chemistry

Nickel compounds

Nickel 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 Nickel compounds rather than just read about it. In short: Nickel compounds are chemical compounds containing the element nickel which is a member of the group 10 of the periodic table. Most compounds in the group have an oxidation state of +2.

Key takeaways

Nickel 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 Nickel compounds to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Nickel compounds from memory before moving on to harder problems.

Reference excerpt

Nickel compounds are chemical compounds containing the element nickel which is a member of the group 10 of the periodic table. Most compounds in the group have an oxidation state of +2. Nickel is classified as a transition metal with nickel(II) having much chemical behaviour in common with iron(II) and cobalt(II). Many salts of nickel(II) are isomorphous with salts of magnesium due to the ionic radii of the cations being almost the same. Nickel forms many coordination complexes. Nickel tetracarbonyl was the first pure metal carbonyl produced, and is unusual in its volatility. Metalloproteins containing nickel are found in biological systems. Nickel forms simple binary compounds with non metals including halogens, chalcogenides, and pnictides. Nickel ions can act as a cation in salts with many acids, including common oxoacids. Salts of the hexaaqua ion (Ni · 6 H2O2+) are especially well known. Many double salts containing nickel with another cation are known. There are organic acid salts. Nickel can be part of a negatively charged ion (anion) making what is called a nickellate. Numerous quaternary compounds (with four elements) of nickel have been studied for superconductivity properties, as nickel is adjacent to copper and iron in the periodic table can form compounds with the same structure as the high-temperature superconductors that are known.

Colour Most of the common salts of nickel are green due to the presence of hexaaquanickel(II) ion, Ni(H2O)62+.

Geometry Nickel atoms can connect to surrounding atoms or ligands in a variety of ways. Six coordinated nickel is the most common and is octahedral, but this can be distorted if ligands are not equivalent. For four coordinate nickel arrangements can be square planar, or tetrahedral. Five coordinated nickel is rarer.

Magnetism Some nickel compounds are ferromagnetic at sufficiently low temperatures. In order to show magnetic properties the nickel atoms have to be close enough together in the solid structure.

Binary compounds A binary compound of nickel contains one other element. Substances that contain only nickel atoms are not actually compounds. In a noble gas matrix, nickel can form dimers, a molecule with two nickel atoms: Ni2. Ni2 has a bonding energy of 2.07±0.01 eV. For Ni2+ the bond energy is around 3.3 eV. Nickel dimers and other clusters can also be formed in a gas and plasma phase by shooting a powerful laser at a nickel rod in cold helium gas.

Oxides Nickel oxides include Nickel(II) oxide and Nickel(III) oxide.

Hydroxides Nickel hydroxides are used in nickel–cadmium and Nickel–metal hydride batteries. Nickel(II) hydroxide Ni(OH)2, the main hydroxide of nickel is coloured apple green. It is known as the mineral theophrastite. β-NiO(OH) is a black powder with nickel in the +3 oxidation state. It can be made by oxidising nickel nitrate in a cold alkaline solution with bromine. A mixed oxidation state hydroxide Ni3O2(OH)4 is made if oxidation happens in a hot alkaline solution. A Ni4+ hydroxide: nickel peroxide hydrate NiO2 · H2O, can be made by oxidising with alkaline peroxide. It is black, and unstable and oxidises water.

Halides

Nickel(II) fluoride NiF2 is yellow, crystallising in the rutile structure and can form a trihydrate, NiF2·3H2O. A tetrahydrate also exists. Nickel(III) fluoride NiF3 and Nickel(IV) fluoride NiF4 also exist. Nickel chloride NiCl2 is yellow, crystallising in the cadmium chloride structure. It can form a hexahydrate, NiCl2·6H2O, a tetrahydrate NiCl2·4H2O over 29 °C and a dihydrate, NiCl2·2H2O over 64 °C. Ammine complexes like hexaamminenickel chloride also exist. Nickel bromide NiBr2 is yellow, also crystallising in the cadmium chloride structure. It can form a hexahydrate, NiBr2·6H2O. Crystallisation above 29° forms a trihydrate NiBr2·3H2O, and a dihydrate NiBr2·2H2O. Nonahydrate, NiBr2·9H2O can crystallise from water below 2 °C. Nickelous hexammine bromide Ni(NH3)6Br2is violet or blue. It is soluble in boiling aqueous ammonia, but is insoluble in cold. Diammine, monoammine, and dihydrazine nickel bromides also exist. With four bromide atoms, nickel(II) forms a series of salts called tetrabromonickelates. Nickel iodide NiI2 is black, also crystallising in the cadmium chloride structure. It can form a green hexahydrate, NiI2·6H2O. Nickel iodide has a brown diammine NiI2•2NH3 and a bluish-violet hexammine NiI2•6NH3.

Chalcogenides

By reacting nickel with chalcogens, nickel sulfide, nickel selenide, and nickel telluride are formed. There are numerous sulfides: Ni1.5S, Ni17S18, Ni3S2 (heazlewoodite), Ni3S4 (polydymite), Ni9S8 (godlevskite), NiS (millerite) and two other NiS forms, NiS2 (vaesite) in pyrite structure. Black nickel tetrasulfide NiS4 is formed from ammonium polysulfide and nickel in water solution. Mixed and double sulfides of nickel also exist. Nickel with selenium forms several compounds Ni1−xSe 0≤x≤0.15, Ni2Se3, NiSe2 also known as a mineral penroseite. Nickel forms two different polonides by heating nickel and polonium together: NiPo and NiPo2.

Pnictides

Non-stoichiometric compounds of nickel with phosphorus, arsenic and antimony exist, and some are found in nature. One interstitial nitride has formula Ni3N (hexagonal P6322, Z = 2, a = 4.6224 Å and c = 4.3059 Å). In a solid nitrogen matrix, nickel atoms combine with nitrogen molecules to yield Ni(N2)4. Nickel phosphide Ni2P has density 7.33 and melts at 1100 °C. The mineral Nickelskutterudite has formula NiAs2-3, nickeline has formula NiAs and breithauptite has formula NiSb. NiAs melts at 967° and has density 7.77. NiSb melts at 1174°. It has the highest density of a nickel compound at 8.74 g/cm3. NiAsS gersdorffite, and NiSbS ullmannite, NiAsSe Jolliffeite are pnictide/chalcogenide compounds that occur as minerals.

Other Nickel also forms carbides and borides. Nickel borides include forms Ni2B (a green/black solid), NiB, Ni3B, o-Ni4B3 and m-Ni4B3. Nickel hydride NiH is only stable under high pressures of hydrogen. Nickel silicides include Ni3Si, Ni31Si12, Ni2Si, Ni3Si2, NiSi and NiSi2. Nickel silicides are used in microelectronics.

Diatomic molecules Hot nickel vapour reacting with other atoms in the gas phase can produce molecules consisting of two atoms. These can be studied by their emission spectrum. The nickel monohalides are well studied.

Alloys

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Nickel compounds

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

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

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

Frequently asked questions

What is Nickel compounds in simple terms?

Nickel compounds are chemical compounds containing the element nickel which is a member of the group 10 of the periodic table. Most compounds in the group have an oxidation state of +2.

Why does Nickel 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 Nickel 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 Nickel compounds.