Physics 1202: Lecture 34 Today’s Agenda Announcements: Extra creditsExtra credits –Final-like problems –Team in class –Teams 5 & 6 HW 10 due FridayHW 10 due Friday Atomic Physics

5 steps methods Draw and list quantitites Concepts and equations needed Solve in term of symbols Solve with numbers Checks values and units

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 +e e r F v Newton’s second law Kinetic energy of the electron Total energy of the electron Radius of allowed orbits Bohr’s radius (n=1) Quantization of the energy levels Using

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

Link with matter wave Recall De Broglie wavelength of a particle Must have integer number of wavelength 2  r = n So, using De Broglie expression

Matter waves Various levels n

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