Urgent Notes

Transition elements

What are the transition elements?

The elements which lie in-between s and p block elements in the periodic table are called transition elements the properties of these elements are between those of s and p block elements.
transition elements may be defined as the element whose atom or ice contain partially filled d orbital but the definition does not cover Zn, Cd and Hg which are not included in transition elements due to similarity in properties with these elements.
Hindi elements the last electron enter in the orbital therefore they are also called d block elements

Classification of transition elements

First transaction series or 3D series: it consists of 10 elements of the fourth period
Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn.
Second transition series of 4D series: it consists of 10 elements of 5th period
Zn, Nb, Mo, Rn, Rh, Pd, Ag, Of.
Third transition series of 5D series: it consists of 10 elements of the sixth period
Le, Hf, Ta, W, Re, Is, Ir, Pt, Au, Hg.
Fourth transition series or 6d series: it consists of 10 elements of the seventh period
Ac, Rf, Db, Sf, Bh, Ha, Mt, Uun, Uuu, Uub

General electronic configuration of d block elements (n-1)d¹-¹0ns0-2

Expectational configuration of Cr and Cu: that 3D level of Cr gets exactly half filled configuration and that in case of Cu it gets completely filled configuration this is explained on the basis that exactly half filled of completely filled d orbital are relatively more stable than the The other d orbital

General electronic characteristic of d block elements
Metallic characters due to low ionization all transition elements are metallic in nature if we move left to right in periodic table metallic character decreases jewellery as metallic Bond are strong IND as metals this is because they having large number of valence electron and greater effective nuclear charge greater the unpaired electrons pongal the metallic Bond hands Cr, MO ,and w are hard metal due to maximum number of unpaired electron where is Zn, Cd ,and Hg are not very hard metal total absence of unpaired electrons.

metallic points metallic points of transition Element rise to maximum and then fall as the atomic number increases.
edge greater the number of unpaired electrons strongest is the metal born and does element shows higher metallic points has metallic point first increases as the number of unpaired electron increase and then it degrees due to increase in unpaired electrons.
Mn And Tc have abnormally low melting point is due to their stable configuration the element of group 12 (Zn, CD and Hg) and have low melting points as they have no unpaired electrons.

Atomic and ionic radii
1. the atomic radii of the block elements in series generally decreases with increase atomic number but decrease in atomic radii because small after Midway example for that element of first transition series the atomic radii gradually from Sc to Cr but from Cr to see you it remain constant.


The atomic radius decreases in a period in beginning with the increase in atomic number nuclear charge goes on increasing the electron are added anti orbital which screen the outermost electrons therefore as the number of free electron increases the second in effect of increasing this utilizes the effect of increased their charge with the increase in atomic number are atomic radii remain unchanged.
2. at the end of which period there is a slight increase in atomic radii because near the end of series the electron electron repulsion between the electron increase as a result expansion of election of cloud takes place and the atomic radii increases.

4. Density: the density of transition elements as we move from left to right in the series this is because along the series the atomic radius decreases and atomic volume also decrease and does density increases example Sc has lowest density among transition elements.
oxidation state the transition elements such a large number of oxidation State this is due to the participation of inner electrons in addition to the outer electron because the energy of ns and and(n-1)d subshells are almost equal the highest oxidation States found in compound in f and it is due to small size and high electronegativity of F and O atom.
the transition elements generally shows + 2 and + 3 oxidation State when they form ionic bond where is in higher oxidation state they form covalent bond.

6. Catalyst properties the transition elements generally shows catalyst properties because
(A) the transition elements show variable valency the form unstable intermediate compound and provide a new path with lower activation energy for the reaction (intermediate compound formation theory).
(B) transition metals also provide suitable surface for the reaction to take place the extent are absorbed on the surface of catalyst where the reaction occurs (adsorption theory).
For example



Coloured ions: the colour of transition metals is due to the presence of incomplete the orbital the d orbital split into two sets of orbital having slightly different energy this is called crystal field splitting the electron jumps from lower energy orbital to high energy d orbital within the same subshell
when a wavelength of white light is observed and rest of of them are transmitted has the salts of transition elements appear coloured.
Example
Cu²: bluish green
Sc³+ and Ti⁴+ are colourless because they have completely empty d orbital
Cu1+, Zn²+, Ag 1+, Cd2+, Hg²+ are also colourless because they have completely filled d-orbital.