Some Important Compounds of Transition Elements

We come in contact with various transition metals on a daily basis, without even coming to realize the fact. For example, take iron. From ships and buildings, iron is used even in the cutlery around us. Some of the important compounds of transition elements are also used in our daily lives in much the same manner. Let us take a look at some of the important compounds of transition elements and study their properties as well.

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Transition Elements

Transition metals are usually defined as those elements that have or can readily form partially filled ‘d’ orbitals. The d-block elements in the groups of 3 to 11 are known as transition elements. The f block elements are also called inner transition metals, which are also known as the lanthanides and actinides. They also meet this criterion because the d orbital is only partially occupied before the f orbitals.

The d orbitals are usually filled with the copper family which is the group 11 and for this reason, the next in the family which is group 12 is technically not defined as compounds of transition elements. However, the group 12 elements surely display some of the same chemical properties and are commonly included in the discussions related to transition metals. Some chemists, however, do treat the group 12 elements as transition metals.

The d-block elements are divided into the first transition series, which are the elements Sc through Cu, the second transition series which are the elements Y through Ag, and the third transition series which are the element La and the elements Hf through Au. Actinium, Ac, is the first member of the fourth transition series, which also includes Rf through Rg. The f-block elements are the elements Ce through Lu, which usually constitute the lanthanide series, and the elements Th through Lr, which constitute the actinide series.

Learn more about Inner Transition Elements in detail here.

Lanthanum behaves very much like the lanthanide elements, which is why it is considered a lanthanide element, even though its electron configuration makes it the first member of the third transition series. Similarly, the behaviour of actinium means that it is part of the actinide series, although its electron configuration makes it the first member of the fourth transition series.

Transitions and Inner Transition Elements

Compounds of Transition Elements

Ferrous Sulphate (Green Vitriol), FeSO₄.7H­₂O

Hydrated and anhydrous FeSO4 is green and white in colour respectively. It is isomorphous with Epsom salt, MgSO₄.7H₂O and ZnSO₄.7H₂ It effervesces on exposure to air. Like other ferrous salts, it takes up HNO₃ forming brown coloured double compound, Fe(NO)SO₄, nitroso ferrous sulphate.

It forms double salts with sulphates of alkali metals with general formula R₂SO₄.FeSO₄.6H₂O. With ammonium sulphate, it forms a double salt known as ferrous ammonium sulphate or Mohr’s salt, FeSO₄.(NH4)2SO4.6H2O. It does not effervesce. It ionises in solution to gives Fe²⁺, NH⁴⁺ and SO₄^2– ions.

Ferric Oxide, Fe₂O₃

Anhydrous salt is yellow, deliquescent compound and highly soluble in H₂O. On heating, it gives FeCl₂ and Cl₂. Its aqueous solution is acidic due to hydrolysis.

Silver Nitrate, AgNO₃

Silver nitrate forms precipitate with some salt solutions which help in the detection of acid radicals. It decomposes on heating.

Mercury (I) Chloride / Mercurous Chloride / Calomel, (Hg₂Cl₂)

It is a white power insoluble in water but soluble in chlorine water. On treatment with ammonia, if turns black due to the formation of finely divided mercury.

Mercury (II) Chloride HgCl₂

It is a white crystalline solid sparingly soluble in cold water but soluble in hot water. Its solubility can be increased by adding Cl. When treated with SnCl₂ it is reduced to mercury.

Mercury-II Iodide

Mercuric iodide exists in two forms, i.e. red and yellow. The yellow form is stable above 400 K white the red form is stable below this temperature. An alkaline solution of K₂HgI₄ is called Nessler’s reagent and is used to detect the presence of NH⁴⁺ with which it gives a brown precipitate due to the formation of iodide of Million’s base.

Solved Examples for You

Question: Depict through chemical equations how the halides of transition elements react?

Answer: Anhydrous halides of each of the transition elements can be prepared by the direct reaction of the metal with halogens.

2Fe(s)+3Cl₂(g)⟶2FeCl₃(s)

Heating a metal halide with additional metal can be used to form a halide of the metal with a lower oxidation state:

Fe(s)+2FeCl₃(s)⟶3FeCl₂(s)

The preparation of stable water solutions of the halides of the metals of the first transition series is by the addition of a hydrohalic acid to carbonates, hydroxides, oxides, or other compounds that contain basic anions. NiCO₃(s)+2HF(aq)⟶NiF₂(aq)+H₂O(l)+CO₂(g)