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In any chemical reaction, identifying the reactants is a crucial first step. Reactants are the starting materials that undergo a chemical change to form products. For the formation of magnesium chloride (\text{MgCl}_2\text{MgCl}\(_{2}\)), the key reactants are:

• Magnesium (Mg)
• Chlorine (\text{Cl}_2\text{Cl}\(_{2}\))

Magnesium is a shiny, silvery-white metal with the atomic number 12, found in Group 2 of the periodic table. Chlorine, on the other hand, is a greenish-yellow gas, found in Group 17 of the periodic table. When magnesium and chlorine react, they form the compound magnesium chloride through a series of steps involving electron transfer and ionic bond formation.

Understanding the electron configuration of atoms helps explain their chemical behavior.
Magnesium has the electron configuration \text{[Ne]3s^2}\text{[Ne]}3s\(^{2}\), indicating it has two electrons in its outermost shell. These are the electrons involved in chemical reactions.
Chlorine has the electron configuration \text{[Ne]3s^2 3p^5}\text{[Ne]}3s\(^{2}\) 3p\({^5}\), meaning it has seven electrons in its outermost shell and needs one more electron to achieve a stable configuration of eight electrons, similar to the noble gases.
In a chemical reaction, electron configuration changes as atoms seek stability, usually by gaining or losing electrons. For example, in the formation of magnesium chloride, magnesium loses its two outermost electrons:

Ionic bond formation occurs when atoms transfer electrons to achieve stable electron configurations.
Magnesium, with two electrons in its outer shell, will lose these electrons to form a stable \text{Mg}^{2+}\text{Mg}\(^{2+}\) ion.
Chlorine, needing one electron to complete its outer shell, will gain an electron to form \text{Cl}^-\text{Cl}\(^{-}\) ions. Each chlorine molecule (\text{Cl}_2\text{Cl}\(_{2}\)) produces two \text{Cl}^-\text{Cl}\(^{-}\) ions.
The reaction can be summed up as: \text{Mg} + \text{Cl}_2 \rightarrow \text{MgCl}_2\text{Mg} + \text{Cl}\(_{2}\) \rightarrow \text{MgCl}\(_{2}\).
This process results in the formation of ionic bonds due to the strong electrostatic attraction between the \text{Mg}^{2+}\text{Mg}\(^{2+}\) cations and the \text{Cl}^-\text{Cl}\(^{-}\) anions, giving rise to a stable ionic compound, magnesium chloride (\text{MgCl}_2\text{MgCl}\(_{2}\)).