Question

Using criss-cross method, write down the chemical formulae of (1) Potassium oxide (ii) Aluminium nitride (iii) Sodium hydroxide​

Answer 1

Answer:

Let’s us discuss about the given compound as,

A.Magnesium chloride

We have to remember that the atomic number of Magnesium is 12 and has a valency of 2. It means it has two electrons in the outermost shell for bonding. The atomic number of chlorine is 17 and has 7 electrons in the outermost shell. It means it just needs one more atom for bonding. Hence, we will use atoms of chlorine to bond with one atom of magnesium.

We can apply the criss-cross method for this compound as,

Therefore, the chemical formula of magnesium chloride is MgCl2.

B.Calcium oxide

We have to know that the atomic number of calcium 20 and has a valency of 2, it means it has 2 two atoms in the outermost shell for bonding. The atomic number of Oxygen is 8 and has a valency of 2, it has 6 atoms in the outermost shell, it needs more 2 to complete the octet. Hence, we need one calcium atom to bond with one oxygen atom.

We can apply the criss-cross method for this compound as,

Therefore, the chemical formula of magnesium chloride is CaO.

C.Copper nitrate

We have to know that the atomic number of copper is 29 and has two atoms in the outermost shell for bonding. While a nitrate molecule has only one valence electron. We need 2 nitrate molecules to satisfy the valency of 1 copper atom.

We can apply the criss-cross method for this compound as,

Therefore, the chemical formula of magnesium chloride is Cu(NO3)2.

D.Aluminium chloride

We have to know that the atomic number of aluminium is 13 and has a valency of 3 atoms and chlorine atom has a valency of 1. Since it has 7 electrons in the outermost shell. Thus, we need 3 chlorine atoms to satisfy the valency of 1 aluminium atom.

We can apply the criss-cross method for this compound as,

Therefore, the chemical formula of magnesium chloride is AlCl3.

E.Potassium nitrate

We have to remember that the atomic number of potassium is 19 and has a valency of 1 and nitrate also has a valency of 1, since it needs one more atom to complete its octet. Hence, we need only one molecule of nitrate for one atom of potassium.

We can apply the criss-cross method for this compound as,