Quantum Theory
Structure of an atom
What we are going to learn this chapter
Properties of waves and
electromagnetism
Bohr’s theory of a hydrogen
atom and its relation to
emission lines
Debroglie wavelengths
Quantum numbers
Electron distribution
Electron configurations
Many important theories and
principles
Plank’s quantum theory
Einstein’s photoelectric
effect
Heisenberg uncertainty
principle
Schrodinger wave
equation
The Birth of Quantum Mechanics
Before 1900 atoms and molecules were
regarded as rebounding balls.
This is the basis of theories such as the
ideal gas law and works well to describe
macroscopic phenomena
After 1900 Max Planck (nobel prize
1918) discovered that atoms or
molecules only emit energy in discrete
levels or “quanta”
Energy was NOT continuous and this
turned physics upside down.
We have no right to assume that
any physical laws exist, or if they
have existed up to now, that will
continue to exist in a similar
manner in the future.
-Max Planck
Development of Atomic Models
Thomson: The plum
pudding model
postively charged jellylike
blob, with suspended electrons
Rutherford: nuclear model
all positive charge in the nucleus
negative charge surrounding it:
Bohr model: expansion of
Rutherford’s ideas.
Electromagnetic radiation
Electromagnetic radiation is a
form of energy. That has
wavelike properties.
Heat
microwaves
xrays
What Else?
sunlight
Properties of Waves
Examples of Transverse Waves
Examples of Longitudinal Waves
Transverse waves- Frequency
Frequency (ν) (pronounced nu) is equal to the
_______________________________________
In equation form ν=c/λ
Units of ν is _____________(pronounced ______)
Units of λ is distance, visible light is around nm
(nanometers)
Electromagnetic Waves
Electromagnetic waves
have and electric
component and a magnetic
component
Two components have
same wavelength and
frequency, in
perpendicular planes
http://hyperphysics.phy-astr.gsu.edu/
Be sure you can identify:
Amplitude
Wavelength (λ)
Frequency
Travel at 2.9989x108m/s
(the speed of light c)
Electromagnetic Spectrum
As wavelength increases
what happens to frequency?
does it:
A) Increase
B) Decrease
Decrease
Answer the Following:
Which has greater frequency red light or blue light?
Which has greater energy?
Blue
Blue
Does blue light have greater speed than red light? NO! all have same speed
Example Exercise
The wavelength of green light from a traffic signal is centered at
522 nm. What is the frequency of this radiation.
Known:
c= 3.00x108m/s
λ=522 nm
ν=c/λ
Then fill into equation
First convert λ to meters
Fix sig figs and check for units
Another Example
The frequency of radiation from your microwave is 120 GHz. Find the
wavelength of the microwaves.
Similar at home exercise: The wavelength of radiation when you get an
xray is 10.0 nm. Find the wavelength of the xrays.
In Class Quiz
The frequency of red light from a traffic signal is centered at
4.11x1014Hz. What is the wavelength of this radiation?
A) 1.37x106 m
B) 1.37x106 nm
C) 730 nm
D) 7.30x10-7nm
Planck’s Quantum Theory
When solids are heated they emit
__________
Attempts to explain this up until Plank
failed at either very high or low
wavelengths.
Planck discovered molecules can only emit
light at specialized energies or “_________”
A “__________” is the smallest quantity of
energy and is equal to:
h=6.626x10-34 J*s
Example Exercise
What is the energy of green traffic light in the previous
example. (λ=522nm)
Known:
c= 3.00x10-8m/s
λ=522 nm=5.22x10-7m
Another Example
The frequency of radiation from your microwave is 120 GHz. Find the
energy of the microwaves.
To do at home:
The wavelength of red light from a traffic signal is centered at 730 nm.
What is the energy of this radiation.
The frequency of radiation of an xray is 3x1016 Hz. Find the energy of the xrays.
Black Body Radiation
Blackbody radiation
depends only on
temperature of object
Given this information about a light
bulb, why are incandescent bulbs
inefficient light sources?
2700-3300K
Example Exercise
What is the wavelength of the brightest part of the light from
our next closest star, Proxima Centauri? Proxima Centauri is a
red dwarf star about 4.2 light years away from us with an average
surface temperature of 3,042 Kelvin.
Light: A wave or a particle.
Wave
Both
~300B.C
Aristotle
~1600 A.D.
R. Descartes
~400B.C
~1000 A.D.
Democritus Alhazen
~1700 A.D.
Robert Hooke
~1700 A.D.
Sir Isaac Newton
~1800 A.D.
Thomas Young
~1700 A.D.
C. Huygens
Albert Einstein
~1900
Particle
Photoelectric Effect
Ejection of _________ from the
surface of a metal or other material
when shines on it.
Energy of _______________must be
higher than “_______” energy or no
photon will be ejected. This
________________is called the
“________________”
Ex: Violet light can eject electrons from
potassium, but red light can’t.
Use E=hν to determine threshold
frequency.
Shows _______________________
http://phet.colorado.edu/en/simulation/photoelectric
Photoelectric Effect
What do you think happens
if the intensity of light is
increased but the frequency
of the electrons stay the
same?
If the photon is exactly the energy of the work function
the electrons will be knocked loose
If the energy of the photon is higher the electrons will
acquire _________________________
_________________________
Photoelectric effect example problem
The work function for calcium is 4.34x10-19 J. What is the minimum frequency of light
for the photoelectric effect for calcium. Then calculate the kinetic energy of the ejected
electron if the light of frequency 1.00x1015 s-1 is used for irradiating the metal.
Photoelectric Effect: A second look at the equation
Ek=hν - Φ
y= mx + b
Before threshold frequency ___________________is present
After threshold frequency the relationship is _____________
Photo Electric Effect Extra Notes:
Rephrasing of what I said just for you
The idea here is that given one photon you are
transferring that energy into the electrons in the metal.
If you put exactly the amount of energy in it needed to
eject an electron (aka the work function, aka Φ or W)
then there is no energy left over for it to move (aka
have kinetic energy)
However if the photon has more energy than the work
function, it transfers that in the form of movement
(aka kinetic energy)
You Try Similar at home
Exercise:
You Try: The work function for magnesium is 5.9x10-19J. Calculate the minimum frequency
of light required to eject electrons from magnesium. Then calculate the kinetic energy of
the ejected electron if the light of frequency 1.00x1015 s-1 is used for irradiating the metal
Wave Interference
Constructive
Waves with same
phase interfere
________________
They ______
Waves with different
phase interfere
________________
They _________
Destructive
Double Split Experiment: Young
Wave or Particle?
Summary: Experiments show it has properties of both.
Photo electric effect:
Particle like
Double split experiment
wavelike
This is true of very small matter
Largest so far to have measurable wave-like properties is those with
mass 1610 amu
DeBroglie Wavelength: Describing
matter as a wave.
De Broglie expanded wave particle duality from light to
matter.
Here
is equal to the
velocity of the particle, not
the frequency.
Often you’ll find the velocity using
the kinetic energy.
Example Problems: DeBroglie Wavelength
Find the DeBroglie wavelength of an electron with a K.E. of 2.56x1027J.
Why can’t we see the waves of macroscopic matter?
(hint :A baseball weights 0.145kg and it moves around 27 m/s.)
Heisenberg Uncertainty
Principle
It is impossible to know simultaneously both the momentum
(p) and the position (x) of a particle with certainty.
The uncertainty values are related by:
(momentum=mass*velocity)
If your uncertainty of momentum decreases your
measurements of position will _______________ and vice
versa.
What happens to the uncertainty in position if your
uncertainty in velocity decreases?
Heisenburg Uncertainty Principle Examples:
You are pulled over by a police officer for speeding,
and try to escape a ticket by claiming if he knew where
you are, he can’t possibly know how fast you were
going. The officer says, “well, I knew where you were
within 0.5 m, your car probably weighs around 1300kg,
so I know your velocity within…….”
Wavefunctions, Energy levels, and particles in a box
Ψ Is the “______________”
Describes the __________________.
Its just a symbol for a mathematical
function
Different particles have different
wavefunctions
Ψ2 is the “_______________”
The probability of finding the
________________________
Technically “__________________”
probability of finding a particle divided by
the volume.
Wavefunctions, Energy levels, and particles in a box
Some questions for you.
Ψ is a function, so at any point can we absolutely determine the
sign. Is itAlways Positive
Always Negative
Can be both
Ψ2 Is the square of that function so can we absolutely
determine the sign. Is itAlways Positive
Always Negative
Can be both
Nodes
A node occurs when Ψ is
_____
When this happens, what is
Ψ2 equal to?
__________
So what is the probability
that the electron is at a
node?
_____________
Number of nodes is equal to
n-1
Um….what was that again:An example.
Lets take an example where Ψ is a
number (to make it simple). We’ll say
0.44cm-3
So then Ψ2=0.20cm-3.
Ψ
So the wavefunction is equal to
0.44cm-3
Ψ2
and the probability density is equal to
0.20cm-3 .
What is the probability of finding the
particle within 3cm3?
0.2cm-3 * 3cm3=0.6 or 60%
0cm3
3cm3
X
Schrödinger Equation
The “hat” on the H indicates it’s an ____________.
Can use to find _________________
We will use the results of this, not the actual equation.
Particle in a Box.
Set up: A single particle is in
a box.
Only certain
______________ are
allowed.
Energy is “__________”
Real life relation: String
anchored at two points.
Particle in a Box: Solutions
Solution to Shrodinger equation:
L is the ______________.
n is the _______________
it is an integer.
Particle in a Box Example:
Use the solutions to the Schrödinger equation for a
particle in a box to estimate the value of the
wavelength of an electron in a helium atom given that
the approximate radius of a helium atom is 100. pm.
Bohr model of the atom
Before this arose they knew there
were electrons traveling around a
proton filled nucleus.
Laws of physics said electrons
should spiral into nucleus.
Bohr said energy levels are
________________
Only works for _____________
Energy difference is given by:
Rh=2.18x10-18J
n= 1,2,3……
“_________________________”.
Energy levels
Z=atomic number
A Hydrogen Atom
Two different ways of thinking about it.
Rydberg equation
Was discovered by analyzing line spectra
Schrodinger equation
Solving the particle in a box problem in three
dimensions
Same results from either equation.
Rydberg’s was determined first, then Shrodinger’s results
agreed.
Also true for “hydrogen-like” atoms.
1 electron atoms.
We’ll start with Schrödinger
Results from solving the
Shrodinger equation for the
hydrogen atom
Z is the atomic number
me is the mass of an electron
e is the charge of an electron
or proton
h is Planks constant
r is atomic radius
Agrees with experimental
results
Stair and Ball Analogy
Bohr Model Energy Levels
The energy of a given energy level is given as:
• So the difference in energy is
Rydberg Equation
If the energy of a given energy level is defined as En=-Rh(1/n2).
We can find the difference in energy shells by Enf-Eni
Change=
__________________
__________________________
Filling the above equations
into Change= Final-initial
…and finally rearranging
Either of these are often shown in text
books. Use whichever you prefer but be
sure not to mix them up. One has a
negative one does not.
Rydberg's constant is experimental value
Sign Conventions for Energy:
*common error causes*
A free electron has ΔE=
ΔE is +
Energy of levels are negative, most negative and
therefore lowest energy is n=1
ΔE is positive if going from ___________ energy
shell i.e. ground state to anything, 25 ect…
Words such as “photon absorbed” will be used.
ΔE is negative if going from _____________ i.e.
anything to ground state, 52 ect… Words such as
“photon emitted” will be used.
E=hν=hc/λ This energy is the energy of
__________________. This must always be
______________!
ΔE is -
Example Problems Rydberg Equation
A photon that is emitted when a hydrogen undergoes a transition to
n=2 is of the frequency 6.17x1014 s-1. Find the initial energy level.
What is the wavelength of a photon emitted during a transition from
the n=5 to n=2 state in a hydrogen atom?
Lasers
Light Amplification by Stimulated
Emission of Radiation.
http://www.infoplease.com/images/ESCI112LASERS003.gif
Example Problem Rydberg Equation
A monochromatic beam of light with a total energy of 2.5J contains
8.56x10-4 mols of photons. What is the wavelength of the beam.
Emission Series
Emission Series: Another
Look (Hydrogen)
What do we use Emission Spectra for?
Emission Spectra is unique to individual elements
Spectra can be collected and matched to known emission spectra
to determine the element present.
Flame tests
Hydrogen Emission Spectra
Fe Emission Spectra
Flame test
Emission/Absorption Spectra
Lines in visible region
shown above (Hydrogen
shown)
Also some occur in other
spectral regions and
aren’t seen without
detectors
Emission Spectra: Applications in Astronomy
•Spectra is collected
•Compared to known ions
•Temperatures known
Time to regress to our 5 yr old selves
Why is the grass
green?
Why is the sky blue?
Why is the sun
yellow?
The grass is green because…
What happens if you shine green
light on the plants?
What happens if you shine red
light on the plants?
Why is the Sky Blue?
Previous Slide Lecture Summary
Long wavelength Red and orange light travels
relatively unperturbed through the atmosphere.
Shorter wavelengths get scattered turning the sky
blue. As it travels farther much of the blue light
interferes with each other cancelling each other
out and making the sky paler.
During sunset the light has to travel so far
through the atmosphere that most of the blue
light is completely scattered and interfered away.
Leaving only the reds/oranges and yellows to
reach your eyes.
Other Transitions
Schrodinger Equation
Eψ=Hψ
Ψ is the “__________”- complex function of space and time.
Describes particle.
Ψ ____________________
|Ψ2| is the “_____________________”
These probability densities make up “____________” which
describe
______________________________________________.
Technically this is only good for one electron atoms but there
are good approximations for many electron systems.
Atomic Orbitals
Exact solutions to the Schrödinger equation for
hydrogen like atoms
Approximate solutions to the Schrodinger equation for
atoms with more than one electron.
Shows where the ______________________________.
Technically extend to infinity, normally drawn where
there is a 90% probability of finding the electron
Atomic Orbitals
Wavefunctions
s
1s
2s
px
1p
py
3s
pz
3p
dxy
3d
dyz
dzx
dx2-y2
dy2
You don’t need to know these wavefunction equations, won’t need to use them. Just FYI so you
know what they look like.
Quantum Numbers
Describes the distribution of electrons.
The combination of them all specifies the wavefunction.
You can think of it as an address to an electron
Analogy: Finding Person on
Campus
Building number 403
Room number 1100
Row F
Chair 1
Male or Female
Quantum
numbers
n
l
ml
ms
Quantum Number- Principle
Quantum Number
______________________- “n”
Can have any positive integer.
We saw this in the ____________ as the energy
levels. 1,2,3….∞
Quantum Number- Angular Momentum Quantum Number
Angular Momentum Quantum Number- “l”
Distinguishes the orbitals of different shape.
Values have letters associated with them.
0=s, 1=p, 2=d, 3=f, 4=g,…….. These are associated with the atomic
orbitals we just discussed.
Can be any integer from 0 to n-1.
n
1
2
3
4
allowed values of
l
Question: For the 4th energy
shell, what are the orbitals
present?
Quantum Numbers- Magnetic Quantum Number
Magnetic Quantum number- “ml” (read as m sub l)
Distinguishes orbitals that have same n and l (same energy
and shape) but having a different orientation.
Allowed values are from –l…0…l
Table of Allowed Values for 1-4 energy levels
n
1
2
3
4
l
ml
Lets fill in the numbers
for the n=3 energy level.
Quantum numbers
s
l=0
ml=0
p
l=1
ml=
-1
0
1
l=2
ml=
2
-1
0
1
2
d
***The quantum numbers ml here doesn’t necessarily relate to the exact orbital its under, don’t
worry about memorizing which goes where.
Wavefunctions
s
1s
2s
px
1p
py
3s
pz
3p
dxy
3d
dyz
dzx
dx2-y2
dy2
You don’t need to know these wavefunctions equations, won’t need to use them. Just FYI so you
know what they look like.
Quantum numbers- spin quantum number
Spin quantum number- “ms” (read this as m sub s)
Distinguishes spin axis of electron. (also shown as spin up or spin
down on diagrams)
Allowed values for each orbital are +1/2 or -1/2.
Question- How many electrons are allowed per individual orbital?
State whether each of the sets of quantum numbers
is permissible for an electron, if not explain why.
Example 1: n=1, l=1, ml=0, ms=+1/2
Example 2: n=3, l=1, ml=-2, ms=-1/2
Example 3: n=2, l=1, ml=0, ms=+1
Example 4: n=3, l=2, ml=-2, ms=-1/2
Shielding and Penetration
Orbitals with radial
probability closer to the
nucleus are more
penetrating.
The closer, more
penetrating orbitals are
shielding the further
orbitals from the
nucleus.
Energies of Orbitals
Hydrogen
Everything other than Hydrogen
Ect….to infinity
Ect….to infinity
E
Questions: What is the difference between the two? Why do you think
hydrogen is different?
Here I have draw hydrogen with atomic orbitals higher than 1. Is this
correct? Why or why not?
Energies in Relation to Periodic Table
Electron Configuration
Pauli Exclusion Principle states that
no two electrons can have all four
quantum numbers be the same.
Fill in electrons in order of energy
levels.
Each orbital holds 2 electrons.
Right
Diagram for Carbon
Hund’s rule- Fill across degenerate
energy levels before filling orbital.
Write electron configuration as
follows: 1s22s22p2
Example:
Write electron configuration for Cobalt
Diamagnetism vs
Paramagnetism
______________ has
unpaired electrons
Carbon
Drawn Toward magnets
_____________ has paired
electrons.
Slightly Repelled by magnets
Neon
Electron configurations of ions
Simply add or subtract
electrons based on the
charge of the ion
Example: Ca to Ca2+
Ca
1s22s22p63s23p64s2 or ___________
Electron configurations of ions
Simply add or subtract
electrons based on the
charge of the ion
Example:Ca to Ca2+
Ca2+
1s22s22p63s23p6 or ________________
_________________
Electron configurations of ions
Simply add or subtract
electrons based on the
charge of the ion
Example:Cl to Cl1-
Cl
1s22s22p63s23p5 or [Ne] 3s23p5
_________________
Electron configurations of ions
Simply add or subtract
electrons based on the
charge of the ion
Example:Cl to Cl1-
Cl-
_________________
Electron Configurations
Exceptions
Half filled and full filled orbitals are more stable. To get d
orbitals to this stability promote electrons from s orbitals
When valence d orbitals have electrons and you need to make
an positive ion, remove from valence s orbitals first.
Fs also have a bunch of exceptions, don’t worry about these. If
I ask for an electron configuration from the F block, just
follow the rules
Question: Why can we be so fluid with our exchange of
electrons from the s and d orbitals?
Electron configurations of ions
Simply add or subtract
electrons based on the
charge of the ion
Example: Co to Co2+
Co
1s22s22p63s23p64s23d7 or ____________
Take away two electrons
Where are we taking them
from?
Electron configurations of ions
add or subtract electrons
based on the charge of the
ion
Example: Co to Co2+
Co2+
1s22s22p63s23p63d7 or [Ar] 3d7
Take away two electrons
_________________
Electron configurations of ions
Example:Cr to Cr1+
Electron configuration of
neutral chromium
requires promotion of
electron
Cr
To give stable half shell
Electron configurations of ions
Example:Cr to Cr1+
Electron configuration of
neutral chromium
requires promotion of
electron to give stable half
shell
Cr
1s22s22p63s23p64s13d5 or _____________
Then take away electron
from 4s shell
Electron configurations of ions
Example:Cr to Cr1+
Electron configuration of
neutral chromium
requires promotion of
electron to give stable half
shell
Cr1+
1s22s22p63s23p63d5 or _____________
Then take away electron
from 4s shell
You Try
Use what we just learned about Chromium to write the
electron configuration of Cu and Cu1+.
Electron configurations of ions
Example:Cu to Cu1+
Electron configuration of
neutral copper requires
promotion of electron to
give stable full shell
Cu
Then take away electron
from 4s shell
Electron configurations of ions
Example:Cu to Cu1+
Electron configuration of
neutral copper requires
promotion of electron to
give stable half shell
Cu1+
Then take away electron
from 4s shell
Discussion Question
Using the logic we just worked out why do Cr, Mo, W,
Cu, Ag and Au all form +1 ions?
Switching Gears….. Periodic Trends
Atomic Radius
Ionic Radius
Ionization Energy
Electron Affinity
What we are going to learn!
Some history about the periodic table development
Trends: using the periodic table to predict
Ionization energy, electron affinity, atomic radius,
effective nuclear charge and electro negativity.
Instead of 1.21, directly, we’ll just talk about some
interesting elements.
Development of the Periodic Table
Electronegativity
Electronegativity
Effective Nuclear Charge
Effective Nuclear Charge
Increases __________________
Vertical Trend doesn’t make a lot of sense to discuss
here so we will ignore it
Nuclear charge felt by an electron when both the actual
_____________________and the _______________
of other electrons are taken into account.
Core electrons shield the ______________.
Reason behind many of the other trends!
Atomic Radius
Increases down a group
Increasing amount of ___________ increases size.
Increases right to left across a period
Due to ________________________________,
holds electrons closer
Examples
Rank the following in order of increasing radius
Li, C, F
Li, K, Rb
Ba, Se, F
Would you be asked to rank, Be, Al, Ge? Or similar?
Ionic Radius
Cations are smaller
More positive is smaller. _____ is smaller than ______
Anions are bigger
More negative is bigger. _____is larger than ______
Higher effective nuclear charge when electrons are
removed, lower when electrons are added.
Example:
S2-,
Draw an arrow from the smallest to largest
species in the following isolectronic series
Cl-,
Ar, K+,
Ca2+
First: what is this “isoelectronic” word
iso=_________
electronic: sounds sort of like electron
so……
isoelectronic= ___________________
More examples
Rank the following in order
from smallest to largest:
Li+, Be2+, F-
Cu+, Cu2+, K+
Cl-, F-, Br-
and another:
Given the following pictures of ionic compounds match the
pictures with the ions: Na+, Mg2+, Cl-, O2-
Pink
Purple
Blue
Green
First Ionization Energy
Minimum energy required to remove an electron from its ground state
General Trends with exceptions
Exceptions come from getting
half and fully filled subshells:
You need to know these!
What is the electron configuration of Be, B, N, O?
Use this to explain the higher ionization energy.
F
N
Cl
O
Be C
P
Mg
B
S
Al
Be:
N:
B:
O:
Examples:
Rank the following in order from lowest
to highest first ionization energy.
First some normal ones
He, Ne, Ar
Now some exceptions:
Li, Be, B
C, N, O
B, Li, Ne
Second and Third Ionization Energy
First is always the
_________.
2nd
1st
3rd
Nuclear charge**
doesn’t change, so
each electron feels
more of a positive pull.
**Notice this says nuclear charge, not effective nuclear charge
e
eg.
Electron Affinity
Cl +
e

Cl
Electron Affinity
General trends, but has a fair amount of exceptions
Lets look at some values
Positive electron affinities means its exothermic
Electron Affinity
Why do group 2A (alkaline earth) an 7A (halogens) form stable
atomic anions? (aka -1 ions)
High effective nuclear charge means ______________.
One more electron fills the shell, this adds __________
F:
F-:
Na:
Na-:
Filled sub-shells are stable.
Why do the noble gasses and not form stable atomic anions?
Ne: 1s22s22p6
Already has a filled shell. Already stable,
adding an electron isn’t energetically favor.
N: 1s22s22p3
Have a filled half shell, adding another electron
causes ______________________________.
Electronegativity (Chapter 2.12)
Ability of an atom to attract electrons
_______________________________________________
Not as many important exceptions, mostly involving the d
block. We won’t worry about them.
Why aren’t there as many exceptions with these?
Electronegativity and Electron affinity
O atoms are electronegative
Same general trend
Both involve ability of an atom
to _______________
CO2
Electronegativity is that ability
while _________, attracts
shared ______________
e-
Electron affinity is that ability
of an _______________.
eg.
Cl + e- 
high electron affinity
Cl-
Inert Pair Effect
Tendency of heavier atoms to form ions with a difference in charge of two.
Use electron configurations to explain.
Sb
Sb:
Sb3+:
Sb5+:
Pb
Pb:
Pb2+:
Pb4+:
Do the rest at home for practice!
Diagonal Relationship
Diagonal bands going down and
right have similar properties.
Look at radii and ionization
energies and explain.
General Trends in Chemical Properties
Understand why the groups in general form certain
ions.
Understand why trends occur including reactivity in
section 1.21
What follows is a smatterering of interesting aspects
of elements I think is pertinent to real life.
Silicone as a basis for life?
Smallest element with same valence
electron structure as carbon
Many similar properties to carbon
Probably not as likely as SciFi makes it
out to be
Doesn’t bind with as many atoms
Doesn’t make double or triple bonds,
severely limiting chemistry
Si chains with H are unstable in water.
Si chains with O are more stable, but still
not as stable as carbon.
Noble Gases
He: refrigerant for super conducting magnets like in
MRIs: used in scuba diving and blimbs.
Many uses where you need an “inert” atmosphere,
chemistry, lightbulbs, storage ect…..
“Neon” lights, which are really many elements.
Interesting tidbit: Argon means “the lazy one” in greek.
He
Ne
Ar
Kr
Xe