Transcript Shapes of the Charge Clouds

Quantum Theory & Electron clouds
The Hydrogen Atom and Quantum Theory
Niels Bohr (Danish) tried to explain the spectrum of
hydrogen atoms.
•Energy is transferred in photon units (quanta),
therefore specific amounts of energy are absorbed
or emitted
•Because the energy of an electron is quantized
(discreet), there are only certain energy levels
(orbits) for electrons
•Therefore, this e-m radiation can behave as waves
or particles = Wave-Particle Duality Theory
•When an electron gains a certain amount of energy
(absorbs a certain number of photons) it becomes
excited and moves to a higher energy level
If the electron radiates this energy, it jumps back toward
ground (resting) state and emits colored light!!
•The specific amounts of energy released when an electron
jumps from an excited state to a lower state produce light of
certain specific color
The de Broglie Hypothesis
Basic Premise of Quantum Mechanics = small particles
in small regions of space (e-) do NOT behave like large
visible objects.
•Therefore… we cannot tell exactly where an e- is at
any given time or how it got there.
•We CAN predict the position of the e-
Hypothetical example for comparison:
If I want to find you on a Saturday
afternoon…
•Probable places for finding
electrons = ORBITALS
Location
__Probability__
Friend's house
15%
Shopping
10%
McDonald's
15%
Home in bed
30%
Cruising
15%
Work
15%
Working in Chem Lab
0%
•Louis de Broglie (1924) theorized that if light can behave as
particles, then particles (e-) could behave as waves!
•Why?? A wave fills the space of an atom better than a
particle
•As an electron moves closer to the nucleus, its wavelength
shortens, therefore frequency and energy increase - and the
atom doesn't collapse
•Wave-Particle Duality Theory:
greatly affects small particles
whose behavior can be classed as
either wave-like or particle-like
•To explain the position of an
electron, both behaviors must be
considered
•Heisenberg Uncertainty Principle: shows that we
can only predict or estimate the position and momentum of
the electron
•Because we record position by measuring radiant energy
from a particle, we can never know the exact position and
the exact momentum of an electron!!!
Electrons are so small and so easily affected by energy (of
any form) that "lighting up" an electron to see it causes it to
change momentum (position and/or direction)
Wave-Mechanical View of the Hydrogen Atom
•When calculating the position of the electron,
certain areas are more probable than others
•These areas tend to be close to the nucleus
•These areas are cloud-like with a fairly large space
being filled by a few tiny electrons (e.g. fan blades)
•Therefore, the electron cloud
takes up most of the space of
the atom, while the small,
dense nucleus fills the center.
QUANTUM THEORY: shows how the electron
determines an atom's behavior and properties
•Schrodinger's Equation - supports the
theory that quanta of energy are absorbed
and emitted in whole-number units (in simple atoms!!)
•In larger atoms it is assumed that the electrons do not
interfere with each other but they probably do (at least a
little bit)
•4 Quantum Numbers must be used to describe the position
of the electrons in an atom
•n, l, m, s are the "numbers"
Each electron has a different set (just like each locker out in
the hall has a different combination)
•Principle Quantum Number -
n
•Identifies the major energy levels that
electrons can occupy
•Shows the distance from the nucleus
•Numbered 1,2,3,4,5,6,7,8 but sometimes
referred to as K,L,M,N,O,P,Q,R shells
•Equation: 2n2 - shows how many electrons can be in
each energy level (e.g. level 3: 2(3)2 = 18 e-'s)
•Orbital Quantum Number - l
•Identifies the shape of the sublevels of the main
energy levels
•s, p, d, f - used to identify the shape = "sphere,
peanut, double peanut, flower"
•1st energy level has 1 subshell (s)
•2nd energy level has 2 subshells (s,p)
•3rd energy level has 3 subshells (s,p,d)
•4th energy level has 4 subshells (s,p,d,f)
•At higher energies, these orbitals overlap
•l can be from 0 to n-1
•s=0
•p=1
•d=2
•f=3
Shapes of the Charge Clouds
s for "Sphere": simplest shape, or shape of the
simplest atoms like hydrogen and helium
•Electrons don't interfere with, or block, each other
from the pull of the nucleus - ball shape
•Each energy level has an "s" orbital at the lowest
energy within that level
Shapes of the Charge Clouds
•p for "Peanut": more complex shape
that occurs at energy levels 2 and
above
Shapes of the Charge Clouds
d for "Double Peanut": complex shape
occurring at energy levels 3 and above
The arrangement of these orbitals allows for
"s" and "p" orbitals to fit closer to the
middle/nucleus
Shapes of the Charge Clouds
f for "Flower": 7 bizarre-shaped orbitals for
electrons of very large atoms
•electrons filling these orbitals are weakly
attached to the atom because they are so far
away from the pull of the nucleus
Magnetic Quantum Number
m
•Is indicated by the orientation of these orbitals in
each dimension.
•"p" orbitals line up on the x, y, z, axes in space
•"d" and "f" orbitals can line up on the axes as well as
in between them
•Equation: there are n2 orbitals (of various shapes)
per energy level
•e.g. level 3 has 32 = 9 orbitals (one s, 3 p's, 5 d's)
•m can be from –l to +l
•s orbital can have only one orientation (subshells)
•m can be 0 only, meaning 1 possible orientation in space
•p orbital can have 3 different orientations (subshells)
•m can be -1, 0, +1, meaning 3 possible orientations in space
•d orbital can have 5 different orientations (subshells)
•m can be -2, -1, 0, +1, +2 meaning 5 possible orientations in
space
•f orbital can have 7 different orientations (subshells)
•m can be -3, -2, -1, 0, +1, +2, +3 meaning 7 possible
orientations in space
•Spin Quantum Number (s): indicates the
clockwise or counterclockwise spin of the
electron
•Designated by -1/2 or +1/2
•Needed because NO 2 ELECTRONS CAN
HAVE THE SAME SET OF QUANTUM
NUMBERS!
•Sometimes called left-handed or righthanded spin
Pauli Exclusion Principle
•No two electrons in an atom have the same
set of 4 quantum numbers!
•Therefore, only 2 electrons can fit in any one
orbital
•This works because spinning electrons act like
tiny electromagnets and magnetically attract
each other when they have opposite spin
Aufau Principle
•Electrons fill the lowest energy levels first
(always)
•As principle quantum number increases, spacing
between the shells decreases
•Therefore, the third subshell and beyond start to
overlap energy levels
Hund's Rule = electrons entering a
subshell containing more than one
orbital will spread out over the
available orbitals with their spins in
the same direction until all orbitals
have one electron in them
Order of Fill for sublevels
•Three ways to describe the
electron structure of atoms in
the ground state: orbital notation,
electron configuration notation,
electron dot notation