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Chapter 4 Arrangement of Electrons In Atoms

Properties of Light Light as a wave –D–Diffraction –I–Interference Light as a particle –P–Photoelectric effect Dual Nature of Light – light can behave as both a wave and a particle. –E–Electromagnetic Radiation – energy that travels through space as a wave You can treat it three ways

Electromagnetic Spectrum

Wave Diagram

Wave Mechanics Wavelength – – distance between corresponding point on adjacent waves (m) Frequency – –– (f) – number of waves that pass a certain point in a given time (waves/s) or (/s, s -1 ) or (Hz) Speed of a wave = v = –F–For lightc= (c=3x10 8 m/s)

Proof Light is a Wave Diffraction – bending of a wave around a barrier. Interference – combining of waves that cross paths (superposition).

Proof Light is a Particle Photoelectric effect – emission of electrons from a metal when the metal is struck by certain frequencies of light. E  E = h –h–h–h–h = 6.626x10-34 Js –P–P–P–Plank’s Constant

E = h E = h c =   c /  c / E = h c / E = h c / Niels Bohr – explained the spectral lines observed in excited gases Hydrogen Emission Spectrum

Balmer, Paschen, and Lyman Series

The DeBroglie Hypothesis If light can behave as both a w ww wave and a particle, can electrons also have this dual nature?

The Quantum Model Heisenberg’s Uncertainty Principle Heisenberg’s Uncertainty Principle – it is impossible to know both the exact position and the momentum (velocity) of a small particle at the same time. Schrodinger’s Wave Equation Schrodinger’s Wave Equation – describes the probability of finding an electron at some distance from the nucleus in terms of the wave function 

Implications of Heisenberg and Schrodinger These ideas say it is impossible to know where an electron is at any point in time. Therefore we can only say where an electron is most probably located at any time. We call that region an orbital. Orbital – 3d region around a nucleus where an electron is likely to exist

Quantum Numbers – 4 numbers used to describe the location of an electron Principle Quantum Number – (n) – tells the main energy level of the electron. Angular Momentum Quantum Number – (l) – describes the shape of the orbital. Magnetic Quantum Number – (m) – tells the orientation of the orbital around the nucleus. Spin Quantum Number – (s) – indicates the direction of the spin of the electron on its own axis.

Pauli’s Exclusion Principle – No two electrons have the same set of 4 quantum numbers Possible values for the quantum numbers –n–n = 1,2,3,…7 max # of e - in energy level =2n2 –l–l = n-1l = 0,1,2,…6 or s,p,d,f,g… –m–m = (-l,…0…+l) –s–s = +/- 1/2

Principle Quantum Number Tells the main energy level (how far from the nucleus) of an electron #e - /energy level = 2n 2

Angular Momentum Quantum Number – Azimuthal Quantum Number Tells the type (shape) of the orbital

Magnetic Quantum Number Magnetic Quantum Number – tells orientation around the nucleus

Spin Quantum Number s = -1/2s = +1/2

Electron Configurations – shorthand way of representing the arrangement of electrons in an atom Pauli’s Exclusion PrinciplePauli’s Exclusion Principle – no two electrons have the same set of four quantum numbers (everybody’s different) Aufbau Principle – electrons occupy the lowest possible energy level (electrons are lazy) Hund’s Rule – orbitals of equal energy are occupied by one electron before any one orbital is occupied by two electrons, and all electrons in singly occupied orbitals have the same spin (everybody gets one before anybody gets two)

Order of Orbital Filling

Helium ?? Electron Configurations for 1 st Period 2+

Notations for 2 nd and 3 rd Periods

Orbital Notation

Orbitals Notations for 3p’s

Periodic Table with Electron Configurations

Noble Gas Notations Here are some examples: O 1s 2 2s 2 2p 4 Si 1s 2 2s 2 2p 6 3s 2 3p 2 Ca 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 Cr 1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 4s 1 Br 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 5 La 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 4f 1 5s 2 5p 6 6s 2 O [He]2s 2 2p 4 Si [Ne]3s 2 3p 2 Ca [Ar]4s 2 Cr [Ar]3d 5 4s 1 Br [Ar]3d 10 4s 2 4p 5 La [Xe]4f 1 6s 2. O [He]2s 2 2p 4 Si [Ne]3s 2 3p 2 Ca [Ar]4s 2 Cr [Ar]3d 5 4s 1 Br [Ar]3d 10 4s 2 4p 5 La [Xe]4f 1 6s 2.

Homework Pages 124-126 Numbers 6,10,11,14,18,19,22,30,31,32,33,35,37,38, 46,48,50

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