1.3.2Additional lessons
Emission Spectra — IB Chemistry HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 9 of 172
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4Continuous and Line Spectra
The light from a hot source can show two different types of spectrum.
Continuous
- Continuous White light split by a prism shows a continuous band of colours with every wavelength present.
Line emission
- Line emission Excited atoms of an element emit light only at specific wavelengths, giving bright lines on a dark background.
Fingerprint
- Fingerprint Each element has its own pattern of lines, which allows it to be identified.
Meaning
- Meaning Only certain energies are possible in the atom, so energy levels are quantised.
Part 2 of 4Origin of the Lines
The hydrogen atom spectrum can be explained in terms of electron transitions.
1
Energy supplied by an electric discharge promotes an electron from a low level to a higher energy level.
2
The excited state is unstable, so the electron falls back to a lower level.
3
The energy difference between the two levels is released as one photon, with ΔE = hν.
4
Because the levels have fixed energies, only photons of certain frequencies are emitted, giving distinct lines.
5
The lines get closer together towards higher frequency, since energy levels converge as n increases.
Part 3 of 4Hydrogen Series
Hydrogen Series
Lyman series
- Lyman series Transitions ending at n = 1 give lines in the ultraviolet region, as these have the largest energy gaps.
Balmer series
- Balmer series Transitions ending at n = 2 give lines in the visible region.
Paschen series
- Paschen series Transitions ending at n = 3 give lines in the infrared region.
Convergence
- Convergence In each series the lines converge at high frequency, where the electron leaves the atom.
| Series | Ends at | Region |
|---|---|---|
| Lyman | n = 1 | Ultraviolet |
| Balmer | n = 2 | Visible |
| Paschen | n = 3 | Infrared |
Part 4 of 4Exam Checklist & Tips
1.3.2 – Key Points for the Exam
- Emission spectrum The set of frequencies of radiation emitted by excited atoms.
- Energy level A fixed energy that an electron in an atom can have.
- Excited state A state with an electron in a higher energy level than normal.
- Convergence The lines in a series getting closer together at high frequency.
Common Mistakes
- Saying that the electron emits light when it moves up to a higher level.
- Thinking that line spectra show every colour of the rainbow.
- Stating that bigger electron jumps give longer wavelengths.
- Describing the lines as having equal spacing.
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