The existence of a maximum oxidation number of +6 for both uranium (Z = 92) and tungsten (Z = 74) prompted the placement of U under W in early periodic tables. When the element after uranium, neptunium (Z = 93), was discovered in 1940, its properties did not correspond to those of rhenium (Z = 75), and this cast doubt on the original placement of uranium. Using standard potential data from Resource section 2, discuss the differences in oxidation state stability between Np and Re.

Data from Resource section 2.

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Atom 1 H 1s¹ 2 He 1s² 3 Li [He]2s¹ 4 Be [He]2s² 5 B [He]2s²2p¹ 6 C [He]2s²2p² 7 N [He]2s²2p³ 8 0 [He]2s²2p¹ 9 F [He]2s²2p³ 10 Ne [He]2s²2p 11 Na [Ne]3s¹ 12 Mg [Ne]3s² 13 Al [Ne]3s²3p¹ 14 Si [Ne]3s²3p² 15 P [Ne]3s¹3p¹ 16 S [Ne]3s²3p¹ 17 CI [Ne]3s 3ps [Ne]3s²3p6 16 18 Ar Ionization energy (ev) 4 4₂ Electron affinity E (ev) 4 13.60 24.59 54.51 5.320 75.63 122.4 9.321 18.21 153.85 8.297 25.15 37.93 +0.277 11.257 24.38 47.88 +1.263 14.53 29.60 47.44 -0.07 13.62 35.11 54.93 +1.461 17.42 34.97 62.70 +3.399 21.56 40.96 63.45 -1.2 5.138 47.28 71.63 +0.548 7.642 15.03 80.14 ≤0 5.984 18.83 28.44 +0.441 8.151 16.34 33.49 +1.385 10.485 19.72 30.18 +0.747 10.360 23.33 34.83 +2.077 +3.617 -1.0 12.966 23.80 39.65 15.76 27.62 40.71 +0.754 -0.5 +0.618 0 Atom 19 K [Ar]4s¹ 20 Ca [Ar]4s² [Ar]3d¹4s² 21 Sc 22 Ti [Ar]3d²4s² 23 V [Ar]3d³4s² 24 Cr [Ar]3d³4s¹ 25 Mn [Ar]3d³4s² 26 Fe [Ar]3d 4s² 27 Co [Ar]3d²4s² 28 Ni [Ar]3d³4s² 29 Cu [Ar]3d¹04s¹ 30 Zn [Ar]3d¹04s² 31 Ga [Ar]3d¹4s²4p¹ 32 Ge [Ar]3d¹04s²4p² 33 As [Ar]3d¹04s²4p³ 34 Se [Ar]3d¹04s²4pª 35 Br [Ar]3d¹04s²4p³ 36 Kr [Ar]3d¹04s²4p6 Ionization energy (eV) 13 31.62 45.71 11.87 50.89 12.80 24.76 1₁ 4.340 6.111 6.54 6.82 13.58 27.48 6.74 14.65 29.31 6.764 16.50 30.96 7.435 15.64 33.67 7.869 16.18 30.65 7.876 17.06 33.50 7.635 18.17 35.16 7.725 20.29 36.84 9.393 17.96 39.72 5.998 20.51 30.71 7.898 15.93 34.22 9.814 18.63 28.34 9.751 21.18 30.82 11.814 21.80 36.27 13.998 24.35 36.95 Electron affinity E (EV) +0.502 +0.02 +0.30 +1.2 +0.81 +2.021 +3.365 -1.0