Download electromagnetic spectrum and flame tests

ELECTROMAGNETIC SPECTRUM
AND FLAME TESTS
Agenda
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Day 13 - Flame Test Lesson:
Lesson: PPT,
Handouts: 1.PPT Handout;
Text: 1. P. 20; 439-440- Qualitative Analysis
Involving Colours
• HW: 1. P.441 # 5,6,9; 2. Finish all the
worksheets
Flame Test Demo- Pg. 439
Compound
Lithium chloride
Potassium chloride
Copper (II) chloride
Cation
Li+
K+
Cu2+
Sodium chloride
Strontium chloride
Na+
Sr2+
Colour
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Flame Test Colors
Symbol
Element
As
Arsenic
B
Boron
Ba
Barium
Ca
Calcium
Cs
Cesium
Cu(I)
Copper(I)
Cu(II)
Copper(II)
Cu(II)
Copper(II)
Fe
Iron
In
Indium
K
Potassium
Li
Lithium
Mg
Magnesium
Mn(II)
Manganese(II)
Mo
Molybdenum
Na
Sodium
P
Phosphorus
Pb
Lead
Rb
Rubidium
Sb
Antimony
Se
Selenium
Sr
Strontium
Te
Tellurium
Tl
Thallium
Zn
Zinc
Color
Blue
Bright green
Pale/Yellowish Green
Orange to red
Blue
Blue
non-halide
Green
halide
Blue-green
Gold
Blue
Lilac to red
Magenta to carmine
Bright white
Yellowish green
Yellowish green
Intense yellow
Pale bluish green
Blue
Red to purple-red
Pale green
Azure blue
Crimson
Pale green
Pure green
Bluish green to whitish green
Let’s Review Energy – Radiation of different wavelengths
affect matter differently – certain wavelengths (near
infrared) may burn your skin with a heat burn, overexposure
to X radiation causes tissue damage. These diverse effects
are due to differences in the energy of the radiation.
Radiation of high frequency and short wavelength are more
energetic than radiation of lower frequency and longer
wavelength.
While light exhibits many wavelike properties, it can also
be thought of as a stream of particles. Each particle of
light carries a quantum of energy. Einstein called these
particles PHOTONS. A photon is a particle of
electromagnetic radiation having zero mass and
carrying a quantum of energy.
Albert Einstein
• The electromagnetic spectrum is continuous showing
no breaks between different energy waves.
• When looking at visible, ‘white light’ through a
spectroscope there is a continuous spectrum of
coloured light – R O Y G B V (the colours of the
rainbow).
• Red has the lowest energy with the largest
wavelength, smallest frequency and violet has the
greatest , with lower wavelength and greater
frequency.
The Hydrogen-Atom Line-Emission
Spectrum
When investigators passed an electric current through
a vacuum tube containing hydrogen gas at low
pressure, they observed the emission of a characteristic
pinkish glow. When a narrow beam of the emitted light
was shined through a prism, it was separated into a
series of specific frequencies (and therefore specific
wavelengths, c =) of visible light. The bands of light
were part of what is known as hydrogen’s LINEEMISSION SPECTRUM.
When gaseous atoms of elements are heated and the
electrons absorb sufficient energy to ‘escape’ their
ground state configuration, ‘excited’ electrons jump to
higher energy levels ( the greater the distance between
the nucleus of the atom and the energy level the
greater the energy needed by the electron to travel to
that level).
‘Excited electrons’ are unstable and so return to
ground state releasing the absorbed energy in discrete
energy emissions patterns. In the visible spectrum,
these emissions appear as discrete lines of colour in a
spectroscope.
Bohr’s Theory of the Atom:
Bohr’s Model of the Atom
The hydrogen atom emits visible light when its electron moves from the third through sixth energy
levels to the second energy level. Ultraviolet radiation is emitted when the electron moves from the
second through sixth energy levels to the first energy level. Infrared radiation is emitted when the
electron moves from the fourth through sixth energy levels to the third energy level. Complete the
following diagram so the purple and red arrows were used to represent the transitions that result in
ultraviolet and infrared emissions to the diagrams below.
FLAME TESTS
Flame tests rely on the idea that each element has a
characteristic set of emissions and will produce a
unique and characteristic colour when heated.
The sample is identified by comparing the observed
flame color against known values from a table or chart.
Q: “ Spectra lines are the fingerprints of elements”.
Explain what is meant by this statement.
Q: According to the Bohr theory, what happens to an
electron in an atom as it absorbs energy and as it
releases energy?