Question

1) why do atoms have discrete spectral lines?

2) Is it possible for different atomic transitions, in a particular atom, to give off the same colour photons?why?

3) A beam of red photons and blue photons are sent through a diffraction grating simultaneously. Sketch the diffraction pattern of both colours.

4) The spectrometer provided is able to measure angles to a precision of 1 minute (1'). Given that 60'=1degree, convert the following angles, 31degree 21' and 12degree 5', into degrees.

Answer 1

1) These discrete lines are caused by discrete energy levels, as dictated by the Bohr model of the atom. When electrons jump up to an energy level because of excitation, and come down back down, they emit a photon or photons equal to the amount of energy needed to excite the electron in the first place. When electrons jump down to the second level, characterized by the Balmer series, they emit photons that are visible light.

For example, the diagram below explains the Hydrogen emmission spectra for visible light:
n = 4 --^-----e------------e------------------...
n = 3 --!------!-------------v---e------------...
...........!......! (blue)........! (red)
n = 2 --!------v-----------------v------------...
...........!
...........!
n = 1 -e--------------------------------------...

In this diagram, this explains two ways an electron on a hydrogen atom can emit visible spectra lines. By exciting the electron to the fourth energy level, it can go down to energy level 2 to produce a blue photon, or it can go down to energy level 3 and then energy level 2, which produces two photons, one of which is red.

There is no possible way for an electron to exist in between energy levels, and therefore emit other photons other than those described by spectral lines.

2) Yes , it is possible. Colours have a certain range of wavelength .So ,if energy from 2 different transitions fall in the same colour range , it is possible.

Electrons can only exist in certain areas around the nucleus called shells. Each shell corresponds to a specific energy level which is designated by a quantum number n. Since electrons cannot exist between energy levels, the quantum number n is always an integer value (n=1,2,3,4