CHEMISTRY OF ART
Light emission by Atoms
COLOURS & FIRES
•
Stage 6 Chemistry Syllabus – Chemistry of Art (Option)
•
Identify Na+, K+, Ca2+, Ba2+, Sr2+, and Cu2+ by their flame colour
•
Perform first-hand investigations to observe the flame colour of Na+, K+, Ca2+, Ba2+,
Sr2+, and Cu2+ (Demo only this lesson)
•
Explain the flame colour in terms of electrons releasing energy as they move to a lower
energy level
•
Explain why excited atoms only emit certain frequencies of radiation
•
Explain what is meant by n, the principal quantum number
•
Identify that, as electrons return to lower energy levels, they emit quanta of energy which
humans may detect as a specific colour
WHAT’RE THOSE COLOURS?
.
•
The colours of all glowing substances have the same starting point
•
They come from atoms and molecules that have been excited to states of energy.
•
Atoms in burning fireworks and stars have become excited by absorbing energy as heat;
then convert that energy into coloured light which is emitted.
•
The colours shown by an atom depend on how it’s electrons are configured.
•
Thus, by investigating the colours an atoms of an element emit, we can determine its
atomic structure and work out which element it is.
ACTIVITY 1
ACTIVITY 2
Specific metal ions are used in fireworks to show different colours
Metal ions can be identified by the unique colours of their flames.
ACTIVITY 2
Specific metal ions are used in fireworks to show different colours
Metal ions can be identified by the unique colours of their flames.
HOW ARE THESE COLOURS EMITTED AT AN
ATOMIC LEVEL?
Meetal Kumar
ATOMIC EMISSION SPECTRA in the
ELECTROMAGNETIC SPECTRUM
Electromagnetic
spectrum: range
of all wavelengths
of electromagnetic
radiation
Atomic Emission
Spectra: Set of
wavelengths of
the
electromagnetic
spectrum emitted
by excited
electrons of an
atom
What happens when white light passes through a prism?
Instructions:
1) Turn on the ray box
2)
Place the prism flat on the
paper in front of the ray box
so that the beam of light
passes through it
3)
Turn off the lights
4)
Observe the beam of light as
it enters and exits the prism
What do u see?
WHAT HAPPENS WHEN WHITE LIGHT PASSES
THROUGH A PRISM?
The light is separated and dispersed into the full visible
spectrum
FOR EXAMPLE:
•
Sunlight passes through a raindrop the light is dispersed into a visible rainbow
QUESTION
•
What happens when we hold a prism in front of light emitted from these specific
burning elements? Would we see the entire visible spectrum?
•
A: Yes, we would see the entire visible spectrum
•
B: No, we would see bands of light broken up
•
C: No, we would see the colours refracting back into its white light form
•
Answer:
•
B: No, we would see bands of light broken up
For example, Na+ light is broken up into bands within the spectrum
- Notice each element has a unique spectrum that is emitted, referred to as its
‘Fingerprint’ and allows us to determine which element is becoming excited
FIRST LETS LOOK AT THE ELECTRON
CONFIGURATION OF AN ATOM
•
Quantum numbers = energies of electrons in atoms or ‘shells’
•
They are like the ‘address’ of the electron
•
No two electrons can occupy the same address
•
N is called Principal energy level
•
It is always a whole number
QUESTION:
•
If these energy levels or ‘shells’ are not occupied by electrons, are the shells still present?
Yes or no?
•
Answer:
•
YES! The energy levels are always present
HOW DO FLAME TESTS WORK
WHAT CAUSES THE ELECTRON TO BECOME
EXCITED?
•
1) Electron begins in Ground State (electron in n=1)
•
2) Energy eg. heat is absorbed by electron
•
3) Electron bounces to higher energy level  enters
Excited State (eg N=2,3,4)
•
4) Electron releases Photon (light energy) 
moves back down to lower level energy
•
N=1 – UV rays ( not visible)
•
N=2 – Visible
•
N=3+ - IR rays (not visible)
HOW DO FLAME TESTS WORK
•
Using all this information allows us to observe colours emitted from fireworks or outer
space for example and determine which elements are becoming excited and emitting
that colour of light
EMISSION SPECTRA
Pembe Hussain
MARS
Dark red
patches
Pale yellow
patches
CHEMICAL COMPOSITION OF MARS
Iron oxide and
small traces of
calcium
Pale
yellow/white
patches =
hydrogen,
helium, sulfur
and sodium.
JUPITER
Pale grey
Orange
JUPITER’S COMPOSITION
Hydrogen,
helium with
ammonium
Phosurphous,
sulfur and
hydrocarbons
SUN WHEN IN SPACE
Naturally
white with
slight blue
tinge
SUN WHEN IN SPACE
Helium
and
hydrogen
COLOUR OF THE SUN WHEN IT IS UP DURING THE DAY
SUN WHEN IN SPACE
Helium
and
hydrogen
No interfering wavelengths
SO WHAT ARE WE TALKING
ABOUT?
VISIBLE LIGHT
The only electromagnetic waves detectable by
human eyes
WHAT IS A WAVELENGTH?
• It is from one “bump” to another.
• The technical term for a “bump” is a crest 
Each colour has its own wavelength that sets it
apart so we can see it
WITHIN THE VISIBLE LIGHT SECTION, WE HAVE A
BREAK DOWN OF COLOURS
so that
means:
Visible
light has
its own
spectrum`
RIDDLE:
What does a fingerprint
belonging to a human
being, and the electron
configuration of an
element have in
common???
They are both unique to the individual and
element
Different electron configurations
Different electrons being excited @ different energy
levels (n)
different photons released
different wavelengths
VISIBLE
WAVELENGTH AND COLOUR
SO: EACH ELEMENT HAS ITS OWN UNIQUE
QUESTION:
Does an element emits only one
colour?
Yes and no.
We see only one colour but,
as electrons travel between
different energy levels, they
release different photons
and wavelengths. We just
see the most dominant
wavelength.
POTASSIUM - K+
• Flame colour is lilac
• YET:
the potassium wavelength is a mixture of red @650 nm and blue
@475 nm.
4000 A
o
5000
6000
7000
An atom actually emits all of the colours, but the only
colour detected by the human eye is that wavelength most
dominant in the emission spectrum
SO….
Potassium when heated emits a lilac flame because:
It is the dominant
wavelength
4000 A
o
5000
6000
7000
EMISSION SPECTRUM
shows the electron configuration of a specific atom
EACH EMISSION SPECTRUM IS UNIQUE TO ON
PARTICULAR ELEMENT
4000 A
o
5000
6000
• Why?
Because it is like a finger print
7000
APPLICATIONS:
• Identify different chemicals in a solution/substance
for art restoration and chemical analysis
• Fireworks
• Astronomers use telescopes with detection
devices that are sensitive to wavelengths
 Determine composition
FLAME TEST COLOURS
Sodium, Na
Calcium, Ca
NEXT LESSON:
• You will perform a first-hand investigation
into observing the flame colours. You will be
given unknown solutions and from this
lesson, you will be expected to indentify
them.
FIREWORKS
FIREWORKS
HOW DO FLAME TESTS WORK