Question

Deduce the formulas of the following ionic compounds: (a) iron(lll) sulfide, (b) mercury(ll) nitrate, and (c) potassium sulfite.

Answer 1

For a: The chemical formula for Iron (III) sulfide is
`Fe_2S_3`

For b: The chemical formula for mercury (II) nitrate is
`Hg(NO_3)_2`

For c: The chemical formula for potassium sulfite is
`K_2SO_3`

Step-by-step explanation:

All the given compounds are ionic compounds. This means that between the atoms complete sharing of electrons takes place.

• For a:

Iron is the 26th element of periodic table having electronic configuration of
`[Ar]3d^64s^2`.

To form
`Fe^(3+)` ion, this element will loose 3 electrons.

Sulfur is the 16th element of periodic table having electronic configuration of
`[Ne]3s^23p^4`.

To form
`S^(2-)` ion, this element will gain 2 electrons.

By criss-cross method, the oxidation state of the ions gets exchanged and they form the subscripts of the other ions. This results in the formation of a neutral compound.

So, the chemical formula for Iron (III) sulfide is
`Fe_2S_3`

• For b:

Mercury is the 80th element of periodic table having electronic configuration of
`[Xe]4f^(14)5d^(10)6s^2`.

To form
`Hg^(2+)` ion, this element will loose 2 electrons.

Nitrate ion is a polyatomic ion having chemical formula of
`NO_3^(-)`

By criss-cross method, the oxidation state of the ions gets exchanged and they form the subscripts of the other ions. This results in the formation of a neutral compound.

So, the chemical formula for mercury (II) nitrate is
`Hg(NO_3)_2`

• For c:

Potassium is the 19th element of periodic table having electronic configuration of
`[Ar]4s^1`.

To form
`K^(+)` ion, this element will loose 1 electron.

Sulfite ion is a polyatomic ion having chemical formula of
`SO_3^(2-)`

By criss-cross method, the oxidation state of the ions gets exchanged and they form the subscripts of the other ions. This results in the formation of a neutral compound.

So, the chemical formula for potassium sulfite is
`K_2SO_3`