^Properties of X –rays

1. EM with wavelengths from about 1 A⁰ to 100 A⁰.
2. Travel in straight lie with speed of light.
3. Can under go reflection, refraction, diffraction, interference & polarization.
4. Not deflected by electric & magnetic fields.
5. Produce flourescence.
6. Affect photographic plates.
7. Show photoelectric effect.
8. Can Ionize the gases, destroy animal tissue & white blood cells.
9. Penetrate through different depths into different substances.
10. Don’t pass through heavy metals and bones. If such objects are placed in their path, they cast their shadow.

^Isobars

Are the atoms:

having same:  A, N_N, Physical properties

But different: Element, Z, n_e, n_p , Chemical properties

Examples:    1.  ₁H³ & ₂He³                       2. ₆C¹⁴ & ₇N¹⁴

3.  ₈O¹⁷ & ₉O¹⁷                     4. ₁₁Na²², ₁₀Ne²²

5. ₂₀Ca⁴⁰ & ₁₈Ar⁴⁰                    6. ₁₇Cl³⁷ & ₁₆S³⁷

^Important masses

m_n > m_p ( slightly) m_p > > me , m_p » 1836 m_e

^Bohr correspondence principle

According to this principle the quantum theory must give same result as classical theory in the appropriate classical limit.  

^Limitations of Bohr’s theory

1. It is valid only for single electron system.
2. Nucleus was taken as stationary but it also rotates about its own axis.
3. Couldn’t explain fine structure of spectral line.
4. Provides no information about the relative intensities of spectral lines.
5. Provides no distribution of electrons in an atom.
6. Fails to explain that why do the electrons move only in circular orbits.
7. Bohr’s theory doesn’t explain the Zeeman effect (splitting up of spectral lines in magnetic field) & Stark effect (splitting up of spectral lines in electric field).
8. Bohr’s theory doesn’t explain the doublets in the spectrum of the some atoms e.g. in sodium (5890 A⁰ & 5896 A⁰).
9. Silent about the selection rules which governs the transitions.
10. Use two theories

(i) Quantum (to explain the existence of stationary orbits) &

(ii) Classical (for motion of electrons in the orbits). These two theories essentially oppose each other.