Question

What is the chemical formula for magnesium bromide?

Answer 1

Hint: A chemical formula is the representation of the atoms present in any compound in their respective quantities. A chemical formula may be known as the molecular formula of the molecule as it tells the exact molecules. In a chemical formula, the cation is written first and then the anion.

Complete answer:
A chemical formula for any compound represents the exact quantities of atoms involved in that compound. While writing the chemical formula for any molecule, the cation is named and written before the anion of that molecule. The cation is the ion that carries the positive charge as it donates electrons, while anion carries the negative charge as it accepts electrons.
We have been given magnesium bromide. This compound consists of magnesium and bromine as the atoms. The magnesium ion is represented as, $M{{g}^{2+}}$, while the bromide ion is represented as, $B{{r}^{-}}$, this is because magnesium has 2 valence electrons so it has a charge of positive of 2 while bromine needs only 1 electron in valence shell to complete full configuration, and is more electronegative, so it has a negative charge of 1.
The chemical formulas of compounds are written in such a manner, as to compensate for the valencies or charges present in the atoms of the element. For instance, two positive charges containing ions cannot form a compound with an element having a charge of negative one. Therefore, those negative ions are taken in a quantity of two, as to compensate for the valence of the positive ions.
Here, magnesium have + 2 valence, as $M{{g}^{2+}}$, while bromide has a charge of -1 in $B{{r}^{-}}$ , so to balance the 2 positive charges of Mg, Br will be taken in amount of 2, thus the formula for magnesium bromide will be,
Magnesium bromide = $MgB{{r}_{2}}$
Hence, the chemical formula for magnesium bromide is $MgB{{r}_{2}}$.

Note:
When any atom is present in the form of anion, as it gains electrons, then its name is changed to ‘ide’ in the end. Therefore, bromine changes to bromide here. The valence of any element can be identified from its electronic configuration, as Mg has 2 valence electrons only, so it has a 2 valency, whereas bromine is more electronegative so the charge of Mg will be positive.