4 - ionisation energy

• the electrons in atoms are attracted to the positive nucleus
• removing electrons from atoms is called ionisation
• ionisation energy is the energy required to remove one electron from an atom in a gaseous state
• in general, ionisation energy increases across a period as the nuclear charge increases moving along the period as more protons are added and so the outer electrons experience a greater attraction as the atom increases in atomic number
• small decreases of ionisation energy are seen in the second and third period
• decreases

  beryllium (Be) - boron (B)

  nitrogen (N) - oxygen (O)

  Phosphorus (P) - sulfur (S)
• the decreases in ionisation energy is because the added electron is in the new p subshell which has a slightly higher energy level and is slightly further from the nucleus
• the S2 electrons provide sheilding for the gorup 3 elements
• the explanation for the decrease from group 5 to group 6 in period 2 (N-O) and period 3 (P-S) is due to the stablity of the p orbitals
• during ionisation the electrons for the group 6 elements are to be removed from the p4 configuration. The fourth electron in the 3p orbital leads to the electron-electron repulsion
• the attraction between the fourth electron and the nucleus means the electron is easier to remove
• the p subshell is the most stable then it contains either 3 or 6 electrons
• the d subshell is at its most stable when it contains either 5 or 10 electrons
• the more stable the electron configuration is, the harder it is to remove the outer electron from its nucleus, subsequently the higher the ionisation
• the periodic table can be divided into 4 blocks, depending on which subshell the electrons are located in