Post Closed as "unclear what you're asking" by Mithoron, andselisk, airhuff, paracetamol, M.A.R.
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Ions and Polyatomic Ions

Before a sodium atom and a chlorine atom combine together to form the ionic compound $NaCl$, they are just neutral atoms. However, when an electron is transferred from the outer energy level of the sodium atom to the chlorine atom, both of these gain a charge on them; the sodium atom or ion has a charge of $1+$ and the chlorine ion has a charge of $1-$. Both of these ions attract each other and an ionic bond is formed between them.

But what happens when an atom of an element say $Ca$ combines with a polyatomic ion say $OH^-$. Is this calcium atom an ion, is it already a charged atom when it interacts with the hydroxide ion or does it gain the charge by any transfer of electrons to the $OH^-$ ion and becomes $Ca^{2+}$ to bond with the $OH^-$ ion?

I think the polyatomic ions say $OH^-$ is already an ion and not an uncharged compound of elements that gains charge as in the case of $NaCl$, and the bond between an ion and a polyatomic ion is due to the attractive forces between them if already they have opposite charges.