chemistry

Neptunium sulfides

Neptunium sulfides is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Neptunium sulfides rather than just read about it. In short: Neptunium sulfides are compounds of neptunium and sulfur. In these compounds, neptunium has an oxidation state of +3 or +4, and sulfur exists as sulfide or polysulfide ions.

Key takeaways

Neptunium sulfides belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Neptunium sulfides to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Neptunium sulfides from memory before moving on to harder problems.

Reference excerpt

Neptunium sulfides are compounds of neptunium and sulfur. In these compounds, neptunium has an oxidation state of +3 or +4, and sulfur exists as sulfide or polysulfide ions. They have the general formula NpxSy. Known neptunium sulfides include NpS, Np3S4, Np2S3, Np3S5, NpS2, Np2S5, and NpS3. These compounds are often isostructural with their corresponding uranium or plutonium compounds. Neptunium oxysulfides (mixed oxide-sulfides) are also known, including Np2O2S, Np4O4S3, and NpOS.

Neptunium(III) sulfides

Neptunium monosulfide

Neptunium monosulfide has the formula NpS. It features neptunium in the +3 state, being an electride salt like plutonium monosulfide. Like plutonium monosulfide, it adopts a rock salt structure, with lattice constant a=5.532 Å. It can be produced by reducing Np2S3 with neptunium metal at 1600 °C:

Np2S3 + Np → 3 NpS It can also be produced by reacting neptunium metal with sulfur gas:

Np + S → NpS It behaves as a resistor, with an electrical resistivity of 60,000 μΩ⋅cm. It is predicted to undergo a phase transition to a caesium chloride-type structure at 75 GPa, with a 3.7% volume loss from the NaCl-type structure.

Neptunium sesquisulfide

Neptunium sesquisulfide has the formula Np2S3. It has several polymorphs, which are isostructural with the corresponding plutonium sulfides. It is often hypostoichiometric, with compositions ranging between Np3S4, Np5S7, and Np2S3. It was first prepared by reacting neptunium dioxide with carbon disulfide and hydrogen sulfide in 1948. It can also be prepared via thermal composition of Np3S5 at ~1200 K in vacuum:

2 Np3S5 → 3 Np2S3 + S Np2S3 was initially reported to be isostructural with uranium sesquisulfide (dubbed η-Np2S3) with lattice parameters a=10.3, b=10.6, and c=3.9 Å. However, later experiments could not reproduce these results. Later experiments found evidence for three polymorphs of Np2S3: α-, β-, and γ-Np2S3. These are isostructural with the corresponding plutonium compounds. α-Np2S3 is the form of Np2S3 present at standard temperature. It has an α-Ce2S3-type structure. Unlike β-Np2S3 and γ-Np2S3, it is stoichiometric. It is orthorhombic with lattice parameters a=3.98, b=7.39, and c=15.50 Å. β-Np2S3 can be formed from heating α-Np2S3 to around ~1500 K. It has a β-Ce2S3-type structure, being tetragonal with lattice parameters a=14.94, b=7.39, and c=19.84 Å. It has a stoichiometry between Np5S7 and Np2S3-ε. γ-Np2S3 can be formed from heating β-Np2S3 to around ~1800 K. It adopts the cubic Th3P4-type structure, being cubic with lattice parameter a=8.440 Å. It has a stoichiometry between Np3S4 and Np2S3-ε.

Neptunium(III,IV) sulfides

Trineptunium pentasulfide

Trineptunium pentasulfide has the formula Np3S5. Like the corresponding neptunium selenide, Np3Se5, it is antiferromagnetic, undergoing magnetic ordering at 35 K. It is a black solid which is isostructural with triuranium pentasulfide. It can be obtained by the thermal decomposition of neptunium trisulfide at 500 °C or by reacting neptunium and sulfur in caesium chloride flux. It decomposes into α-Np2S3 at 900 °C. At normal temperatures, however, it is highly stable, and is a common byproduct of reactions involving compounds of neptunium and sulfur. It contains NpIII and NpIV ions in a 2:1 ratio, and its formula can be represented as (Np3+)2(Np4+)(S2−)5.

Neptunium(IV) sulfides

Neptunium disulfide Neptunium disulfide has the formula NpS2. Very little information about it is available, and it is difficult to synthesize. Mössbauer spectroscopy indicates that it contains NpIV.

Dineptunium pentasulfide

Dineptunium pentasulfide has the formula Np2S5. It is isostructural with the corresponding thorium sulfide (Th2S5) and uranium sulfide (U2S5). It is a polysulfide, and its formula can be represented as (Np4+)2(S2−)3(S2−2). It forms tetragonal crystals, with lattice parameters a=10.48 and c=9.84 Å. It can be synthesized by reacting Np3S5 with sulfur at 500 °C:

2 Np3S5 + 5 S → 3 Np2S5

Neptunium trisulfide Neptunium trisulfide has the formula NpS3. It has been found to undergo magnetic ordering at low temperatures (~45 K). It is a polysulfide, and its formula can be represented as (Np4+)(S2−)(S2−2). It can be formed via the reaction of neptunium and sulfur at 500 °C:

Np + 3 S → NpS3 It has a monoclinic structure, isostructural with US3, with lattice parameters a=5.36, b=3.87, c=18.10 Å, and β=99°.

Neptunium oxysulfides

Np2O2S Dineptunium dioxide monosulfide (Np2O2S) is the only stable oxysulfide of neptunium at high temperatures (~1600 °C). It is isostructural with other lanthanide and actinide oxysulfides, like La2O2S, having a hexagonal crystal structure with lattice parameters a=3.95 and c=6.80 Å. It is formed by the high temperature decomposition of Np4O4S3. It contains NpIII.

Np4O4S3 Tetraneptunium tetroxide trisulfide (Np4O4S3) is formed from the decomposition of NpOS in vacuum at 700 °C. It is isostructural with Pu4O4S3, having a pseudo-hexagonal structure with lattice parameters a=4.07, b=6.76, c=3.89 Å, and β=118°. It contains NpIII and NpIV in equal amounts. Its formula can be written as (Np3+)2(Np4+)2(O2−)4(S2−)3.

NpOS Neptunium monoxide monosulfide (NpOS) is commonly encountered as a result of oxidation of other neptunium sulfides, e.g. Np3S5. Pure NpOS can be formed by oxidizing NpS in a sealed ampoule at 700 °C:

2 NpS + O2 → 2 NpOS It is isostructural with the corresponding uranium oxysulfide and plutonium oxysulfide, forming tetragonal crystals with lattice parameters a=3.815 and c=6.623 Å. It contains NpIV.

References

Illustrations

Worked examples

Example 1 — a first encounter with Neptunium sulfides

Start with the simplest possible case. Write down what Neptunium sulfides claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Neptunium sulfides before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Neptunium sulfides ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Neptunium sulfides

In research: Neptunium sulfides appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Neptunium sulfides in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Neptunium sulfides is common in secondary-school and first-year university syllabi. It links to neighbouring topics Neptunium compounds, Sulfides, so understanding it makes those chapters shorter.
In everyday life: Look for Neptunium sulfides outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Neptunium sulfides in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Neptunium sulfides means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Neptunium sulfides out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Neptunium sulfides in simple terms?

Neptunium sulfides are compounds of neptunium and sulfur. In these compounds, neptunium has an oxidation state of +3 or +4, and sulfur exists as sulfide or polysulfide ions.

Why does Neptunium sulfides matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Neptunium sulfides?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Neptunium sulfides.