chemistry

Molybdenum bronze

Molybdenum bronze 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 Molybdenum bronze rather than just read about it. In short: In chemistry, molybdenum bronze is a generic name for certain mixed oxides of molybdenum with the generic formula AxMoyOz where A may be hydrogen, an alkali metal cation (such as Li+, Na+, K+), and Tl+. These compounds form deeply coloured plate-like crystals with a metallic sheen, hence their name.

Key takeaways

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

Reference excerpt

In chemistry, molybdenum bronze is a generic name for certain mixed oxides of molybdenum with the generic formula AxMoyOz where A may be hydrogen, an alkali metal cation (such as Li+, Na+, K+), and Tl+. These compounds form deeply coloured plate-like crystals with a metallic sheen, hence their name. These bronzes derive their metallic character from partially occupied 4d bands. The oxidation states in K0.28MoO3 are K+1, O2−, and Mo+5.72. MoO3 is an insulator, with an unfilled 4d band. These compounds have been much studied since the 1980s due to their markedly anisotropic electrical properties, reflecting their layered structure. The electrical resistivity can vary considerably depending on the direction, in some cases by 200:1 or more. They are generally non-stoichiometric compounds. Some are metals and some are semiconductors.

Preparation The first report of a "molybdenum bronze" was by Alfred Stavenhagen and E. Engels in 1895. They reported that electrolysis of molten Na2MoO4 and MoO3 gave indigo-blue needles with metallic sheen, which they analysed by weight as Na2Mo5O7. The first unambiguous synthesis of alkali molybdenum bronzes was reported only in 1964, by Wold and others. They obtained two potassium bronzes, "red" K0.26MoO3 and "blue" K0.28MoO3, by electrolysis of molten K2MoO4+MoO3 at 550 °C and 560 °C, respectively. Sodium bronzes were also obtained by the same method. It was observed that at a slightly higher temperature (about 575 °C and above) only MoO2 is obtained. Another preparation technique involves crystallization from the melt in a temperature gradient. This report also called attention to the marked anisotropic resistivity of the purple lithium bronze Li0.9Mo6O17 and its metal-to-insulator transition at about 24 K. Hydrogen bronzes HxMoO3 were obtained in 1950 by Glemser and Lutz, by ambient-temperature reactions. The hydrogen in these compounds can be replaced by alkali metals by treatment with solutions of the corresponding halides. Reactions are conducted in an autoclave at about 160 °C.

Classification Molybdenum bronzes are classified in three major families:

Red bronzes with limiting composition A0.33MoO3, that is, AMo3O9: Lithium molybdenum red bronze Li0.33MoO3 Reau and others. Potassium molybdenum red bronze K0.26Mo1.02O3 or K0.3MoO3 Cesium molybdenum red bronze Cs0.33MoO3 Potassium molybdenum red bronze K0.23Mo1.01O3 a semi-conductor. Blue bronzes, with limiting composition A0.30MoO3, that is, A3Mo10O30. Their electronic properties generally do not depend on the metal A. Potassium molybdenum blue bronze K0.28Mo1.02O3 or K0.3MoO3 Rubidium molybdenum blue bronze Rb0.3MoO3 Thallium molybdenum blue bronze Tl0.3MoO3 Purple bronzes, generally with limiting formula A0.9Mo6O17. Their electronic properties depend strongly on the metal A. Lithium molybdenum purple bronze Li0.9Mo6O17 Sodium molybdenum purple bronze Na0.9Mo6O17 Potassium molybdenum purple bronze K0.9Mo6O17 Rubidium molybdenum purple bronze Rb0.9Mo6O17 Thallium molybdenum purple bronze Cs0.9Mo6O17 The hydrogen molybdenum bronzes have similar appearances but different compositions:

Hydrogen molybdenum orthorhombic blue bronze HxMoO3, 0.23 < x < 0.4 Hydrogen molybdenum monoclinic blue bronze HxMoO3, 0.85 < x < 1.4 Hydrogen molybdenum red bronze HxMoO3, 1.55 < x < 1.72 Hydrogen molybdenum green bronze H2MoO3 or MoO2.H2O Other molybdenum bronzes with anomalous electrical properties have been reported, which do not fit in these families. These include

Tetragonal KMo4O6 KxMoO2−δ.

See also Sodium tungsten bronze – Chemical intercalation compound

Notes

References

Worked examples

Example 1 — a first encounter with Molybdenum bronze

Start with the simplest possible case. Write down what Molybdenum bronze 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 Molybdenum bronze 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 Molybdenum bronze 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 Molybdenum bronze

In research: Molybdenum bronze 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 Molybdenum bronze 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: Molybdenum bronze is common in secondary-school and first-year university syllabi. It links to neighbouring topics Molybdenum compounds, Non-stoichiometric compounds, Transition metal oxides, so understanding it makes those chapters shorter.
In everyday life: Look for Molybdenum bronze 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 Molybdenum bronze in 20 minutes

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

Frequently asked questions

What is Molybdenum bronze in simple terms?

Why does Molybdenum bronze 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 Molybdenum bronze?

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 Molybdenum bronze.