chemistry

Phosphorus selenide

Phosphorus selenide 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 Phosphorus selenide rather than just read about it. In short: Phosphorus selenides are a relatively obscure group of compounds. There have been some studies of the phosphorus - selenium phase diagram and the glassy amorphous phases are reported.

Key takeaways

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

Reference excerpt

Phosphorus selenides are a relatively obscure group of compounds. There have been some studies of the phosphorus - selenium phase diagram and the glassy amorphous phases are reported. The compounds that have been reported are shown below. While some of phosphorus selenides are similar to their sulfide analogues, there are some new forms, molecular P2Se5 and the polymeric catena-[P4Se4]x. There is also some doubt about the existence of molecular P4Se10.

Crystallographically confirmed compounds

P2Se5 Molecular P2Se5 has a norbornane like structure with two phosphorus atoms with oxidation state +3 bridged by two diselenide units (−Se−Se−, analogous to disulfide) and one selenide unit (−Se−). It was isolated by solvent (CS2) extraction from a P2Se5 amorphous phase made from the elements.

P4Se3 P4Se3 has been characterised crystallographically and has the same structure as the low temperature form of P4S3. It can be prepared from the elements. One preparation is to extract and recrystallise using tetralin.

P4Se5 The P4Se5 molecule has the same structure as P4S5. It was prepared by reacting P4Se3 with bromine in CS2.

catena-[P4Se4]x This compound consists of polymeric chains of norbornane-like units joined by Se atoms. As each P atom in the repeat unit is bonded to another P atom and to two Se atoms, each P atom has a formal oxidation state of +2.

Compounds confirmed spectroscopically

P4Se4 P4Se4 has two crystalline forms α-P4Se4 with the same molecular structure as α-P4S4 and β-P4Se4 with same molecular structure as β-P4S4. A fully characterised compound (CuI)3P4Se4 contains P4Se4 with a β-P4S4 structure.

P4Se7 This has been reported to have the same structure as P4S7. One well-known textbook does not mention it at all.

P4Se10 Molecular P4Se10 has been reported to share the same structure as P4S10 and P4O10, but one well-known textbook does not mention it at all. A review (2001) examining P-Se amorphous phases did not confirm the presence of molecular P4Se10. The isoelectronic anion [Ge4Se10]4− which has the adamantane like P4O10 structure is known, an example is the sodium salt Na4[Ge4Se10].

Other compounds P4Se6, P14Se, P4Se, P4Se2, P2Se, have been reported.

Phosphorus - selenium glasses Phosphorus - selenium glasses have been examined using 31P-NMR and Raman spectroscopy. Glasses are formed in PxSe1−x over the range of compositions 0 < x < 0.8 with a small window around 0.52 – 0.60 centred on 0.57 (corresponding to the compound P4Se3) where there is a tendency to crystallise. For x < 0.47 the glasses contain Sen chain fragments, pyramidal P units (P oxidation state +3), quasi-tetrahedral P units (P oxidation state +5, with P=Se double bond) and P2 units (P in formal oxidation state +4). There is no evidence for an amorphous phase containing molecular P4Se10.

References

Worked examples

Example 1 — a first encounter with Phosphorus selenide

Start with the simplest possible case. Write down what Phosphorus selenide 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 Phosphorus selenide 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 Phosphorus selenide 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 Phosphorus selenide

In research: Phosphorus selenide 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 Phosphorus selenide 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: Phosphorus selenide is common in secondary-school and first-year university syllabi. It links to neighbouring topics Inorganic phosphorus compounds, Selenides, so understanding it makes those chapters shorter.
In everyday life: Look for Phosphorus selenide 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 Phosphorus selenide in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Phosphorus selenide 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 Phosphorus selenide out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Phosphorus selenide in simple terms?

Phosphorus selenides are a relatively obscure group of compounds. There have been some studies of the phosphorus - selenium phase diagram and the glassy amorphous phases are reported.

Why does Phosphorus selenide 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 Phosphorus selenide?

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 Phosphorus selenide.