#### CHAPTER 12 ATOMS

Radius of orbit of electron is given by

$\mathrm{r}=\frac{4\mathrm{\pi }{\mathrm{\epsilon }}_{0}{\mathrm{n}}^{2}{\mathrm{h}}^{2}}{4{\mathrm{\pi }}^{2}\mathrm{m}\mathrm{Z}{\mathrm{e}}^{2}}=\frac{{\mathrm{\epsilon }}_{0}{\mathrm{n}}^{2}{\mathrm{h}}^{2}}{\mathrm{\pi }\mathrm{m}\mathrm{Z}{\mathrm{e}}^{2}}$

where,

n = principle quantum number,

h = Planck’s constant,

m = mass of an electron,

Z = atomic number and

e = electronic charge.

Substituting the values of h, m, εo and e , we get,

r1 = 5.29 × 10–11 m.
This is called the Bohr radius, and is represented by ao.