# AP Inter 2nd Year Physics Notes Chapter 13 Atoms

Students can go through AP Inter 2nd Year Physics Notes 13th Lesson Atoms will help students in revising the entire concepts quickly.

## AP Inter 2nd Year Physics Notes 13th Lesson Atoms

→ J-J-Thomson proposed a structure for the atom.

→ Rutherford and then Niel Bohr modified the structure of atom proposed by Thomson.

→ Rutherford α – particle scattering experiment established the existence of nucleus.

→ The distance of closest approach, gives an estimate of the size of the nucleus.

→ Rutherford’s atom model could not explain the stability of the atom and the line spectrum of atoms.

→ Bohr suggested a new model of atoms to account for the stability of the atom and emission of line spectra by the atoms.

→ Bohr postulated that the electrons can revolve only in certain non-radiating orbits for which mvr = $$\frac{\mathrm{nh}}{2 \pi}$$

→ Non-radiating orbits are called stationary orbits.

→ Stationary orbits of electrons are not equally spaced.

→ The radius of first orbit of hydrogen atom is called Bohr’s radius.

→ The total energy of an electron in an orbit is equal to the negative of the K.E in that orbit.

→ Ionisatom potential for a given element is fixed but for different elements, Ionisation potentials are different.

→ Ionisation potential of H-atom = 13.6 V.

→ Impact parameter of the α – particle is defined as the -⊥r distance of the velocity vector of the α – particle from the centre of the nucleus, when it is far away from the atom.

→ Wave number is the number of complete waves in unit length.

→ Ground states is defined as the energy state of electron corresponding to n = 1.

→ The energy states of electrons corresponding*to n = 2, 3…. are called excited states.

→ Excitation energy required, so as to raise an electron from its ground state to an excited state.

→ Ionisation is the process of knocking an electron out of the atom.

→ Ionisation energy is defined as the energy required to knock an electron completely out of the atom.

Formulae

→ Distance of closest approach
r0 = $$\frac{1}{4 \pi \varepsilon_0} \times \frac{Z e^2}{\frac{1}{2} m v^2}$$

→ Impact parameter
b = $$\frac{1}{4 \pi \varepsilon_0} \times \frac{Z e^2 \cot \theta / 2}{\frac{1}{2} m v^2}$$

→ Bohr’s quantisation condition mvr = $$\frac{\mathrm{nh}}{2 \pi}$$

→ Bohr’s frequency conditon hv = Ei – Ef

→ Radius of Bohr’s nth orbit is
rn = 4πε0 $$\frac{n^2 h^2}{4 \pi^2 m e^2}$$

→ Speed of an electron revolving nth orbit is given by υn = $$\frac{1}{4 \pi \varepsilon_0} \frac{2 \pi \mathrm{e}^2}{\mathrm{nh}}$$

→ Rydberg constant
RH = $$\left(\frac{1}{4 \pi \varepsilon_0}\right)^2 \frac{2 \pi^2 \mathrm{me}^4}{\mathrm{ch}^3}$$

→ Energy of electron in nth orbit,
En = $$-\left(\frac{1}{4 \pi \varepsilon_0}\right)^2 \frac{2 \pi^2 \mathrm{me}^4}{\mathrm{n}^2 \mathrm{~h}^2}$$

E = $$\left(\frac{1}{4 \pi \varepsilon_0}\right)^2 \frac{2 \pi^2 \mathrm{me}^4}{\mathrm{~h}^2} \frac{1}{\mathrm{n}_{\mathrm{f}}^2}-\frac{1}{\mathrm{n}_{\mathrm{i}}^2}$$
→ Ionisation potential = $$\frac{\text { Ionisation energy }}{\mathrm{e}}$$