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Lecture 7

Lecture 7.pdf

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Department
Chemistry
Course
CHM120H5
Professor
Thottackad Radhakrishnan
Semester
Winter

Description
Lecture 7 Monday, 20 January, 2014 11:01 AM Today's Topics: Announcements: Homework:   Experiment 1 report (21 Jan) Quiz 1 (21 Jan) Practice questions (21 Jan) Lecture Topic: Practice problem: which of the following combinations of quantum numbers does not describe an allowed orbital? Option n l m(l) 1 1 1 0 2 3 0 0 3 2 1 -1 4 4 3 -2 5 4 2 0 • The answer is option 1 because the azimuthal number, l, must be at least 1 less than the principal quantum number, n. Orbital nodes • A node is a region in space with zero probability of finding an electron ○ It is the result of destructive interference (in a wave) • There are two types of nodes: ○ Angular (a) ○ Planar (b) • To determine radial nodes, you use the equation ○ For 3s, s has an l value of 0, so the number of radial nodes would be 3 - 0 - 1 = 2 radial nodes  n = 3  l = 0 ○ For 3p, it would be 3 - 1 - 1 = 1 radial nodes • They can be graphically represented by plotting the electron density (probability of finding an electron) on the y axis vs.orla on the x axis ○ When y = 0 there is a node • In p orbitals, the term refers to the nodal plane (the plane where there are no electrons to be found) ○ Ex: p xas nodal plane yz • The d orbitals have two nodal planes ○ Ex: d xys nodal planes zx and zy Orbital phases • Wave functions (and therefore orbitals) have a phase: • Orbitals change phase when they cross a node ○ Represent with a colour or sign change The hierarchy of quantum numbers for atomic orbitals Name, symbol (property) Allowed values Quantum numbers Principal, n (size, energy) Positive integer (1, 2, 3…) 1 Angular momentum,l (shape) 0 to n-1 0 Magnetic, m lorientation) -l, …, 0, …, +l 0 Spin, ms -1/2, +1/2
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