Developing Electronic Configuration
- Electrons move rapidly around the nucleus in energy shells
- If their energy is increased, then they can jump to a higher energy level
- The process is reversible, so electrons can return to their original energy levels
- When this happens, they emit energy
- The frequency of energy is exactly the same, it is just being emitted rather than absorbed:
The difference between absorption and emission depends on whether electrons are jumping from lower to higher energy levels or the other way around
- The energy they emit is a mixture of different frequencies
- This is thought to correspond to the many possibilities of electron jumps between energy shells
- If the emitted energy is in the visible region, it can be analysed by passing it through a diffraction grating
- The result is a line emission spectrum
Line emission spectra
The line emission (visible) spectrum of hydrogen
- Each line is a specific energy value
- This suggests that electrons can only possess a limited choice of allowed energies
- These packets of energy are called 'quanta' (plural quantum)
- What you should notice about this spectrum is that the lines get closer together towards the blue end of the spectrum
- This is called convergence and the set of lines is converging towards the higher energy end, so the electron is reaching a maximum amount of energy
- This maximum corresponds to the ionisation energy of the electron
- These lines were first observed by the Swiss school teacher Johannes Balmer, and they are named after him
- We now know that these lines correspond to the electron jumping from higher levels down to the second or n = 2 energy level
Successive ionisation energies
- The first electron removed has a low IE1 as it is easily removed from the atom due to the spin-pair repulsion of the electrons in the 4s orbital
- The second electron is more difficult to remove than the first electron as there is no spin-pair repulsion
- The third electron is much more difficult to remove than the second one corresponding to the fact that the third electron is in a principal quantum shell which is closer to the nucleus (3p)
- Removal of the fourth electron is more difficult as the orbital is no longer full, and there is less spin-pair repulsion
- The graph shows there is a large increase in successive ionisation energy as the electrons are being removed from an increasingly positive ion
- The big jumps on the graph show the change of shell and the small jumps are the change of subshell
Successive ionisation energies for the element calcium