CHEM1011 Lecture Notes - Lecture 7: Rydberg Constant, Rydberg Formula, Balmer Series
CHEM1011 – Chemistry 1A – Part 4
LEC 7: *Continued
• The speed of light:
o = wavelength (m)
o = frequency (s-1)
o = speed of light (m s-1)
• Experimentations on the photoelectric effect showed that electrons will only be
ejected at a certain frequency and no less. This provided evidence to show that
atomic orbitals have discrete energy levels and energy needs to exceed it in
order for electrons to be omitted. – threshold frequency.
• Light behaves as a particle: wave-particle duality.
• Planck equation:
E = energy (J)
h = Planck constant (6.626 x 10-34 J s)
v = frequency (s-1 = Hz)
• Eess eeg eitted the photo that is’t euied to eak the idig
energy will be converted to kinetic energy when the electron is emitted.
• E>0 : electron in motion
• E=0 : free electron at rest
• E<0 : electron bound to atom
o Electrons have a negative energy when bound as energy is required to
free the bound electron.
• Absorption of light: light is absorbed/used
o When white light is passed through a slit and a specific gas, there will be
black lines breaking up its absorption spectrum. These black lines
represent the wavelengths of light that the gas absorbs in order for its
electrons to leave their atomic orbitals.
▪ This is known as quantisation.
o Each element will have a different absorption spectrum as the
frequencies of light (energy levels) required are discrete and unique to
the individual element (making it a useful tool in forensic chemistry to
identify chemicals).
o = will be positive as energy is being absorbed.
• Emission of light: light is released
o When gases are heated by an electrical discharge it produces light at
specific frequencies, with the rest being black. This indicates the
wavelengths of light that are emitted by the gas molecules, which are
complimentary to the elements absorption spectrum (because energy
levels are discrete).
o This is called an emission spectrum.
o = will be negative as it releases energy.
• When an electron in an atom goes from one energy level to another, a photon is
emitted with energy equal to the difference between the two levels
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Document Summary
Lec 7: *continued: the speed of light: , = wavelength (m, = frequency (s-1, = speed of light (m s-1, planck equation: = E = energy (j) h = planck constant (6. 626 x 10-34 j s) v = frequency (s-1 = hz: experimentations on the photoelectric effect showed that electrons will only be ejected at a certain frequency and no less. This provided evidence to show that atomic orbitals have discrete energy levels and energy needs to exceed it in order for electrons to be omitted. Atoms eventually give up their excess energy and return to ground state (stable): h(cid:455)d(cid:396)oge(cid:374)"s ato(cid:373)i(cid:272) e(cid:374)e(cid:396)g(cid:455) levels: considered to be emitted from the atom. Calculations: lyman series (uv) and balmer series (visible light, combination of speed of light and planck equations, as energy levels approach n = the differences become so small that they are.