quantum mechanical nature of the atom Flashcards
Outline the three Limitations of Rutherford’ Atomic Model
- failed to address how and why the electrons were stable in their orbits. In other words, electrons did not decay to collide with the nucleus.
- could not give a description of where the electrons were.
- the constituents of nucleus were unknown
Outline the three postulates in Bohr’s atomic mode
- Electrons exist and orbit in stable and circular orbits about the nucleus under the influence of electrostatic attraction. In these orbits, electrons do not emit energy.
- Energy is absorbed or emitted in specific packets called quanta when electrons move from one stable energy level to another. The photon emitted has energy given by E = Ef - Ei
- Electrons orbit the nucleus such that the angular momentum of electrons is quantised.
How does an electron reach a higher energy level?
Through the absorption of energy
What happens when an electron returns to its ground state (usual energy level)?
the energy that was absorbed is now emitted in the form of visible light
What is the balmer series?
The emission spectrum of hydrogen produced when an electron returns to the second electron orbit (n = 2)
Which colours are associated with 3–>2, 4–>2, 5–>2, 6–>2, 7+–>2 respectfully?
Red, aqua, blue, violet, ultraviolet
Outline the limitations of Bohr’s model
- model is a combination of both classical and quantum physics. The circular motion of electrons stems from classical physics while the quantisation of its momentum is an application of quantum physics.
- lack of evidence supporting his postulates and model, thus having no theoretical justification. There was also no explanation as to why no energy is emitted from the orbiting electrons
- Relative Intensity of the spectral lines could not be explained when observing the spectrum. Some lines appeared brighter than others
- The Zeeman Effect, occurring when a strong magnetic field was passed through the discharge tube (containing hydrogen) increasing the hyperfine splitting, also could not be explained by the model.
Outline how Bohr used LOCOE to create Rydberg’s equation
Bohr postulated that an electron in a discrete orbit (energy level) does not emit energy. Therefore, when an electron returns to a lower energy level, it must emit the exact amount of energy it first absorbed to reach that energy level. In other words, the energy emitted by an electron during spectroscopy equals to the amount absorbed.
Outline De Broglie’s Hypothesis of Matter Waves
De Broglie postulated that electrons, when orbiting the nucleus, act as standing waves (stationary waves). Standing waves are resulted from two waves travelling in opposite directions and out of phase by exactly one wavelength. This causes the two waves to superimpose and form a standing wave whose amplitude is zero. The energy of the two waves also cancel each other out. (lander = h/mv)
How does De Broglie’s hypothesis explain one of Bohr’s postulates – that electrons orbit the nucleus in stable energy states, without emitting energy?
By understanding electrons’ orbits as standing waves which do not release nor absorb energy because standing waves have a closed orbit with no movement of energy, and therefore the electron is contained within the orbit and is therefore stable.
Which de Broglie’s matter-wave equation is consistent with Bohr’s third postulate - the angular momentum of an electron in a stable energy orbit is quantised, and why?
mvr = nh/2pi (lander=h/mv, 2pir=nh/mv) because the number of electron wavelengths in an orbit increases with energy level.
What is the limitation to de Broglie’s matter wave theory?
It is difficult to understand how electrons’ physical motion allows them to adopt properties of a standing wave while being under the influence of electrostatic attraction exerted by the nucleus.
