MARY - Topic 3 Flashcards
What did Bohr propose?
A new model for the atom. He proposed that electrons travel in circular orbits around the nucleus, and the electrons held in these orbits by electrostatic forces with the nucleus.
What does the Rydberg equation give?
It gives the difference in orbit frequencies?
What is zero energy taken as?
The point where the electron is removed.
What happens at ionisation?
n = infinity
What does n = 1 correspond to?
The lowest energy state, which is the orbit closest to the nucleus.
What are the different n numbers?
Quantum numbers
What is the difference between the Rutherford and Bohr model?
The Rutherford model of the atom predicted unstable atoms, where electrons lose energy as they travel. In the Bohr model, the orbits have specific energies and electrons can only gain or lose energy by changing orbit.
What were the +ves of Bohr’s model?
- Electrons in fixed orbits
1 = worked well for hydrogen 2 = explained the Rydberg formula for the emission lines of the hydrogen spectrum 3 = quantum no's and quantisation introduced
What were the -ves of Bohr’s model?
1 = Useless for anything apart from Hydrogen 2 = didn't explain why only certain orbits were allowed
What does Rh =?
3.29 x 10^-15
What is the radius of hydrogen?
0.529Å
It’s the distance from an electron in orbit n = 1, from the nucleus in a ground-state H atom.
What did de Broglie propose?
1924
All matter had wave like properties.
What is de Broglie’s formula?
Wavelength = h/mv
How did de Broglie change Bohr’s model?
Electrons moving in a wave like motion about a nucleus, and each electron orbit was considered to be a fixed number x the wavelength.
What do the integer values of quantum no.s =?
The no. of wavelengths in a given orbit.
What was the Davisson-Germer experiment?
1925
Shined an electron beam at a nickel crystal and recorded the pattern. The pattern had areas of light and dark, due to constructive/destructive interference of the electron beam.
Constructive/destructive interference is only relevant for waves, and the pattern was a diffraction pattern. They were able to observe the pattern because the wavelength of the electron beam was close to the spacing between the nickel atoms.
What were the conclusions of electrons?
They have both particle and wavelike properties, so it replaces the certainty with probability.
What is the Heisenberg Uncertainty Principle?
When objects have wave-like propertie, we can’t measure their momentum and position at the same time.
To determine the position of an electron, the momentum would be affected.
To determine the momentum, the position would be affected.
What did Heisenberg determine about uncertainty?
The lower limit to this uncertainty is h/4pi.
What is the uncertainty value?
5.27 x 10^-35 Js
Why can’t we ignore uncertainty?
For large objects it’s a low value however it’s huge for electrons, so we can’t ignore it for objects with small masses.