The crisscross method for writing ionic formulas implies that the charge of one ion becomes the subscript of the second ion, and vice versa.
In addition to this, you need to look out for a common factor that the two subscripts would have, and use it to write them in the lowest possible whole ratio.
For example, if you have an
So, you want to write the ionic formula for magnesium oxide. The first thing you need to do is identify the cation, anion, and their respective charges.
On the other hand, oxygen, being located in group 16, will gain two electrons to form the
Using the crisscross method will get you
Notice that you can simplify the two subscripts by 2 to get the smallest possible whole ratio of
Crisscross method is simply writing the charges crossly near each element.
Since oxidation number of Mg (metal) is +2 and oxygen (nonmetal) is -2, if we cross them and write next to each; we get
Note that, in chemistry it is always preferred to write the simplest form of the formulas. By dividing each number of elements by 2, we get
crisscross method is a method for determining formula of compound with the help of charges.
here , charge carried by magnesium = +2(since its a metal)
charge carried by oxygen= -2(since its a nonmetal) Mg+2O-2
on crisscrossing the values we get
since both the charges get cancels out = -2+2= 0
therefore formula is MgO