Neptunium(IV) oxide

Neptunium(IV) oxide
Names
	IUPAC name Neptunium(IV) oxide
	Other names Neptunium oxide, neptunium dioxide
Identifiers
CAS Number	12035-79-9 ;
3D model (JSmol)	Interactive image;
ChemSpider	34997056;
ECHA InfoCard	100.031.651
EC Number	234-830-1;
PubChem CID	44148103;
	InChI InChI=1S/Np.2O/q+4;2*-2 Key: QKUTVYUEUPNRBO-UHFFFAOYSA-N;
	SMILES [O-2].[O-2].[Np+4];
Properties
Chemical formula	NpO2
Molar mass	269 g/mol
Appearance	Green cubic crystals
Density	11.1 g/cm3
Melting point	2,800 °C; 5,070 °F; 3,070 K
Structure
Crystal structure	Flourite (cubic), cF12
Space group	Fm3m, #225
Lattice constant	a = 543.4 pm
Formula units (Z)	4
Thermochemistry
Std molar; entropy (S⦵298)	19.19 ± 0.1 cal·mol−1·K−1 ; (80.3 ± 0.4 J·mol−1·K−1)
Std enthalpy of; formation (ΔfH⦵298)	−256.7 ± 0.6 kcal·mol−1 ; (−1074 ± 3 kJ·mol−1)
Related compounds
Other anions	Neptunium(III) chloride; Neptunium(IV) chloride
Other cations	Protactinium(IV) oxide; Uranium(IV) oxide ; Plutonium(IV) oxide; Americium(IV) oxide
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Neptunium(IV) oxide, or neptunium dioxide, is a radioactive, olive green cubic crystalline solid with the formula NpO₂. It is one of two stable oxides of neptunium, the other being neptunium(V) oxide. It emits both α- and γ-particles.