Question

In the HCl molecule, the separation between the nuclei of the two atoms is about 1.27 Å (1 Å = 10^–10 m). Find the approximate location of the CM of the molecule, given that a chlorine atom is about 35.5 times as massive as a hydrogen atom and nearly all the mass of an atom is concentrated in its nucleus.

Answer 1

The given situation can be shown as:

Mass of H atom = m
Mass of Cl atom = 35.5m
Let thecentre of mass of the system lie at a distance x from the Cl atom.
Distance of the centre of mass from the H atom = (1.27 – x)
Let us assume that thecentre of mass of the given molecule lies at the origin. Therefore, 

we can have:

Here, the negative sign indicates that the centre of mass lies at the left of the molecule.
Hence, thecentre of mass of the HCl molecule lies 0.037Å from the Cl atom.