2.1_atoms_and_molecules_post

2.1_atoms_and_molecules_post - Vollhardt: Chapter 1 Bohr...

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Sec. 2.1 - Atoms and Molecules 1 Structure of atoms (NE 122 Review) Bohr Electrons around a nucleus can be only in discrete orbits and they absorb or emit energy in discrete amounts as they move from one orbit to another. Each orbit thus corresponds to a definite energy level for the electron. Absorption of electromagnetic radiation promotes an electron to higher energy level Emits exactly the same amount of energy when the electron drop back to the lower energy level Calculations could be completed for simple molecules He + , Li 2+ , but could not calculate the energy levels for more complex molecules because orbitals were assumed to be spherical . Vollhardt: Chapter 1
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Sec. 2.1 - Atoms and Molecules 2 Then came Quantum Mechanics The basics 1) Atoms or molecules can only exist in certain energy states. When an atom or molecule changes its energy sate, it must emit or absorb just enough energy to bring it to a new energy state. (the quantum condition) 2) The energy change in the atom or molecule is related to the frequency or wavelength of the light emitted or absorbed by the equation Δ E = h ν or Δ E = hc/ λ . Which is equal to the energy of a photon emitted or absorbed during the transition. 3) The allowable states of atoms and molecules can be described by sets of numbers called quantum numbers Electrons travel in waves and can be described by the Schrodinger equation or a wave function Ψ . Quantum numbers describe the electron configuration of an atom or molecule and also describes the shape of the orbitals.
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Sec. 2.1 - Atoms and Molecules 3 Principle main energy level Subsidiary designates shape or region of space electron occupies Magnetic special orientation Spin Electron Capacity of sublevel Electron Capacity of Energy Level n l m l m s = 4l+2 2n 2 1 0 ( 1s ) 0 + ½ , - ½ 2 2 2 0 ( 2s ) 0 + ½ , - ½ 2 8 1 ( 2p ) -1, 0, +1 ± ½for each m l 6 p x , p y , p z 18 3 0 ( 3s ) 0 ± ½ 2 1 ( 3p ) -1, 0, +1 ± each m l 6 2 ( 3d ) -2, -1, 0, +1, +2 ± each m l 10 Quantum Numbers
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Sec. 2.1 - Atoms and Molecules 4 The probability of finding an electron is the square of the wave function ( Ψ 2 ). The electron density is proportional to r 2 Ψ 2 . r = radius from nucleus r 2 Ψ 2 (3s) (1s) (2s) An elegant orbital visualization resource, created at MIT can be found at: http://web.mit.edu/3.091/www/orbs/
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Sec. 2.1 - Atoms and Molecules 5 + - n = 2 l =1 p x p y p z m 1 = -1, 0 +1
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Sec. 2.1 - Atoms and Molecules 6 Periodic Table Build up the periodic table by adding protons, neutrons and electrons to give the lowest total energy for the atom. No two electrons can have the same set of quantum numbers Electronic Configuration 1s 2s 2p 3p 4p 3d 3s 4s 4d 4f 7 obitals PE Orbitals that have the same energy level are called degenerate.
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Sec. 2.1 - Atoms and Molecules 7 What is the ground-state electronic configuration of Carbon ( 6 C)?
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This note was uploaded on 07/18/2011 for the course NE 122 taught by Professor Nano during the Winter '09 term at Waterloo.

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2.1_atoms_and_molecules_post - Vollhardt: Chapter 1 Bohr...

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