electromagnetic radiation
form of energy, travel as waves, e g radio waves, visible light, UV, gamma rays.
atomic emission spectrum or...
line spectrum
electrons and line spectrums
electrons in atoms of elements have certain energy levels in which they can exist. when they become excited, they jump to higher energy levels. Because they can't stay excited forever, they fall back down to certain energy levels, and the energy they lose
Just like all matter is made of atoms...
all electromagnetic energy is made of photons
quantum
little individual units
what is light composed of?
Perpendicular oscillating waves, one for the electric field and one for the magnetic field. An electric field is where an electrically charged particle experiences force. A magnetic field is where a magnitized particle experiences a force.
At what speed do all electromagnetic waves move?
3.00 X 10 ^8 m/s in a vacuum = the speed of light
node
A point of zero amplitude on a standing wave
trough
Lowest point of a wave
crest
Highest point of a wave
amplitude
The height of a wave or the distance from node to crest or node to trough
What is amplitude a measure of?
How intense the light is, the larger the amplitude, the brighter the light
Wavelength
a measure of the distance covered by a wave, or the distance from one trough to the next, or one crest to the next, or the distance between alternate nodes. Signified by lambda
lambda
What does wavelength determine?
Color
Frequency
The number of waves that pass a point in a given period of time.
Number of waves = number of cycles
Units are hertz (Hz) or cycles/s = s^-1
1 Hz = 1 s^-1
Signified by nu (looks like v)
What is total energy proportional to?
amplitude and frequency of wave
The larger the wave amplitude, the more force it has
The more frequently the waves strike, the more total force there is
Relationship between frequency and wavelength
For waves traveling at the same speed, the shorter the wavelength, the more frequently they pass
This means that wavelength and frequency of electromagnetic waves are inversely proportional
Since the speed of light is constant, if we know wavelength we ca
Eq. for frequency and wavelength
Frequency = speed of light/wavelength
Is red light (closer to infrared) or blue light (closer to ultra violet) higher energy?
Blue light
electromagnetic spectrum from least energetic to most
radio waves, microwaves, infrared, ultraviolet, x-rays, gamma rays
Color of light is determined by...
its wavelength or frequency
What is white light?
A mixture of all the colors of visible light, so it is not a line spectrum. Red orange yellow green blue violet
What is observed color of objects?
When an object absorbs some of the wave lengths of white light while reflecting others, it appears colored. The observed color is predominantly the color reflected.
Photoelectric effect
The emission of electrons from a metal when light shines on the metal
What was the mystery surrounding the classic wave theory?
Classic wave theory attributed the photoelectric effect to light energy being transferred to the electron. According to this theory, if the wavelength of light is made shorter or the light waves intensity made brighter, more electrons should be ejected.
H
Photons (explanation of photoelectric effect)
Einstein proposed:
that light energy is delivered to atoms in packets called quanta or photons
The energy of a photon of light is directly proportional to its frequency and inversely proportional to its wavelength
The proportionality constant is called pl
planck's constant
h on equation sheet
Energy of photon using planck's constant (on eq sheet)
Energy = planck's constant
frequency = [(planck's constant)
(speed of light)] / wavelength
Energy of photon using binding energy and kinetic energy (on eq. sheet)
1 photon at the threshold frequency has just enough energy for an electron to escape the atom. This is the binding energy, BE.
For higher frequencies, the electron absorbs more energy than is necessary to escape. This excess energy becomes kinetic energy
Bohr's model of the atom
1. e- can only have specific (quantized) energy values, OR only orbits of certain radii, corresponding to certain specific energy levels, are permitted for the electron in an element's atom.
2. Light is emitted as e- moves from one energy level to a lower
Energy of photon using principal quantum numbers and rydberg's constant (only works for hydrogen!)
Energy of final level = -Rh (1/n(final)^2)
Energy of initial level = -Rh (1/n(initial)^2)
On eq sheet: Energy of photon = (delta)E
= Rh [ (1/n(initial)^2) - (1/n(final)^2) ]
When the electron falls to a lower energy level, the value will be negative becau
Rules for electrons and atomic emission spectrums
1. Electrons only emit light at discrete wavelengths
2. Each specific wavelength corresponds to a specific energy. For hydrogen (On eq sheet): Energy = [(Planck's constant)*(Speed of light)] / wavelength
3. Electrons must only make transitions between dis
quantum-mechanical model
Explains the manner in which electrons exist and behave in atoms; helps understand and predict atom properties as they relate to electron behavior
Wave behavior of electrons
de Brogile proposed that particles could have wave-like characteristics
Because electrons are so small, the wave character is significant
He predicted that the wavelength of a particle was inversely proportional to its momentum
On eq sheet: wavelength = p
momentum
Mass x Velocity
Uncertainty principle
The product of the uncertainties in both the position and speed of a particle are inversely proportional to its mass.
This means the more accurately you know the position of a small particle, like an electron, the less you know about its speed and vice ve
what does Schrodinger's wave equation describe?
1. energy of an electron with given wave function value
2. probability of finding an electron in a volume of space
psi greek
symbol used for the wave equation
what does a graph of the wave function look like?
Orbital shapes
orbital
region in space where electron is more likely to be found
variables in wave function (quantum numbers)
Principle quantum number (n): distance from nucleus
Angular-momentum quantum number (l): shape of orbital
Magnetic quantum number (m sub l) : orientation in space
Spin quantum number (m sub s) (not really a variable): direction of electron spin
Allowed quantum numbers
n: 1, 2, 3, ...
l: 0,1, 2, 3 .... n-1 (number of values = n)
m sub l: -l,....0.....,+l (number of values = 2l+l)
m sub s: -1/2 or +1/2 (number of values = 2)
shell
each value of n (principle quantum number) is called a shell.
subshell
l (angular momentum quantum number) corresponds to a subshell
subshells
l = 0 s orbital
l = 1 p orbital
l = 2 d orbital
l = 3 f orbital
S orbital
each principal energy state (n) has 1 S orbital
S orbital is the lowest energy orbital in a principal energy state
spherical
number of nodes = (n-1)
2 electrons
nodes
point where electron probability is 0
p orbital
each principal energy level above n = 1 has 3 p orbitals (m sub l = -1, 0, 1)
each of the 3 orbitals point along a different axis
2nd lowest energy orbitals in the principal energy state
two-lobed
nodes at the nucleus, total of n nodes
6 electrons
d orbital
each each principal energy state above n = 2 has 5 d orbitals (m sub l = -2, -1, 0, 1, 2)
4 of the 5 orbitals are aligned in a different plane while the fifth is aligned with the z axis
3rd lowest energy orbitals in a principal energy state
mainly 4-lobed
f orbital
each principal energy state above n = 3 has 7 d orbitals (m sub l = -3, -2, -1, 0, 1, 2, 3)
4th lowest energy orbitals in a principal energy state
mainly 8-lobed
planar nodes
14 electrons
m sub l corresponds to...
the number of different orbitals in a subshell
pauli exclusion principle
no two electrons in the same atom can have the same set of four quantum numbers
which means
An atomic orbital may describe at most two electrons, each with opposite spin direction
energy of orbitals in a single electron atom...
only depend on n
energy of orbitals in a multi-electron atom...
depend on n and l
s block, p block, etc on periodic table (with number reminders for d and f)
draw and refer to lecture slides
Aufbau building up priciples
1. lower energy orbitals fill first
2. each orbital holds two electrons; each with different m sub s (spin)
3. half fill degenerate orbitals (orbitals that have the same energy) before pairing electrons
electron configuration configuration
n(letter l corresponds to)^number of electrons in orbital or subshell
orbital filling diagram
electrons are arrows (arrows are different directions to represent different spin)
valance electrons
the electrons in all the subshells with the highest principal quantum number
core electrons
electrons in energy shells lower than the valance electrons
core notation
a method of writing an electron configuration in which core electrons are represented by a noble gas symbol in brackets followed by the valence electrons for example (NE) 3s2
full d or f sub shells in main group elements are...
not considered valance electrons
full f sub shells in main group elements are...
not considered valance electrons
Viable wavelengths
400-700 nm
Hund's rule and what it means for orbital filling diagrams
The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins. This mean orbitals degenerate orbitals will fill with arrows going in the same direction first
periodic table and valance electrons, quantum number, and electrons in subshells
in groups 1-8A, the number 1-8 indicates the number of valance electrons in the atom of an element in that column
the row number indicates the quantum number (with d being 1 less than s and f being 2 less than s)
the number of columns over you are in the
anomalous electrons configurations
Chromium should be [Ar] 4s^23d^4 but is actually [Ar] 4s^1 3d^5
Copper should be [Ar] 4s^2 3d^9 but is [Ar] 4s^1 3d^10
It makes sense that these are happening in the 4th and 9th columns
This occurs because it is more stable to have half-filled and full-fi
paramagnetic
elements which have unpaired electrons and are affected by magnetic fields. The more unpaired electrons, the more magnetic.
diamagnetic
elements which have all electrons paired and are unaffected by magnetic fields
Toroid
Donut shape in electron orbitals d and f