Lewis structure is drawn in following steps,
1) Calculate the total number of electrons in valence shell of all elements,
Ca = 2
Cl = 7
Cl = 7
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Total valence electrons = 16
2) Draw central atom (Ca) in center surrounded by remaining elements (Cl) and draw a single bond between central atom and surrounding atoms. Subtract 2 electrons per bond from total valence electrons. And divide the remaining electrons on the most electronegative element. The structure will be as shown below,
Result:
So it required 16 electrons to draw the Lewis Structure of CaCl₂
