and a non-metal like chlorine.

A metal in an ionic bond donates an electron to achieve a stable configuration and the non-metal atoms accept an electron to their outer-most orbit to do the same. These atoms now become ions or charged atoms. Due to a loss of an electron, the metal now becomes positive, and the non-metal becomes negative due to the presence of an addition electron with a negative charge in its structure. This difference in charges attracts the two ions to each other and makes them form an ionic bond.