The particle diagram will show magnesium atoms represented as circles with a positive charge (Mg²⁺) and hydrochloric acid molecules represented as circles with a negative charge (Clˉ). The magnesium atoms will be surrounded by a sea of electrons.

After the reaction:

The particle diagram will show magnesium chloride molecules, which are composed of one magnesium atom and two chloride atoms. The magnesium atoms will have lost two electrons to the chloride atoms, resulting in a positive charge for the magnesium atom and a negative charge for each chloride atom. The magnesium chloride molecules will be surrounded by a sea of electrons.

Overall, the reaction between magnesium and hydrochloric acid results in the formation of magnesium chloride and hydrogen gas.