Neptunium commonly forms Np3+ Np4+ Np5+ Np6+ in introductory ionic compounds.
| Element | Neptunium |
|---|---|
| Symbol | Np |
| Atomic number | 93 |
| Common ionic charge | +3, +4, +5, +6 |
| Common ions | Np3+, Np4+, Np5+, Np6+ |
Images are used as visual references; charge rules still depend on the compound.
Neptunium is [Rn]5f4 6d1 7s2, sitting between uranium (+6-loving) and plutonium (+4-loving); its compromise favorite is +5. Like uranium it caps its high states in 'yl' oxo-cations — NpO2+ mirrors uranyl but with one less positive charge and stubbornly weak complexing habits.
This is a classroom reference range, not an exhaustive list of all oxidation states.
Treating neptunium as a lab-only footnote. Np-237 (half-life 2.1 million years) is a principal long-term heat and dose driver of spent nuclear fuel, and the mobility of NpO2+ — which sticks poorly to minerals — is a headline problem for waste repositories. The +5 charge is a policy issue.
Two O at -4 with overall charge +1 gives Np = +5. Compare uranyl UO2 2+ (U = +6): same architecture, one electron more retained — the fingerprint of moving one box right in the actinide row.
Neptunium chloride
Np3+ balances chloride ions.
Neptunium oxide
Neptunium can form oxides where total positive and negative charge balances.
Uranium was named for Uranus; the next element (1940, Berkeley) took Neptune, the next planet out — and plutonium then followed with Pluto. The bottom row of the table doubles as a solar-system tour.
Roughly: Np3+ purple-blue, Np4+ yellow-green, NpO2+ green, NpO2 2+ pink — four charges you can literally tell apart by eye, a favorite demonstration of actinide redox richness (in licensed labs).
Np-237 targets are irradiated to breed Pu-238, the heat source powering deep-space probes — neptunium as feedstock for the batteries of Voyager's successors.
Combine positive and negative ions so the total charge is zero — or let the ionic compound calculator do the crossing for you. The full chart lives on the periodic table with charges.
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