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Chemistry

CHEM 101

Ruth Topich

Spring

Description

Exam 3 Material
Periodicity and the Electronic Structure of Atoms
Wavelength- the distance between successive wave peaks
Frequency- the number of wave peaks that pass a given point per unit time
Amplitude- the height of the wave maximum from the center
What we perceive as different kinds of EM energy are waves with different wavelengths
and frequencies
Wavelength x frequency = speed of light (3.00 x 10^8 m/s)
o Wavelength in meters (m)
o Frequency in /s (1 /s = 1Hz)
Example: What is the wavelength associated with a frequency of 106.5 MHz?
o 106.5 MHz= 106.5 x 10^6 Hz
=106.5 x 10^6 /s
Example: ?= v (frequency) of red light with a wavelength of 700nm (1nm= 1 x 10^-9 m)
o V= 4.29 x 10^14 Hz
Particles of light = photons
E=hv per photon
o h= Planck’s constant (6.626 x 10^-34 J•s)
o Ex: ? = energy associated with a photon of light with a wavelength = 700 nm red
V= 4.29 x 10^14 Hz
E=hv: E= (6.626 x 10^-34 J•s)(4.29 x 10^14 /s) E= 2.84 x 10^-19 J per photon
Note: you could also be asked in J/mol of photons or kJ/mol of phtons
1.71 x 10^5 J/mol x 1 kJ/ 1000 J = 171 kJ/mol of photons
Ex: ? = E associated with a photon of light with a wavelength = 2.625 x 10^3 nm:
o Equation: E=hc/wavelength (in m)
o C= 3.00 x 10^8 m/s (you must convert nm m)
C= 2.625 x 10^3 nm x 1x10^-9m/1 nm= 2.625 x 10^-6m
E= (6.626 x 10^-34 J•s)(3.00 x 10^8 m/s)/ 2.625 x 10^-6 m
E= 7.57 x 10^-20 J/photon
Bohr Model
o When energy is absorbed by an electron it jumps up a level (or rung on the
ladder)
o Energy given off is a higher number to a lower number (largest is 21)
o Lyman series (UV) has largest amount of energy
Balmer series (vis)
Paschen series (IR)
o Shortest wavelength = furthest drop on ladder because of highest energy
content
Quantum Mechanics
o Wave function is characterized by 3 parameters
Quantum numbers n, l, m Describes energy level and 3-dimensional shape of region
N=1 is closest to nucleus
o Shape of orbitals:
S-orbital (theres one in every energy level) (spherical):
1s belongs to n=1 0 nodes
2s:n=2 1 node
3s: n=3 2 nodes
Note: node is area in space where you cannot find an electron (#
nodes= n-1)
2p-orbitals (shaped like figure 8) (come in groups of 3):
have equal energy
the principle quantity: #s=# subshells
D-orbitals (come in groups of 5) (four leaf clover shape):
Dxy, dyz, and dxz have lobes between axes
Dx^2-y^2 has lobes on every axis
Dz^2 has figure 8 on z axis and a ring around the middle
Principle Energy Level Orbitals
N=1 1s (1)
N=2 2s (1)
2p (3)
N=3 3s (1)
3p (3)
3d (5)
N=4 4s (1)
4p (3)
4d (5) 4f (7)
N=5 5s (1)
5p (3)
5d (5)
5f (7)
5g (9)
N^2= total orbitals
o Total number of electrons in a particular level= N^2 x 2
o E.g. (4)^2 x 2= 32
How are the orbitals in atoms occupied?
o Aufbau principle
o Pauli Exclusion Rule- an orbital can only hold 2 electrons
o Hund’s Rule- if 2 or more degenerate orbitals, 1 electron goes into each until all
are half full
2 different ways to express with Hund’s Rule:
electron configuration: 1s^1
orbital filling diagram
o valence electrons are the only ones to be involved in chemical bonding
(outermost shells)
inert gas: full outer shell (nonreactive)
26 Fe is an example of a paramagnetic element- having unpaired electrons
o diamagnetic- all electrons are paired
Anomalous Electron Configuration o There are 19 but you only need to know these 5:
24 Cr (similar- Mo): 4s^1 3d^5
29 Cu (similar- Ag): 4s^1 3d^10
also the one to the right of Mo but not really
Quantum Num

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