Zadanie 2b

(i) Sr has more protons/a higher nuclear charge than Rb ✔

Rb and Sr have the same shielding/the same number of occupied energy levels ✔ «accept for M2: Sr has the smaller atomic radius, so the electron removed is closer to the nucleus»

(ii) the valence electron/bonding electrons in Rb are more shielded «by inner electrons», i.e. Rb has more occupied energy levels than K ✔ «accept: Rb has the larger atomic radius, if that point was not already used as the explanation in (i)»

(iii) nitrogen has three unpaired electrons in the 2p sub-level «2p_x¹2p_y¹2p_z¹» AND oxygen has one 2p orbital containing a pair of electrons «two unpaired, 2p_x²2p_y¹2p_z¹» ✔

repulsion between the paired electrons in oxygen «makes one of them easier to remove, so less energy is needed» ✔

(i) [2] M1: higher nuclear charge/more protons in Sr (required); M2: same shielding/same number of occupied energy levels, OR accept Sr having a smaller atomic radius so that the electron removed is closer to the nucleus. (ii) [1] one marking point: more shielding/more occupied energy levels in Rb than in K; a larger atomic radius for Rb is allowed if it was not used as the explanation in (i). (iii) [2] M1: electron arrangement in the 2p sub-level of both elements (N with three unpaired electrons, O with one pair); orbital diagrams are accepted; M2: repulsion between the paired electrons in oxygen. Do not award M2 for a statement about nuclear charge or atomic radius alone.