12.1 - The mass spectrometer

Stages of operation:

1. injection
2. vaporisation
3. ionisation
4. acceleration
5. deflection
6. detection
   

Substance to be tested is vaporised (by heat, vacuum) then ionised by electric current. Ions are accelerated through an electric field, then deflected by a magnetic field. Ions are then detected...the angle of deflection reflects their mass to charge ratio.

The angle of deflection of each fragment is proportional to it's mass, and so it is possible to find the relative atomic mass of each 'spike' the height of the spike represents the frequency, therefore, the abundance can be calculated. The relative atomic mass is the average of the isotope masses times their frequencies.

12.2 - Electronic structure of atoms

12.2.1 "State and explain how evidence from first and successive ionization energies accounts for the existence of the main energy levels and sub-levels.
Interpretation of graphs of first ionization and successive ionization energies versus atomic number provides evidence for the existence of the main energy levels and sub-levels"

Successive electrons can be stripped from an atom until there is only the nucleus left. If the energy required to achieve this for each electron is plotted on a graph (with a log scale) against ionisation number, the 'jumps' in the required energy clearly show the main and sub energy levels.

12.2.2 State how orbitals are labelled. Limit this to n < 5.

n = (1, s) (2, sp) (3, spd) (4 spdf)

12.2.3 State the relative energies of s, p, d and f orbitals.

Energies of sub-shells : s < p < d < f (in a given energy level)

12.2.4 State the number of orbitals at each energy level.

Number of orbitals at each level : s=1, p=3, d=5, f=7

12.2.5 Draw the shape of an s orbital and the shapes of the px, py and pz orbitals.

Shapes of orbitals:

• s orbital is a sphere around the nucleus.
• p orbitals are shaped like a figure 8 (and there are 3 of them at 90 degrees around the nucleus.

12.2.7 - The Aufbau Principle

Move diagonally down and left through each diagonal...ie 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d...

Pauli's exclusion principle says that there can only be 2 electrons in each orbital (with opposite spins).

Hund's rule says that each orbital should be half filled before any is completely filled (since there is less repulsion if all electrons have the same spin). Electrons will therefore fill the lowest energy levels (ie 1 then 2 and so on) with two going in each orbital, but only doubling up when all orbitals in the level are filled.

Systematically fill the orbitals as shown above up to Z = 56.

This can be abbreviated by writing [x] where x is a noble gas.

The periodic table

The small double column on the left (groups 1 and 2) is the s shell being filled.

The block on the right is the p shell being filled (groups 3 to 8)

The d block (in the middle) is the d shell being filled.

Resources

atomic theory

periodic table for interactive configurations.

mass spectra of common elements

Useful links