Transcript Unit 3 notes

General Chemistry Unit 3
ELECTRONS IN ATOMS
I. RADIATION
A. Particles
 1. alpha particle - helium nucleus with
2 protons, 2 neutrons
 2. beta particle - electron or positron ejected
from nucleus
 B. Energy - gamma rays (like x-rays)
II. SPECTRA
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
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A. EM (electromagnetic) energy
Equations:
E = hv
v = frequency (Hz)
E = energy
h = Planck's constant (6.626 x 10-34 J/Hz)
λ = c/v


c = speed of light (3.00 x 108 m/s)
 λ = wavelength (nm)
 Relationships: E/v = constant (direct)
λv = constant (inverse)
E and λ are inversely related
So high energies are associated with high frequencies and
lower wavelengths

EXAMPLE
What is the wavelength of light (in nm) whose
frequency is 7.500 x 1012 Hz?
 λ = c/ν
 So λ = 3.00 x 108 m/s = 4.00 x 10-5 m
7.500 x 1012 /s
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TYPES OF SPECTRA
B. Emission spectrum: wavelength given off
by energized electrons in the element
 Ground state: lowest energy state of an atom
 Excited state: atom has higher potential
energy than in ground state
 C. Absorption spectrum: wavelength
absorbed as light passes through the element
vapor (same lines as in emission)
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SPECTRA EXAMPLES
III HISTORY OF QUANTUM MECHANICS
A. wave-particle duality of nature - we only see
the wave nature when particles are small and
velocity is near c (speed of light)
 B. Heisenberg uncertainty principle - the more
you know about position the less you know
about momentum
 C. Found the probability of an
electron's position at any time
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IV. QUANTUM NUMBERS - DESCRIBE AN ELECTRON
IN 4 WAYS:
1. energy level (distance from nucleus)
 2. sublevel (orbital shapes)
 s is sphere shape
 p is peanut shape
 d is double peanut shape
 f is flower shape
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IV. QUANTUM NUMBERS - DESCRIBE AN ELECTRON
IN 4 WAYS:

3. orbital position in space (x,y,z axes)
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 4.
each orbital can hold two electrons
 s sublevel has 1 orbital
 p sublevel has 3 orbitals
 d sublevel has 5 orbitals
 f sublevel has 7 orbitals
spin – clockwise or counterclockwise
A. PAULI EXCLUSION PRINCIPLE:
 No
two electrons in the same
atom can have the same four
quantum numbers
 Must have opposite spins if
they are in the same orbital
B. APARTMENT BUILDING ANALOGY
Energy Level - Floor
 Orbital shape (sublevel) – Type of
Apartment: s -1 bedroom, p-3 bedroom, d-5, f-7
 Orbital position - Which bedroom in apartment
(1 person in each room before adding a
roommate)
 Spin - Which bed in bedroom? Bed by window is
first taken (clockwise), bed by door
(counterclockwise)
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V. ELECTRON FILLING ORDER - RULES
1. Aufbau Principle: electrons will occupy lowest
energy levels and shapes first (follow diagram)
 2. Hund’s Rule: electrons will be alone in an
orbital if possible - put one in each equal
energy orbital before doubling up in any orbital
in the same sublevel
 Orbitals with the same energy requirement are
called degenerate orbitals
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3. EXAMPLE: OXYGEN
 Atomic
number 8, so has 8 electrons
 Assign apartments for each electron (see
board)
B. QUANTUM SHORTHAND
1. Orbital Notation - shows all properties
described by the four quantum numbers 1s
 Orbitals shown by line, electron represented by
arrow (up-clockwise, down-counterclockwise)
 2. Electron Configuration - shows electrons
down to the sublevels
 Energy level and sublevel with superscript of
how many electrons present
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1s22s22p6
C. SHORTHAND EXAMPLES

See board
3. ELECTRON DOT NOTATION
Shows outer energy level only (energy level with
the highest number in front)
 a. Dot arrangement: symbol goes in the center
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E
(draw in numbers to show dot order)
 b. 8 dots maximum: next energy level begins to
fill after the p sublevel - only highest level is
shown even if lower level is not complete
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NOBLE GAS CONFIGURATION
Begin the configuration with the symbol for the
noble gas from the row above your element.
Put it in brackets with the number of electrons
above it (the atomic number of the gas).
 Beginning with the s level of the period that
contains your element, continue to fill orbitals
until the total number of electrons (all
superscripts added together) matches your
element’s atomic number.
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EXAMPLES
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Phosphorus – Atomic number 15
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Find noble gas above P – put in brackets
 [Ne]
(has 10 electrons already – only need to show 5
more)
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Start with s electrons on energy level of period that
P is on
 3rd
period – so begin with 3s electrons
 Continue filling until electrons equal atomic number
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[Ne] 3s23p3
Indium – Atomic number 49
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[Kr] 5s24d105p1
END OF UNIT 3
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