D-Block and F-Block Elements: Occurrence of the First Row Transition Metal Elements (For CBSE, ICSE, IAS, NET, NRA 2022)

Doorsteptutor material for competitive exams is prepared by world's top subject experts: get questions, notes, tests, video lectures and more- for all subjects of your exam.

Occurrence of the First Row Transition Metal Elements

  • A few of the transition elements occur in free state e. g. and .
  • Most of these elements occur as oxides, Sulphide and carbonates in nature.

D-Block Elements

  • d-Block elements occupy the middle portion of the periodic table i.e.. between s-block and p- block elements.
  • They include elements from groups 3 to 12.
  • The elements of the d-block are metallic in nature.
  • General characteristics properties are intermediate between those of the s-block elements and p-block elements.
  • These elements the outermost shell contains one or two electrons in their outer most i.e.. ns orbital, but the last electron enters into the inner d-subshell i.e.. orbital.
  • d-block elements represent a change (or transition) from the most electropositive s-block elements to the least electropositive p-block elements, therefore are also termed as transition element.
  • There are four series of transition elements in the periodic table.
  • The first transition series begins with scandium (At. No. 21) and ends at copper (At. No. 29, the second, third and fourth series begin with yttrium (At. No. 39) , lanthanum (At. No. 57) and actinium (At. No. 89) and end at silver (At. No. 47) , gold (At No. 79) and at the element having atomic number 112 (a synthetic element) , respectively.
  • These series are also referred to as , , and series, respectively.

Electronic Configuration

  • The general electronic configuration of transition elements is .
  • The stands for inner shell and the d-orbitals may have one to ten electrons and the s-orbital of the outermost shell may have one or two electrons.
Electronic Configuration
  • Fig shows that orbital is of lower energy than 3d orbitals up to potassium (At. No. 19) .
  • The energy of 3d orbitals decreases with further increase of atomic number and become lower than , and , (in case of scandium At. No. 21) .
  • Thus , after filling 4s orbitals successively with two electrons at atomic number 19 and 20, the next incoming electron goes to orbital instead of as has lower energy.
  • Nine elements following calcium, the incoming electron is filled in the d- subshell.
  • Half-filled and completely filled subshells are stabler than the one in which one electron is short, an electron gets transferred from to as in case of element of atomic number 24 and 29.
  • Due to this the configuration of chromium and copper have only one 4s electron as shown in table.

Electronic Configuration of First Series Transition Elements

Electronic Configuration of First Series
  • In zinc, the 30th electron goes to level and not level which is already full. Thus, by definition zinc cannot be called a member of d-block elements.
  • However, zinc and other members of group 12, viz. cadmium and mercury are discussed along with , and transition elements for the sake of convenience.
  • During the process of ionization, ionization electrons should be lost first from the subshells and then from the level. But this is not the case because once the filling of the subshell commences at scandium (At. No. 21) energy of subshell decreases and becomes lower than that of subshell.
  • Thus, on ionization the first-row transition elements lose electrons from the 4s subshell followed by the loss from level.
  • For example, vanadium has electronic configuration and the electronic configuration of is .

Physical Properties

  • All transition elements show typical metallic properties such as high tensile strength, ductility, malleability, high thermal and electrical conductivity and metallic lustre.
  • Transition elements show high melting and boiling points.
  • All the transition elements are hard except zinc, cadmium and mercury.
  • They show high enthalpy of atomization.
  • Density of transition elements are very high as compared to those of s-block elements.
  • The density of the elements in a given transition series increases across a period and reaches a maximum value at groups 8,9 and 10.
  • The radii of the elements decrease from left to right across a row in the transition series until near the end, then the size increases slightly.
  • On moving from left to right, extra protons are placed in the nucleus and extra electrons are added. The d-orbital electrons shield the nuclear charge poorly.
  • Thus, charge increases and, therefore, electrons are attracted more strongly, result in contraction of size of atom .
  • For example, , and .

Developed by: