Physics 1202: Lecture 36 Today’s Agenda Announcements: Extra creditsExtra credits –Final-like problems –Team in class –Teams 8, 9 & 10 HW 10 due Friday next weekHW 10 due Friday next week Atomic Physics: finally !

Atomic Physics

Bohr’s quantum model of atom +e e r F v 1. Electron moves in circular orbits. 2. Only certain electron orbits are stable. 3. Radiation is emitted by atom when electron jumps from a more energetic orbit to a low energy orbit. 4. The size of the allowed electron orbits is determined by quantization of electron angular momentum

Bohr’s quantum model of atom Orbits of electron in Bohr’s model of hydrogen atom. An energy level diagram for hydrogen atom Frequency of the emitted photon Dependence of the wave length

Quantum numbers Numbers used to describe a quantum state –E n = - E 0 n -2 with E 0 = 13.6 eV –n : principal quantum number Angular momentum L –Classically, any value Quantum mechanically –Quantized (Bohr model): Discrete values –where l = 0,1,2,… and l < n

Quantum numbers Hydrogen ground state with n=1 – l = 0,1,2,… and l < n implies l = 0 only (called s) –n = 2 implies l = 0 or 1 (called s and p) –n = 3 implies l = 0, 1, or 2 (called s, p, and d) Quantization axis –Magnetic field along z –Projection on z - l < m < + l

Electron spin Electron has an intrinsic angular momentum: spin with m s = ± ½

Pauli exclusion principle Wolfgang Pauli (1925): Nobel 1945 –No electron can be in the same quantum state –No more than 2 electrons in an orbital –For a given n, l, m with m s = ± ½ Explains the periodic table –Electronic configuration –Shell structure of atoms

Periodic table Atomic structure and chemical properties –Pauli principle: atomic shell model

X-ray emission from atoms X-ray tube –Discovered by Wilheim Röntgen (1895) –Accelerated electrons hit targets –Large potentials kV to MV

X-ray emission from atoms Bremsstrahlung –Continuous x-ray –Electron loosing energy Minimal –When all initial K is lost

X-ray emission from atoms K, L, etc. shells and x-ray emission –Fast electron kick inner electron out –Higher electron falls in and fill the “hole” –X-ray emitted

X-ray emission from atoms Each element has a specific spectra min