Properties And Reactions Of Elements And Compounds of D Block Elements - Session 2

When a transition metal ion is surrounded by ligands, the interaction between metal ion and ligand causes a distortion in the symmetry of d-orbitals of metal ions. This distortion is due to the repulsion between the electrons in the d-orbitals and the electrons in the ligands. The repulsion causes the d-orbitals to split into two different energy levels. The energy levels are named t2g and eg. The t2g level has three d-orbitals with low energy. The eg level has two d-orbitals with high energy.

The symbol ∆ denotes the energy difference between t2g and eg energy levels. The energy difference ∆ between the two sets of d orbitals determines the color of the complex. When a photon of light strikes the complex, it can be absorbed by an electron in one of the t2g orbitals. The energy of the absorbed photon must be the same as the energy difference between the t2gand eg levels. The absorbed energy causes the electron to jump from the t2g level to the eg level. This results in an empty space or hole in the t2g level.

The hole in the t2g level can be filled by an electron from one of the ligands. This electron of ligand releases energy in the form of a photon of light. The energy released in this process must also be the same as the energy difference between the two d orbital energy levels. The color of the released photon is complementary to the absorbed photon, meaning that it has the opposite color. The color of released photon is the color of given coordination complex. This means if electron in d orbital absorbs red light, then color of the coordination complex will be green.

Now we shall discuss how to name the coordination complexes. As we know that in an inorganic compound, that consists of cations and anions, cation is named first. For example in sodium chloride, sodium is cation, and chloride is anion. Coordination complexes are of two types. One type consists of complex cation and simple anion. Hexaaminecobalt (III) Chloride, or [Co(NH₃)₆]Cl₃ is an example of such complexes. It consists of Hexaaminecobalt (III) Chloride cation and chloride anion.

Let’s discuss rules for naming such complexes. First of all we shall identify the central metal ion. After that we shall find the oxidation state of the central metal ion. For example, in case of hexaaminecobalt(III) cation, which is [Co(NH₃)₆]⁺³, cobalt is the central metal ion. Here, the oxidation state of cobalt is positive three. After that we shall identify the ligands. In this example, the ligand is ammonia N H three. The ligand can be neutral or negatively charged or positively charged.

For negatively charged ligands, o is added at the end of their name. For example, if ligand is chloride ion then name of the chloride will be written as chlorido. Neutral ligands have no special ending. Some of them has special names. H₂O is named as aqua. NH₃ is named as ammine. In case of positive charged ligands, ium is added at the end of their name. ⁺NH₂-NH₂ is named is hydrazinium. In [Co(NH₃)₆]⁺³, ligand is NH₃. It is a neutral ligand. It is named as ammine.

Now we shall count the number of ligands. For two, three, four, five and six ligands of the same type, we use the prefixes di, tri, tetra, penta and hexa. If more than one form of ligands are there then ligands are named in alphabetical order. Now combining all things together, we shall first write the number and name of ligand in the complex ion. After that we shall write the name of central metal ion. The name of central metal ion is written as it is. After this we shall write the oxidation state of metal ion in parentheses. The name of [Co(NH₃)₆]⁺³ is hexaaminecobalt(III) ion.

Now the name of complex cation is complete. As we know chloride anion is attached to it. So name of [Co(NH₃)₆]Cl₃ is hexaaminecobalt(III) chloride. There is another type of coordination complexes which consist of simple cation and complex anion. In such cases we shall first write name of simple cation. After this we shall follow same rules for naming complex anions as discussed before except the name of central metal ion. We shall add ate at the end of the name of central metal ion. For example, the name of Na₃[Co(CN)₆]N A three C O C N six complex is sodium hexacyanidoferrate(III).

We can also write the formula of a coordination complex from its name. We shall follow same rules that we learned. For example, lets try to write the formula of sodium tetracyanidocuprate(II) complex. As we can see sodium is the simple ion. Tetracyanidocuprate(II) is the complex ion. We shall always write the formula a of complex ion within square brackets. As we can see, tetracyanido indicates that there are four cyanide ligands. o is at the end of cyanide, which shows that cyanide is a negatively charged ligand. So there are four cyanide ligands. Ligands are written within round-brackets.

Cuprate indicates that central metal ion is copper. ate in the cuprate shows that the complex ion is anion. Two written in roman numerals after cuprate within round-bracket as (II) indicates that oxidation state of copper is positive two. We first write the symbol of metal ion. After that we write the ligand symbol within round-brackets. We also mention the number of ligands. After that we enclose both of them within square brackets.

Now we find the charge of the whole complex ion. As we know the charge on one ligand is negative one. So the overall charge of the complex anion is calculated as negative two. In our example, sodium is the cation. So, two sodium ions are written to equate the negative two charge of complex anion. The complete formula of the given coordination complex is illustrated. Can you write the formula of tetraaminecopper(II) chloride?.

The flame test is a simple analytical technique. It is used to identify ions based on the characteristic colors they produce when they are heated in a flame. In this method, a small amount of the sample containing the ion is placed in a flame. The heat of the flame causes the electrons in the ion to become excited and jump to higher energy levels. When the electrons return to their original energy levels, they release energy in the form of light. The color of the light emitted by the ion is characteristic of the ion in the sample.

To perform a flame test for ions, a small amount of the sample is first dissolved in water to form a solution. A small amount of the resulting solution is then applied to a wire-loop or a wooden stick and heated in a flame. The color of the flame produced by the ion is observed. It is then compared to known reference colors to identify the ion. Sodium ions give a yellow-orange flame color. Potassium ions give a violet flame color. Calcium ions give an orange-red color.

The brown-ring test is a chemical test used to detect the presence of nitrate ions in a solution. To perform the test, a small amount of iron sulfate FeSO₄ is added to the solution being tested. After that concentrated sulfuric acid is added carefully downward the side of the test tube. It forms a separate layer at the bottom of the tube. If nitrate ions are there in the solution, a brown-ring will form at the interface between the two layers. This indicates the presence of nitrate ions.