Why does bracket comes in ca (oh)2but not in mgcl2??
Answers
AS-SALAMU-ALYKUM
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Because in Ca(OH)2 this is whole 2 which means it is with both O and H that is both H and O has two atoms .
And ....
In MgCl2 this 2 is just with chlorine that is it has two atoms
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INSHALLAH it will help U
OH is a polyatomic ion. These are just clusters of atoms that act as a single entity carry a charge, so if they don't come together they're just simply random atoms. Hence these always occur as a group.
In Ca(OH)2 which is calcium hydroxide, one calcium atom (in this case ion) combines with 2 OH ions. Since OH is a polyatomic ion, O and H always occur together, hence to show that this single entity of one O and H, the ion is enclosed in brackets.
If the formula was written like this CaOH2, It means that only H occurs twice and not along with O as a polyatomic ion as it is supposed to be. This changes the formula entirely and we would end up with a random compound that is completely different from calcium hydroxide.
In MgCl2 which is magnesium chloride, the formula shows that the chlorine ion (which is a charged atom of the element chlorine) occurs twice. Keep in mind that Cl is an ion of an element, and not a polyatomic ion.
I hope you find this useful.