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Light and Atomic Spectra: Flashcards

Revise wavelength, frequency and photon energy, line spectra and the Bohr model of hydrogen.

10 cardsIntermediate

10 cards

  1. Question
    Give the equation linking the speed of light, wavelength and frequency.
    Answer

    c=λνc = \lambda\nu, with c=2.998×108c = 2.998 \times 10^{8} m/s

  2. Question
    Give the equation for the energy of a photon.
    Answer

    E=hν=hcλE = h\nu = \dfrac{hc}{\lambda}, with h=6.626×10−34h = 6.626 \times 10^{-34} J s

  3. Question
    Which has more energy per photon: red light or violet light?
    Answer

    Violet: shorter wavelength, higher frequency, more energy.

  4. Question
    What is the approximate wavelength range of visible light?
    Answer

    About 400 nm (violet) to 700 nm (red).

  5. Question
    What is a line spectrum, and what does it show?
    Answer

    Light of only certain exact wavelengths, emitted by an excited element. It shows that electron energy levels are quantized.

  6. Question
    Give the Bohr energy of level n in hydrogen.
    Answer

    En=−2.179×10−18 Jn2E_n = -\dfrac{2.179 \times 10^{-18}\ \text{J}}{n^2}

  7. Question
    Why are the Bohr energies negative?
    Answer

    The electron is bound to the nucleus; zero energy means it has been removed (n = ∞).

  8. Question
    Which drops give hydrogen's visible lines?
    Answer

    Drops from higher levels down to n = 2 (656, 486, 434 and 410 nm).

  9. Question
    What is the frequency of 656 nm light?
    Answer

    (2.998 × 10⁸ m/s) ÷ (656 × 10⁻⁹ m) = 4.57 × 10¹⁴ s⁻¹

  10. Question
    How do you convert the energy of one photon into kJ/mol?
    Answer

    Multiply by Avogadro's number (6.022 × 10²³ mol⁻¹) and divide by 1000.