Our simple model of the atom has its uses but in order to appreciate more subtle relationships between atoms, the periodic table and chemical reactions we need to have a more advanced approach. We don t need to know the ideas behind this advanced model merely the idea itself. Put simply it is as follows Firstly electrons are not simple particles but also have properties that suggest they are waves, secondly electrons are so small that it is not possible to tell where, precisely, they are in an atom. For our purposes the second of these ideas is the most relevant. We cannot know where they are but we can know roughly where they are.
How do we detect the position of an electron? To see something, light waves have to strike it and then be reflected back into our eyes.
Atoms can lose electrons when involved in bonding, this process is called ionisation and requires energy. The first ionisation energy is The amount of energy required per mole to remove an electron from each atom in the gas phase to form a singly positive ion (cation). M (g) M + (g) + e The ionisation energy is affected by the distance of the electron from the nucleus the repulsion by other electrons in the atom (shielding) Therefore the ionisation energy provides information about atomic structure.
You will recall from Grades 9 & 10 that the group number of an element is linked to the number of electrons in the valence shell and the period number is linked to the number of shells in the atom. e.g. Sodium is in group 1and period. An atom of sodium has 1 electron in its valence shell and has a total of shells. Because ionisation energies give us information about the structure of the atom
Atoms usually lose or gain a predictable number of electrons. However it is possible to remove all of the electrons from an atom if enough energy is supplied. The removal of electrons, one at a time, provides information about the structure of the atom.
+1 Successive ionisation energies of sodium + Log kj mol1 Why is the 1 st ionisation energy relatively low? The 1 st ionisation energy is low because the electron is far from the nucleus and well shielded by the inner shells of electrons. This is why sodium tends to lose this electron when bonding.
+ Successive ionisation energies of sodium + Log kj mol1 Why is there a big jump to the nd ionisation energy? There is a big jump to the nd ionisation energy due to electron is being removed from a shell that it closer to the nucleus therefore Greater pull by the nucleus Less shielding by inner electrons
+ Successive ionisation energies of sodium + Log kj mol1 Account for the pattern between the nd and 9 th ionisation energy. Between the nd and 9 th ionisation energies there is a steady increase due to removing electrons from an increasingly positive cation. However the increase is steady with no big jumps as they are being removed from the same shell.
Successive ionisation energies of sodium + + Log kj mol1
Successive ionisation energies of sodium + + Log kj mol1
Successive ionisation energies of sodium + + Log kj mol1
Successive ionisation energies of sodium +7 + Log kj mol1
Successive ionisation energies of sodium +8 + Log kj mol1
Successive ionisation energies of sodium +9 + Log kj mol1
Successive ionisation energies of sodium +10 + Log kj mol1 Why is there a big jump between the 9 th and 10 th ionisation energy? The 10 th electron is being removed from the inner shell. There is almost no shielding and it is very close to the nucleus.
Successive ionisation energies of sodium +11 + Log kj mol1 The 11 th ionisation energy shows only a slight increase from the 10 th as they are both being removed from the same shell.
The successive ionisation energies of an atom provide us with information about the number of shells present. Successive ionisation energies of sodium Shell Shell 1 Shell