Amber Wareham
Investigation 1.4.1
Title: Atomic Spectra
Purpose: The purpose of this investigation is to determine if one can distinguish an
unknown element based on observing the spectrum it produces.
Materials:
- eye protection
- spectroscope
- incandescent light source
- power supply
- fluorescent light source
- hydrogen gas discharge tube
- gas discharge tubes of air, helium, nitrogen, neon, and water vapour
Procedure: See Nelson “Chemistry 11” pg. 40-41
Observations:
Light/Element/Compound
Light Emitted
Flourescent
White
Incandescent
White
Helium
Salmon (pale pink)
Neon
Red-orange
Nitrogen
Salmon (pale pink)
Hydrogen
Pink faded to salmon to pink
Air
Pink
Water Vapour
Pink faded to salmon to pink
Line Spectrum
Amber Wareham
Analysis of Results:
i) page 41, questions (a,b,c):
a)) In this variation of the investigation, it was known what was in each
gas discharge tube prior to observing its line spectrum. However, of the
elements whose line spectra are documented in the appendix and if which
we observed, the line spectra recorded during the investigation are
accurate when compared with the appendix.
b)) While the incandescent light source exhibited a line spectrum of red
through violet, the spectrum of the fluorescent light source only showed
lines of red, green, indigo, and violet as distinguished colours. This
suggests that the light produced by the respective types of light involves
different chemical reactions with different elements and compounds.
c)) In this investigation, the elements that produced the largest number of
spectral lines were nitrogen and neon. In regards to electron transitions,
this suggests that the electrons of these elements are dropping to lower
energy levels in more combinations than other elements. This could be
caused by possibly because these elements are more reactive to heat or
because there is a stronger attraction between the electrons and the
protons in the nucleus.
ii) a)) Water vapour is made up of H2O, or hydrogen and oxygen, in its
gaseous state.
b)) Air consists essentially of oxygen, carbon, and nitrogen.
iii) page 42, questions (1-4)
1. When a gas is heated, it emits light because the extra energy causes the
electrons to become excited and able to make a transition to a higher
energy level. The light that is emitted is then produced when the
electrons release energy to make the transition to lower energy levels.
The energy released corresponds to wavelengths, accounting for different
colours.
2. The different colours in a line spectrum represent the wavelengths
corresponding to the released energy of electrons.
3. Different substances show different spectra because they have
different combinations of electrons. This causes the electrons to react
differently from substance to substance, depending on an element’s
reaction to heat or electricity, release energy in different combinations.
4. Based on the observation that sodium vapour lamps emit a yellow
light, it can be concluded that the electrons in sodium atoms are prone to
dropping to energy levels in a somewhat uniform and single combination,
where the electrons drop from a specific energy level to another specific
energy level emitting a yellow wavelength.
Conclusion: In conclusion, it is possible to distinguish an unknown gas in a gas discharge
tube by comparing the observed line spectrum with those of known elements.