Microchem
Microscale Chemistry Experimentation for Teachers

30. More modelling for explanation of NaCl synthesis

Energy is consumed to break the metallic bonds of solid sodium Na(s).
 

Energy is also needed for the ionisation of the sodium metals (Na).
The resulting positive sodium ions (Na⁺) have a smaller ionic radius than the Na atoms: The nucleus has to attract one electron less.

Bonding energy is to be supplied to transform chlorine molecules (Cl₂) into chlorine atoms (Cl)

Each electron which was donated by one Na atom during its ionisation is accepted by one chlorine atom (Cl).
During this step Cl atoms are transferred into negative chlorine ions (Cl^-).
While the radius of Na was decreasing during ionisation, the ionic radius of Cl is increasing during ionsisation.
The Cl^- ions have a bigger ionic radius than Na⁺ ions.