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The Electronic Structure of Atoms Chapter 4 Properties of Waves Wavelength (l) is the distance between identical points on successive waves. Amplitude is the vertical distance from the midline of a wave to the peak or trough. 7.1 Properties of Waves Frequency (n) is the number of waves that pass through a particular point in 1 second (Hz = 1 cycle/s). The speed (u) of the wave = l x n 7.1 7.1 A photon has a frequency of 6.0 x 104 Hz. Convert this frequency into wavelength (nm). Does this frequency fall in the visible region? l lxn=c n l = c/n l = 3.00 x 108 m/s / 6.0 x 104 Hz l = 5.0 x 103 m l = 5.0 x 1012 nm Radio wave 7.1 Mystery, “Photoelectric Effect” Solved by Einstein in 1905 Light has both: 1. wave nature 2. particle nature hn KE e- Photon is a “particle” of light 7.2 Line Emission Spectrum of Hydrogen Atoms 7.3 7.3 Bohr’s Model of the Atom (1913) 1. e- can only have specific (quantized) energy values 2. light is emitted as emoves from one energy level to a lower energy level 7.3 E = hn E = hn 7.3 Chemistry in Action: Element from the Sun In 1868, Pierre Janssen detected a new dark line in the solar emission spectrum that did not match known emission lines Mystery element was named Helium In 1895, William Ramsey discovered helium in a mineral of uranium (from alpha decay). Chemistry in Action: Laser – The Splendid Light Laser light is (1) intense, (2) monoenergetic, and (3) coherent Chemistry in Action: Electron Microscopy le = 0.004 nm STM image of iron atoms on copper surface Schrodinger Wave Equation In 1926 Schrodinger wrote an equation that described both the particle and wave nature of the eWave function (Y) describes: 1. energy of e- with a given Y 2. probability of finding e- in a volume of space Schrodinger’s equation can only be solved exactly for the hydrogen atom. Must approximate its solution for multi-electron systems. 7.5 Order of orbitals (filling) in multi-electron atom 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s 7.7 “Fill up” electrons in lowest energy orbitals (Aufbau principle) ?? Be Li B5 C 3 64electrons electrons 22s 222s 22p 12 1 BBe Li1s1s 1s 2s H He12electron electrons He H 1s 1s12 7.7 The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins (Hund’s rule). Ne97 C N O F 6 810 electrons electrons electrons 22s 222p 22p 5 246 3 Ne C N O F 1s 1s222s 7.7 Electron configuration is how the electrons are distributed among the various atomic orbitals in an atom. number of electrons in the orbital or subshell 1s1 principal quantum number n angular momentum quantum number l Orbital diagram H 1s1 7.8 What is the electron configuration of Mg? Mg 12 electrons 1s < 2s < 2p < 3s < 3p < 4s 1s22s22p63s2 2 + 2 + 6 + 2 = 12 electrons Abbreviated as [Ne]3s2 [Ne] 1s22s22p6 What are the possible quantum numbers for the last (outermost) electron in Cl? Cl 17 electrons 1s22s22p63s23p5 1s < 2s < 2p < 3s < 3p < 4s 2 + 2 + 6 + 2 + 5 = 17 electrons Last electron added to 3p orbital n=3 l=1 ml = -1, 0, or +1 ms = ½ or -½ 7.8 Outermost subshell being filled with electrons 7.8 7.8