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Atomic Spectra A spectroscope is an instrument that disperses the light emitted by an excited gas into the different frequencies the light contains. refraction Wavelengths separated Atomic Spectra An emission spectrum consists of the various frequencies of light given off by an excited substance. Below is the part of the emission spectra of sodium. Atomic Spectra An absorption spectrum consists of the various frequencies absorbed by a substance when white light is passed through it. The frequencies in the spectrum of an element fall into sets called spectral series. Seen here is the spectral series of hydrogen. Origin of Absorption Spectra Spectrum of hydrogen • When energy is supplied to the H gas sample, individual atoms absorb different amount of energy and electron shift to different energy levels, I,e., 3rd, 4th, 5th……. • The electrons are in higher energy levels are relatively unstable and drop back to lower energy levels. • This process of dropping back, energy is emitted in the form of line spectrum containing various lines of particular frequency and wavelength. Spectrum of Hydrogen Electron Waves and Orbits An electron can circle a nucleus only in orbits that contain a whole number of de Broglie Wavelengths. The quantum number n of an orbit is the number of electron waves that fit into the orbit. Electron Waves and Orbits Electrons seemed to be locked into these wave patterns around the nucleus. Quantum Mechanics Erwin Schrödinger (1887-1961) The theory of quantum mechanics was developed by Erwin Schrödinger, Werner. According to quantum mechanics, the position and momentum of a particle cannot both be accurately known at the same time. Only its most probable position or momentum can be determined. The most probable distance between the proton and electron for a hydrogen atom turns out to be about 0.89Å, the same as Niels Bohr. Quantum Numbers and Atomic Orbitals n = principal quantum number (shell) n 1 describes orbital size specifies primary energy level greater n, higher E (like Bohr’s E) l = angular momentum quantum number (subshell)(azimuthal quantum number) describes orbital shape l = 0 = s orbital l = 1 = p orbital inc E l = 2 = d orbital within 0 n -1 l = 3 = f orbital n Quantum Numbers and Atomic Orbitals ml = magnetic quantum number describes orbital orientation m the direction is space also tells the number of orbitals of same energy (degenerate orbitals) So, the combination of n, l, and ml, completely describes a and orientation. specific orbital, its size , shape To make a complete picture, a 4th quantum number added, ms. ms = spin quantum number - describes the electron spin in the orbital ms 1/2 or Quantum Numbers principal quantum number n 1,2,3,….. orbital quantum number l 0,1,2,….n-1 magnetic quantum number m -l to +l for n=2 -2,-1,0,1,2 spin magnetic quantum number +½ or –½ spin Its like your address. To find where you are you need to know 4 things: state, city, street, house #. To know where or what state the electron is in you need to know the four quantum numbers. Quantum #’s are like an Address. What do you need to know to find out where you live? State Principle Quantum # (n) City Angular Quantum # (l) Street Magnetic Quantum # (ml) House Spin Quantum # (ms) Shapes of Atomic Orbitals P orbital d orbital s orbital Quantum Numbers 3py 3d 2py 1s 2s 2px 2pz3pz 3s 3px s and p orbital Movie d orbital Movie Aufbau Principle -For an atom in its ground state ( the lowest energy configuration) fill the lowest energy orbital first then go up in energy until all the electrons are used. Predicting Orbital Filling Diagonal Rule 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 1s2s2p3s3p4s3d4p5s4d….. 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f Energy Levels For H atom 4s_4p_ _ _ 4d_ _ _ _ _4f _ _ _ _ _ _ _ 4s _ All other atoms Inc E 3p _ _ _ 3s _ 3p _ _ _ 3d _ _ _ _ _ Inc E 3d _ _ _ _ _ 3s _ 2p _ _ _ (degenerate orbitals) 2s _ 2p _ _ _(degenerate orbitals) 2s _ 1s _ 1s _ Pauli Exclusion Principle • No two electrons in the same atom can have the same four quantum numbers • Each electron has a unique address • Designated by a set of quantum numbers (n, l ,ml , ms) • So: (1,0,0, +1/2) indicates an electron in a 1s orbital • While (3,1, -1, +1/2) would be a 3p electron Which of the following does not represent a 3d electrons? A. (3,2,1,+1/2) B. (3,2,-1,+1/2) C. (3,1,1,+1/2) D. (3,2,2,-1/2) E. (3,2,0,+1/2) What are the atomic numbers of elements whose outer most electrons are represented by 2p3 and 3p6? N= 1s22s22p3 Ar=1s22s22p63s23p6 Next class Chemical bonding