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actinide





Actinides
element Z outermost
electrons
valences
actinium (Ac) 89 6d17s2 3
thorium (Th) 90 6d27s2 4
protactinium (Pa) 91 5f26d17s2 4, 5
uranium (U) 92 5f36d17s2 3, 4, 5, 6
neptunium (Np) 93 5f46d17s2 3, 4, 5, 6, 7
plutonium (Pu) 94 5f67s2 3, 4, 5, 6, 7
americium (Am) 95 5f77s2 3, 4, 5, 6
curium (Cm) 96 5f76d17s2 3, 4
berkelium (Bk) 97 5f97s2 3, 4
californium (Cf) 98 5f107s2 2, 3
einsteinium (Es) 99 5f117s2 2, 3
fermium (Es) 100 5f127s2 2, 3
mendelevium (Md) 101 5f137s2 2, 3
nobelium (No) 102 5f147s2 2, 3
lawrencium (Lr) 103 5f146d17s2 3
Any member of the series of elements with atomic numbers from 89 (actinium) to 103 (lawrencium). The actinides are, in order of increasing atomic number: actinium, thorium, protactinium, uranium, neptunium, plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium, and lawrencium. Each actinide is analogous to the corresponding member of the lanthanide series. They are separated by ion-exchange chromatography.

The elements through uranium occur in nature; except actinium, they show valences higher than +3. The transuranic elements are synthetic; the +3 valence state becomes progressively more stable, and higher valences less stable.


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