Actinides (Actinide Series)
Actinium to lawrencium, elements 89 to 103: the 5f-block, all radioactive, including uranium and plutonium.
89AcActinium90ThThorium91PaProtactinium92UUranium93NpNeptunium94PuPlutonium95AmAmericium96CmCurium97BkBerkelium98CfCalifornium99EsEinsteinium100FmFermium101MdMendelevium102NoNobelium103LrLawrencium
What they have in common
All actinides are radioactive. Only thorium and uranium occur in large amounts naturally; the elements after uranium (the transuranium elements) were first made in reactors and accelerators from 1940 onwards, many by Glenn Seaborg’s team at Berkeley.
Unlike the lanthanides, the early actinides show many oxidation states (uranium from +3 to +6) because 5f electrons are less deeply buried than 4f. Uranium-235 and plutonium-239 are fissile and power nuclear reactors.
- All radioactive
- Wide range of oxidation states in the early members
- Dense, reactive metals
Actinides at a glance
| Element | Z | Mass | Configuration | Valence e⁻ | Charges | EN | Radius (pm) |
|---|---|---|---|---|---|---|---|
| Actinium (Ac) | 89 | [227] | [Rn] 6d1 7s2 | 3 | 3+ | 1.1 | — |
| Thorium (Th) | 90 | 232.038 | [Rn] 6d2 7s2 | 4 | 4+ | 1.3 | — |
| Protactinium (Pa) | 91 | 231.036 | [Rn] 5f2 6d1 7s2 | 3 | 5+ | 1.5 | — |
| Uranium (U) | 92 | 238.029 | [Rn] 5f3 6d1 7s2 | 3 | 6+, 4+ | 1.38 | — |
| Neptunium (Np) | 93 | [237] | [Rn] 5f4 6d1 7s2 | 3 | 5+ | 1.36 | — |
| Plutonium (Pu) | 94 | [244] | [Rn] 5f6 7s2 | 2 | 4+ | 1.28 | — |
| Americium (Am) | 95 | [243] | [Rn] 5f7 7s2 | 2 | 3+ | 1.3 | — |
| Curium (Cm) | 96 | [247] | [Rn] 5f7 6d1 7s2 | 3 | 3+ | 1.3 | — |
| Berkelium (Bk) | 97 | [247] | [Rn] 5f9 7s2 | 2 | 3+ | 1.3 | — |
| Californium (Cf) | 98 | [251] | [Rn] 5f10 7s2 | 2 | 3+ | 1.3 | — |
| Einsteinium (Es) | 99 | [252] | [Rn] 5f11 7s2 | 2 | 3+ | 1.3 | — |
| Fermium (Fm) | 100 | [257] | [Rn] 5f12 7s2 | 2 | 3+ | 1.3 | — |
| Mendelevium (Md) | 101 | [258] | [Rn] 5f13 7s2 | 2 | 3+ | 1.3 | — |
| Nobelium (No) | 102 | [259] | [Rn] 5f14 7s2 | 2 | 3+ | 1.3 | — |
| Lawrencium (Lr) | 103 | [262] | [Rn] 5f14 7s2 7p1 | 2 | 3+ | 1.3 | — |
Questions students ask
Which actinides occur naturally?
Thorium and uranium in quantity; actinium, protactinium and traces of neptunium and plutonium form in uranium ores.