Question

The chemical formula of a compound does not represent:
A. The total number of atoms in a molecule of the compound
B. the number of various atoms in 1 molecule of the compound
C. the state of the molecules of the compound
D. the composition of the molecules of the compound

Answer 1

Hint: The chemical formula of a compound represents the number of atoms present in the compound and it is formed by satisfying the valencies of all the atoms present in the compound. It tells us all the atoms present in the compound and also the ratio of the atoms in that compound.

Complete step by step solution:
-Valency is the number of the electrons present in the outermost shell of an atom which is also called the valence shell of an atom. Those electrons are important to be studied as they are the most loosely held electrons of the atoms.
-Now, we know that every atom tries to reach the electronic configuration of the noble gases to become stable like them. The configuration of noble gases is of the form $n{{s}^{2}}n{{p}^{6}}$ .
-This configuration is reached either by sharing of electrons or losing of electrons. The chemical formula is found by the criss-cross method. We should know the valencies of the element in order to write the chemical formula for the compounds of that element.
-Let us take an example of Mg. It has 2 valence electrons. If it is made to react with the anions like nitrate, sulfate and phosphate, it will form products with different chemical formulas. Eg.

\[Mg+S{{O}_{4}}\to MgS{{O}_{4}}\]
\[Mg+2N{{O}_{3}}\to Mg{{\left( N{{O}_{3}} \right)}_{2}}\]
\[3Mg+2P{{O}_{4}}\to M{{g}_{3}}{{\left( P{{O}_{4}} \right)}_{2}}\]
-The valencies are the same in the first reaction. So the formula is simple. In the second reaction, Mg has valency 2 and nitrate has valency 1. So they appear in criss-cross manner as the number of atoms needed to react to form the compound. In the third reaction, phosphate has valency 3 and so reaction occurs as stated above.
-So we see that the chemical formula gives us the information about the total number of atoms in a molecule of the compound, the number of various atoms in 1 molecule of the compound, composition of the molecules of the compound but not about the state of the molecules of the compound.

Therefore the correct option is C.

Note: The chemical formula is very important as without knowing it, we cannot write the balanced chemical equation. It need not be learnt for every compound as there are millions of compounds. We can just find it by the criss-cross method as shown above. We only need to know the valency of the atoms and the total charges present on the radicals that react with the elements.