Actinide - Properties

Properties

Actinides have similar properties to lanthanides. The 6d and 7s electronic shells are filled in actinium and thorium, and the 5f shell is being filled with further increase in atomic number; the 4f shell is filled in the lanthanides. The first experimental evidence for the filling of the 5f shell in actinides was obtained by McMillan and Abelson in 1940. As in lanthanides (see lanthanide contraction), the ionic radius of actinides monotonically decreases with atomic number (see also Aufbau principle).

Properties of actinides (the mass of the most long-lived isotope is in square brackets)
Property Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
Core charge 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103
atomic mass 232.0381 231.03588 238.02891
Number of natural isotopes 3 9 5 9 4 5 5 8 2 5
Natural isotopes 225, 227–228 226–232, 234–235 231, 233–236 232–240 237–240 238–240, 242, 244 241–245 242–249 249–250 249–253
Longest-lived isotope 227 232 231 238 237 244 243 247 247 251 252 257 258 259 262
Half-life of the longest-lived isotope 21.8 years 14 billion years 32,500 years 4.47 billion years 2.14 million years 80.8 million years 7,370 years 15.6 million years 1,400 years 900 years 1.29 years 100.5 days 52 days 58 min 261 min
Electronic configuration in the ground state 6d17s2 6d27s2 5f26d17s2or 5f16d27s2 5f36d17s2 5f46d17s2or 5f57s2 5f67s2 5f77s2 5f76d17s2 5f97s2or 5f86d17s2 5f107s2 5f117s2 5f127s2 5f137s2 5f147s2 5f147s27p1
Oxidation state 3 3, 4 3, 4, 5 3, 4, 5, 6 3, 4, 5, 6, 7 3, 4, 5, 6, 7 2, 3, 4 3, 4 3, 4 2, 3 2, 3 2, 3 2, 3 2, 3 3
Metallic radius, nm 0.203 0.180 0.162 0.153 0.150 0.162 0.173 0.174 0.170 0.186 0.186
Ionic radius, nm:
An4+
An3+


0.126

0.114

0.104
0.118

0.103
0.118

0.101
0.116

0.100
0.115

0.099
0.114

0.099
0.112

0.097
0.110

0.096
0.109

0.085
0.098

0.084
0.091

0.084
0.090

0.084
0.095

0.083
0.088
Temperature, °C:
melting
boiling

1050
3300

1750
4800

1572
4400

1130
3800

640
3900

640
3230

1176
2610

1340

1050

900

860

1530

830

830

1630
Density, g/cm3 10.07 11.78 15.37 19.06 20.25 19.84 11.7 13.51 14.78 15.1 8.84
Standard electrode potential, V:
E° (An4+/An0)
E° (An3+/An0)


−2.13

−1.83

−1.47

−1.38
−1.66

−1.30
−1.79

−1.25
−2.00

−0.90
−2.07

−0.75
−2.06

−0.55
−1.96

−0.59
−1.97

−0.36
−1.98

−0.29
−1.96


−1.74


−1.20

-
−2.10
Color
4+
3+


Colorless

Colorless
Blue

Yellow
Dark blue

Green
Purple

Yellow-green
Purple

Brown
Violet

Red
Rose

Yellow
Colorless

Beige
Yellow-green

Green
Green


Pink








Approximate colors of actinide ions in aqueous solution
Oxidation state 89 90 91 92 93 94 95 96 97 98 99
+3 Ac3+ Th3+ Pa3+ U3+ Np3+ Pu3+ Am3+ Cm3+ Bk3+ Cf3+ Es3+
+4 Th4+ Pa4+ U4+ Np4+ Pu4+ Am4+ Cm4+ Bk4+ Cf4+
+5 PaO+
2
UO+
2
NpO+
2
PuO+
2
AmO+
2
+6 UO2+
2
NpO2+
2
PuO2+
2
AmO2+
2
+7 NpO3+
2
PuO3+
2
5-

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