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Lecture

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

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University of Guelph

Chemistry

CHEM 1040

Adrian Schwan

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 , λm, 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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