An Outline of the Atomic Theory

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SCC-CH110/UCD-CH41C Chapter: 10 Instructor: J.T. P1 An outline of the atomic theory: In 1990 Max Planck gave the name quantum to the smallest quantity of energy that can be emitted or adsorbed as electromagnetic radiation, E = h ν. In 1910 Rutherford discovered the nuclear nature of the atom. In 1913 N. Bohr described his planetary model for the H- atom. o Only orbits of certain radii, corresponding to certain definite energies, are permitted for electrons in an atom. o An electron in an allowed energy state will not radiate energy. o Energy is only emitted or absorbed by an electron as it changes from one allowed energy state to another. Bohr Model Limitations o It offers an explanation only for the line spectrum of H-atom. o There is a problem with describing an electron circling about the nucleus. In 1924, L. de Broglie suggested that the matter in motion are associated with waves, λ = h /mv In 1926, Schrödinger proposed an equation that incorporates both the wavelike and particle-like behavior of the electron (quantum mechanics). SCC-CH110/UCD-CH41C Chapter: 10 Instructor: J.T. P2 Orbitals and quantum numbers: The solution to Schrödinger’s equation for the hydrogen atom yields a set of wave functions or orbitals. The Bohr model introduced a single atomic number n to describe an orbit. The quantum mechanical model uses n, l, and m to describe an orbital. Quantum Numbers: Symbol n Name Principal quantum number Values 1, 2, 3, .. description Defines the size of the orbital -18 2 Note For the Bohr model: En= - 2.18x10 J(1/n ) Symbol l Name Azimuthal quantum number Values From 0 to (n-1) Description Defines the shape of the orbital Note The value of l 0 1 2 3 Letter used s p d f Symbol m Name Magnetic quantum number Values From l to -l , including zero Description Defines the orientation of orbital in space -18 2 Note For the Bohr model: En= - 2.18x10 J(1/n ) i.e.: l=2 m: 2, 1, 0, -1, -2 SCC-CH110/UCD-CH41C Chapter: 10 Instructor: J.T. P3 The Heisenberg’s principle (uncertainty principle): It is impossible for us to know simultaneously both the exact momentum of the electron and its exact location in space. The Pauli exclusion principle: An orbital can hold a maximum of two electrons. 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 5g 6s 6p 6d 6f 6g 6h SCC-CH110/UCD-CH41C Chapter: 10 Instructor: J.T. P4 Electron Configuration: 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f Example: (Al, Z=13) Al: 1s2, 2s2, 2p6, 3s2, 3p1 Because the electron configuration of neon is Ne: 1s2, 2s2, 2p6 Al: [Ne] 3s2, 3p1 Example: electron configuration of calcium: Ca, Z=20: 1s2, 2s2, 2p6, 3s2, 3p6, 4s2 Or: [Ne] 3s2, 3p6, 4s2 SCC-CH110/UCD-CH41C Chapter: 10 Instructor: J.T. P5 The total number of s and p electrons in the highest occupied energy level are called valence electrons. Highest electron level for Al, is 3 (3s & 3p) Highest electron level for Ca, is 4 (4s) .

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