Mole ratios
Reactants and products
Type of reaction eg equilibrium
Enthalpy
Charges of ions
You should read up on Proust's law, better known as the Law of Definite Proportions. This is a chemical law that defines your question more generally, on why the ratio of elements and ions are always fixed.
Basically, this compound Magnesium(II) Chloride is MgCl2 because it has the same number of protons, neutrons, and electrons all the way. This defines the properties of the compound or atom.
The simple machine used is called atwood machine.
Lewis Structure is drawn in following steps,
1) Calculate Number of Valence Electrons: # of Valence electrons in Mg = 2
# of Valence electrons in I = 7
# of Valence electrons in I = 7
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Total Valence electrons = 16
2) Draw Mg as a central atom surround it by two atoms of Iodine.3) Connect each Iodine atom to Mg, and subtract two electrons per bond. In this case we will subtract 4 electrons from total valence electrons. i.e.
Total Valence electrons 16
- Four electrons - 4
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12
4) Now start adding the remaining 12 electrons on more electronegative atoms i.e. Iodine.
The final lewis structure formed is as follow,