MARY - Topic 3

Question 1

What did Bohr propose?

Answer 1

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.

Question 2

What does the Rydberg equation give?

Answer 2

It gives the difference in orbit frequencies?

Question 3

What is zero energy taken as?

Answer 3

The point where the electron is removed.

Question 4

What happens at ionisation?

Answer 4

n = infinity

Question 5

What does n = 1 correspond to?

Answer 5

The lowest energy state, which is the orbit closest to the nucleus.

Question 6

What are the different n numbers?

Answer 6

Quantum numbers

Question 7

What is the difference between the Rutherford and Bohr model?

Answer 7

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.

Question 8

What were the +ves of Bohr’s model?

Answer 8

• 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

Question 9

What were the -ves of Bohr’s model?

Answer 9

1 = Useless for anything apart from Hydrogen
2 = didn't explain why only certain orbits were allowed

Question 10

What does Rh =?

Answer 10

3.29 x 10^-15

Question 11

What is the radius of hydrogen?

Answer 11

0.529Å

It’s the distance from an electron in orbit n = 1, from the nucleus in a ground-state H atom.

Question 12

What did de Broglie propose?

Answer 12

1924

All matter had wave like properties.

Question 13

What is de Broglie’s formula?

Answer 13

Wavelength = h/mv

Question 14

How did de Broglie change Bohr’s model?

Answer 14

Electrons moving in a wave like motion about a nucleus, and each electron orbit was considered to be a fixed number x the wavelength.

Question 15

What do the integer values of quantum no.s =?

Answer 15

The no. of wavelengths in a given orbit.

Question 16

What was the Davisson-Germer experiment?

Answer 16

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.

Question 17

What were the conclusions of electrons?

Answer 17

They have both particle and wavelike properties, so it replaces the certainty with probability.

Question 18

What is the Heisenberg Uncertainty Principle?

Answer 18

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.

Question 19

What did Heisenberg determine about uncertainty?

Answer 19

The lower limit to this uncertainty is h/4pi.

Question 20

What is the uncertainty value?

Answer 20

5.27 x 10^-35 Js

Question 21

Why can’t we ignore uncertainty?

Answer 21

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.