chemistry

Zinc compounds

Zinc compounds 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 Zinc compounds rather than just read about it. In short: Zinc compounds are chemical compounds containing the element zinc which is a member of the group 12 of the periodic table. The oxidation state of zinc in most compounds is the group oxidation state of +2.

Key takeaways

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

Reference excerpt

Zinc compounds are chemical compounds containing the element zinc which is a member of the group 12 of the periodic table. The oxidation state of zinc in most compounds is the group oxidation state of +2. Zinc may be classified as a post-transition main group element with zinc(II). Zinc compounds are noteworthy for their nondescript appearance and behavior: they are generally colorless (unlike compounds of other elements with oxidation number +2, which are colored), do not readily engage in redox reactions, and generally adopt symmetrical structures.

General characteristics In its compounds, Zn2+ ions have an electronic configuration [Ar] 3d10. As such, Zn2+ tends to have a symmetrical coordination geometry in both its complexes and compounds. In both ZnO and ZnS, (zincblende) zinc is bound tetrahedrally bound to four ligands (oxide and sulfide, respectively). Many complexes, such as ZnCl42−, are tetrahedral. Tetrahedrally coordinated zinc is found in metallo-enzymes such as carbonic anhydrase. Six-coordinate octahedral complexes are also common, such as the aquo complex [Zn(H2O)6]2+, which is present when a zinc salts are dissolved in water. Five- and seven-coordination numbers can be imposed by special organic ligands. Many zinc(II) salts are isomorphous (have the same type of crystal structure) with the corresponding salts of magnesium(II). This parallel results from the fact that Zn2+ and Mg2+ have almost identical ionic radii as well as filled electron shells. That two elements so different in atomic number have the same radius is a consequence of the d-block contraction. Whilst calcium is somewhat larger than magnesium, there is a steady decrease in size as atomic number increases from calcium to zinc. Zn(II) complexes are kinetically labile, i.e. the Zn-ligand bonds exchange with other ligands rapidly. For this reason, zinc ions are at the catalytic centers in many enzymes.

Zn(I) Compounds with zinc in the oxidation state +1 are extremely rare. The compounds have the formula RZn2R and they contain a Zn — Zn bond analogous to the metal-metal bond in mercury(I) ion, Hg22+. In this respect zinc is similar to magnesium where low-valent compounds containing a Mg — Mg bond have been characterised.

Other oxidation states No compounds of zinc in oxidation states other than +1 or +2 are known. Calculations indicate that a zinc compound with the oxidation state of +4 is unlikely to exist.

Colour and magnetism

Zinc compounds, like those of main group elements, are mostly colourless. Exceptions occur when the compound contains a coloured anion or ligand. However, zinc selenide and zinc telluride are both coloured due to charge-transfer processes. Zinc oxide turns yellow when heated due to the loss of some oxygen atoms and formation of a defect structure. Compounds containing zinc are typically diamagnetic, except in cases where the ligand is a radical.

Reactivity of metallic zinc Zinc is a strong reducing agent with a standard redox potential of −0.76 V. Pure zinc tarnishes rapidly in air, rapidly forming a passive layer. The composition of this layer can be complex, but one constituent is probably basic zinc carbonate, Zn5(OH)6CO3. The reaction of zinc with water is slowed by this passive layer. When this layer is corroded by acids such as hydrochloric acid and sulfuric acid, the reaction proceeds with the evolution of hydrogen gas.

Zn + 2 H+ → Zn2+ + H2 Zinc reacts with alkalis as with acids. With oxidants such as chalcogens and halogens, Zn forms binary compounds such as ZnS and ZnCl2.

Binary compounds

Zinc oxide, ZnO, is the most important manufactured compound of zinc, with a wide variety of uses. It crystallizes with the Wurtzite structure. It is amphoteric, dissolving in acids to give the aqueous Zn2+ ion and in alkali to give the zincate (a.k.a. tetrahydroxozincate) ion, [Zn(OH)4]2−. Zinc hydroxide, Zn(OH)2 is also amphoteric. Zinc sulfide, ZnS, crystallizes in two closely related structures, the zincblende crystal structure and the Wurtzite crystal structure, which are common structures of compounds with the formula MA. Both Zn and S are tetrahedrally coordinated by the other ion. A useful property of ZnS is its phosphorescence. The other chalcogenides, ZnSe and ZnTe, have applications in electronics and optics. Of the four zinc halides, ZnF2 has the most ionic character, whereas the others, ZnCl2, ZnBr2, and ZnI2, have relatively low melting points and are considered to have more covalent character. The pnictogenides Zn3N2 (notable for its high melting point), Zn3P2, Zn3As2 and Zn3Sb2, have various applications. Other binary compounds of zinc include zinc peroxide ZnO2, zinc hydride ZnH2, and zinc carbide ZnC2.

Salts Zinc nitrate Zn(NO3)2 (used as oxidizing agent), zinc chlorate Zn(ClO3)2, zinc sulfate ZnSO4 (known as "white vitriol"), zinc phosphate Zn3(PO4)2 (used as primer pigment), zinc molybdate ZnMoO4 (used as white pigment), zinc chromate ZnCrO4 (one of the few colored zinc compounds), zinc arsenite Zn(AsO2)2 (colorless powder) and zinc arsenate octahydrate Zn(AsO4)2•8H2O (white powder, also referred to as koettigite) are a few examples of other common inorganic compounds of zinc. The latter two compounds are both used in insecticides and wood preservatives. One of the simplest examples of an organic compound of zinc is zinc acetate Zn(O2CCH3)2, which has several medicinal applications. Zinc salts are usually fully dissociated in aqueous solution. Exceptions occur when the anion can form a complex, such as in the case of zinc sulfate, where the complex [Zn(H2O)n(SO4] may be formed, (log K = ca. 2.5).

Complexes

The most common structure of zinc complexes is tetrahedral. Nevertheless, octahedral complexes comparable to those of the earlier transition metals are not rare. Zn2+ is a class A acceptor in the classification of Ahrland, Chatt and Davies, and so forms stronger complexes with the first-row donor atoms oxygen or nitrogen than with second-row sulfur or phosphorus. In terms of HSAB theory Zn2+ is a hard acid. In aqueous solution an octahedral complex, [Zn(H2O)6]2+ is the predominant species. Aqueous solutions of zinc salts are mildly acidic because the aqua-ion is subject to hydrolysis with a pKa of around 9, depending on conditions.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Zinc compounds

Start with the simplest possible case. Write down what Zinc compounds 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 Zinc compounds 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 Zinc compounds 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 Zinc compounds

In research: Zinc compounds 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 Zinc compounds 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: Zinc compounds is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chemical compounds by element, Zinc compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Zinc compounds 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 Zinc compounds in 20 minutes

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

Frequently asked questions

What is Zinc compounds in simple terms?

Why does Zinc compounds 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 Zinc compounds?

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 Zinc compounds.