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CHEM 1040 (192)
Lecture

# Atomic Structure and Periodic Trends: Lectures during Week 1-2

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School
University of Guelph
Department
Chemistry
Course
CHEM 1040
Professor
Semester
Fall

Description
Atomic Structure Light and Spectroscopy The interaction of atoms or molecules with light is well documented: Examples include heated metals that give off light, ambient light effects, chemiluminescents, light bulbs, glow in the dark material. Important clues to the structure of atoms can come from analyzing emmisions or absorption of heat by atoms. Light: Fluctuating electric and magnetic fields that are perpendicular to the motion of the wave and to eachother. Possesses energy defined in formulaic form as: ×v carrying units of Joules (J) Described in terms of wavelength and frequency h is Planck's constant -34 h = 6.63 x 10 J s Planck proposed that electromagnetic irradiation come in packets of defined energy. Therefore light is quantized. Units: c m s , λm, v  s -1 "c" is the velocity of light: 300000000m/s in a vacuum The unit s = 1/s = reciprocal time (“per second”) Given the special name hertz, abbreviated Hz : 1 Hz = 1 s -1 (also know as cycles per second) Example: What is the frequency of yellow light of wavelength 625 nm? c = λ×v v = c/λ nm = nanometer = 10e-9 so 625 nm = 625e-9 m v = 3.00e8 m/s / 625e9 m v = 4.8e14 Hz de Broglie suggested that the movement of small particles such as photons could be described as waves Schrödinger set up the equations to describe wave motion of atoms. Part of these equations are quantum numbers which define energy and 3-dimensional position of electrons in space. (where finding an electron is of high probability) Quantum Model (sub-orbits within orbits) S – holds max 2 electrons P – holds max 6 electrons d – holds max 10 electrons f – holds max 14 electrons Principal quantum number n - represents the main energy level of an electron - higher n value means it is further away from nucleus and the orbitals have higher energy - permitted values of n are 1,2,3,4…etc - represented by a letter K,L,M,N  Angular Momentum quantum number l - divides shells into smaller subshells - helps define the shape of the orbital/electron cloud - l = 0, spherical shape (S orbital) - l = 1, dumb-bell shape (p orbital) - l = 2, variety of shapes (d orbital) - permitted values of l range from 0-(n-1) i.e. n=4, l=0,1,2,3 MAGNETIC Quantum Number m l - indicates permitted orbitals/group - range for ml= -l to +l - m lpecifies the permitted orientations in space of an electron cloud - It tells you how many sub-levels there can be for any l value Spin Quantu
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