The second main energy level contains s and p sub-levels. The s sub-level is full after two electrons have been added successively (Li & Be). The p sub-level is then successively filled until six electrons have been added to give Ne. After Ne the third level starts to be filled (3s) showing that the maximum number of electrons that can occupy the 2p sub-level is 6.

It is easier to remove a p electron from Al ([Ne]3s²3p¹) than it is to remove an s electron from Mg ([Ne]3s²).

K has a very low IE with the configuration [Ar]4s¹ so the 4s fills before the 3d sub-level.

The regular increase from B to N then the drop between N and O shows that the three p orbitals are filled singly before the electrons are paired up.

The values will all be higher but the repeating pattern has shifted one place to the right, i.e. the plot would need to be shifted to the left by 1 atomic number to retain the same pattern against atomic number (but at a higher energy values) as the peaks in each period will now be given by Li⁺, Na⁺ and K⁺ etc.

For the 4^th ionization energy the equation is V³⁺⁽g) → V⁴⁺(g) + e^– and for the 5^th ionization energy the equation is V⁴⁺(g) → V⁵⁺(g) + e−. The V⁴⁺ ion will attract electrons more strongly than the V³⁺ ion so the 5^th electron will be harder to remove.

Both the 4th and the 5th ionisation energies involve the loss of 3d electrons. The 5^th ionisation ionization gives the V⁵⁺ ion with an electronic configuration of 1s²2s²2p⁶3s²3p⁶ i.e. the same as the noble gas argon. It will be much more difficult to remove the 6^th electron as it involves removal of a 3p electron and the 3p level is much more strongly attracted to the nucleus than a 3d electron.

E = hv = hc/λ
=(6.63 x 10^-34 x 3.00 x 10⁸)/9.12 x 10⁻⁸ = 2.18 x 10⁻¹⁸ J for one electron

= 2.18 x 10⁻¹⁸ x 6.02 x 10²³ = 1.31 x 10⁶ J mol⁻¹ = 1310 kJ mol⁻¹ (to 3 SF)

The convergence line in the ultraviolet spectrum is due to the transition from n = ∞ to the lowest level n = 1 which is the level occupied by the one hydrogen electron in the ground state. The convergence line in the visible spectrum is due to the transition from n = ∞ to n = 2.