Properties And Reactions Of Elements And Compounds of D Block Elements - Session 1

Transition elements are a group of chemical elements found in the middle of the periodic table. They are also known as transition metals because they have unique properties that allow them to transition from one state to another.They reside between s and p block elements. Transition elements include d block elements and f block elements. The last electron in d block elements enters d orbital. The last electron in f block elements enters f orbital. Some examples of d block transition elements include iron, copper, nickel, and zinc.

One of the most important properties of transition elements is their ability to form ions with different charges. This is because they have electrons in their outermost energy level that are not tightly bound to the atom. These electrons can be easily lost or gained, leading to the formation of different ions with varying charges. For example Tillurium can form ions with different oxidation states. It can form Ti⁺³ and Ti⁺⁴ ion ions.

The d block elements, also known as transition metals, are known for their catalytic activity. This means that they can speed up chemical reactions without being consumed. One example of this is the use of iron in the Haber process. Haber process is used to produce ammonia from nitrogen and hydrogen gases. The iron acts as a catalyst to speed up the reaction. It allows the reaction to occur at lower temperatures and pressures than would otherwise be required.

D-block elements have catalytic activity because of their unique electronic configuration. They have partially filled d-orbitals, which allow them to form temporary bonds with other molecules. This property enables them to interact with other molecules and facilitate chemical reactions by lowering the activation energy required for the reaction to occur. In addition, the d-block elements often have multiple oxidation states. This property makes them particularly effective in redox reactions.

Coordination complexes are molecules that contain a central metal atom or ion that is surrounded by other molecules or ions called ligands. They are also known as coordination compounds. Coordination complexes are formed by the transition metals. The ligands form coordinate bonds with the metal ion. An example of a coordination complex is [Fe(H₂O)₆]⁺². It contains an Fe⁺²ion in the centre surrounded by six H₂O molecules.

The water molecules form coordinate bonds with the iron ion by donating a pair of electrons to the iron to form a stable complex. The coordination number of metal ion in a coordination complex is the number of ligands that surround the central metal ion. Coordination number of iron in [Fe(H₂O)₆]⁺² is six. This is because central iron ion is surrounded by six water ligands.

As we know that ligands are the molecules or ions that surround the central metal ion and form coordinate covalent bond with it. A ligand can form more than one coordinate covalent bonds. It depends on the number of lone pair of electrons that a ligand can donate. When a ligand can only donate one lone pair of electrons, it is called monodentate ligand. An example of monodentate ligand is ammonia.

When a ligand can donate two lone pair of electrons to form two coordinate covalent bonds with central metal ion, it is called bidentate ligand. An example of bidentate ligand is ethylenediamine. As we can see one molecule of ethylenediamine contains two lone pair of electrons. Ethylenediamine coordinates through two NH₂ with central copper ion in bis−(ethylenediamine)cuprate(II) complex. Therefore it is a bidentate ligand.

When a ligand can donate more than two lone pair of electrons to form covalent bonds with central metal ion, it is called polydentate ligand. An example of polydentate ligand is ethylenediaminetetraacetate. Ethylenediaminetetraacetate has six coordination sites. It is a polydentate ligand.

The complex formed when a bidentate or polydentate ligand combines with a metal ion is called Chelate. The process of formation of chelate is called chelation. The ligand that forms chelate is called chelating ligand. Bidentate and polydentate ligands are called chelating ligands.For example, bis−(ethylenediamine)cuprate(II) ion is a chelate. It is formed when two ethylenediamine molecules attach with copper ion. Ethylenediamine is a bidentate ligand.

Oxides of the d block elements might exhibit acidic or basic or amphoteric nature based on the oxidation state of metal ion. If the oxidation state of metal ion in a d block metal oxide is low, then metal oxide is basic in nature. For example, Manganese oxide MnO is basic in nature. This is because oxidation state of manganese in MnO is positive two. It is lowest oxidation state of manganese.

If the oxidation state of metal ion in a d block metal oxide is high, then metal oxide is acidic in nature. For example, Manganese heptoxide Mn₂O₇ is acidic in nature. This is because oxidation state of manganese in Mn₂O₇ is positive seven. It is the highest oxidation state of manganese. Can you identify which oxide of vanadium will be more acidic ?Vanadium monoxide VO or vanadium pentaoxide V₂O₅ ?

If the oxidation state of metal ion in a d block metal oxide is intermediate between its lowest and highest oxidation states, then metal oxide is amphoteric in nature. For example, Manganese dioxide MnO₂ is amphoteric in nature. It means it can behave both as an acid as well as base.This is because oxidation state of manganese in MnO₂ is positive four. It is intermediate between lowest and highest oxidation states of manganese.