4 11 2010 Chapter 28 Atomic Physics 28 1 Early models of atom J J Thomson s model of the atom A volume of positive charge Electrons embedded throughout the volume Rutherford s Planetary model Positive charge is concentrated in the center of the atom called the nucleus Electrons orbit the nucleus like planets orbit the sun Rutherford s electrons are undergoing a centripetal acceleration 28 3 The Bohr model His model includes both classical and quantum physics ideas His model included an attempt to explain why the atom was stable The electron moves in circular orbits around the proton under the influence of the Coulomb force of attraction The Coulomb force produces the centripetal acceleration Only certain electron orbits are stable The energy of the atom remains constant in these orbits Radiation is emitted by the atom when the electron jumps from a more energetic initial orbit to a lower energy orbit and is given by Ei Ef h 1 4 11 2010 Bohr Radius and energy 2 4 11 2010 Specific Energy Levels The energy of any orbit is En 13 6 eV n2 The lowest energy state is called the ground state This corresponds to n 1 Energy is 13 6 eV The next energy level has an energy of 3 40 eV The energies can be compiled in an energy level diagram The ionization energy is the energy needed to completely remove the electron from the atom The ionization energy for hydrogen is 13 6 eV The uppermost level corresponds to E 0 and n For the Balmer series nf 2 For the Lyman series nf 1 Whenever an transition occurs between a state ni to another state nf where ni nf a photon is emitted The photon has a frequency f Ei Ef h and wavelength 1 RH 1 n2f 1 ni2 Hydrogen like atoms Bohr s model explained several features of the hydrogen spectrum Can be extended to hydrogen like atoms Those with one electron 2 2 Ze needs to be substituted for e in equations E n 13 6eV Z is the atomic number of the element Z2 n2 3 4 11 2010 Example A photon is emitted when an electron in the hydrogen atom jumps from n 3 state to n 2 state Calculate the energy wavelength and frequency of the photon 28 4 Quantum Mechanics and the Hydrogen Atom n principle quantum number l orbital quantum number ml orbital magnetic quantum number ms spin magnetic quantum number n l ml ms Where is the electron You need to know n l ml and ms Based on the restrictions for the quantum numbers that jumped out of the Schr dinger equation n 1 2 3 l 0 1 2 n 1 ml l 2 1 0 1 2 l ms 1 2 1 2 Example For n 1 l 0 ml 0 ms 1 2 ms 1 2 4 4 11 2010 n 1 2 3 l 0 1 2 n 1 ml l 2 1 0 1 2 l ms 1 2 1 2 Example l 1 For n 2 ml 1 ms 1 2 ms 1 2 ml 0 ms 1 2 ms 1 2 ml 1 ms 1 2 ms 1 2 ml 0 ms 1 2 ms 1 2 Shell l 0 Subshell 28 5 The Pauli Exclusion Principle The state of any electron in any atom can be specified by n principle quantum number l orbital quantum number ml orbital magnetic quantum number ms spin magnetic quantum number Pauli s exclusion principle No two electrons in an atom can ever have the same set of values of the quantum numbers n m and ms Filling Shells As a general rule the order that electrons fill an atom s subshell is Once one subshell is filled the next electron goes into the vacant subshell that is lowest in energy A subshell is filled when it holds 2 2 1 electrons 5 4 11 2010 Table 28 3 p 903 The Periodic Table The outermost electrons are primarily responsible for the chemical properties of the atom Mendeleev arranged the elements according to their atomic masses and chemical similarities The electronic configuration of the elements explained by quantum numbers and Pauli s Exclusion Principle explains the configuration 6 4 11 2010 Table 28 4 p 904 28 7 Atomic Transitions and Lasers hydrogen Helium Argon neon 7