Electronic Configurations of d Block Elements for IIT JEE

d Block Elements or Transition Elements

Groups 3 to 12 elements are called d-block or transition elements. These elements are present between p-block and s-block elements in the periodic table. These elements’ properties are intermediate between the properties of s -block and p -block elements, i.e. d -block elements represent a change or transition in properties from most electropositive s - block elements to less electropositive p - block elements. Therefore, these elements are called transition elements.

Forty elements belong to the d-block elements. Fourth, fifth, sixth and seventh periods consist of ten elements each.
The d-block elements include the most common metals used in construction and manufacturing, metals that are valued for their beauty (gold, silver and platinum), metals used in coins (nickel, copper) and metals used in modern technology (titanium). Copper, silver, gold and iron were known and used in early civilization. 

Certain d-block elements are particularly important in living organisms. Iron, the transition element, is present in the largest quantity in the human body. The best known biological iron containing compound is the protein haemoglobin, the red component of blood that is responsible for the transport of oxygen. Cobalt is the crucial element in vitamin Bl2, a compound that acts as a catalyst in the metabolism of carbohydrates, fats and proteins. Molybdenum and iron together with sulphur form the reactive portion of nitrogenase, a biological catalyst is used by nitrogen fixing organisms to convert atmospheric nitrogen into ammonia. Copper and zinc are important in other biological catalysts. Iron, zinc, copper, cobalt, nickel, manganese and molybdenum are known to be the essential components of enzymes. Vanadium and chromium are also essential for life. Some bad elements are also present in this block. For example, mercury is toxic and is threat to the environment.

Electronic Configuration

In the transition element, the last differentiating electron is accommodated on penultimate d-orbitals, i.e., d-orbitals are successively filled. The general electronic configuration of transition elements is:

(n-1)1-10 ns0,1 or 2
There are four complete rows (called series) of ten element each corresponding to filling of 3d, 4d, 5d and 6d-orbitals respectively. Each series starts with a member of group third (IIIB) and ends with a member of group twelve (IIB).

Filling Transition Metal Orbitals

The first row transition metal electron configuration consists of 4s and 3d subshells with a core of argon (noble gas). This applies only to transition metals in the first row, adjustments are required when writing the electron configuration for the other transition metal rows. Before the first row of transition metals, the noble gas would be the core written around the element symbol with brackets (i.e. [Ar] would be used for the first row of transition metals), and the electron configuration would follow a [Ar] nsxndx format. The electron configuration for first row transition metals would simply be [Ar] 4sx3dx. Based on the periodic table, the energy level, "n," can be determined simply by looking at the row number in which the element is located. There is, however, an exception for the d-block and f-block, where the energy level, "n" for the d-block is "n-1" ("n" minus 1) and "n-2" for the f-block (see the following periodic clarification table). The "x" in nsx and ndx in this case is the number of electrons in a particular orbital (i.e. s - orbitals can hold up to 2 electrons, p - orbitals can hold up to 6 electrons, d - orbitals can hold up to 10 electrons, and f - orbitals can hold up to 14 electrons). To determine what "x" is, simply count the number of boxes you will find before you reach the element you are trying to determine the configuration of the electron.

First transition or 3d-series: 

Elements: Sc(21) to Zn(30). 3d-orbitals are gradually filled up.

ElementSymbolAt. No.Electronic configuration
ScandiumSc21[Ar] 3d142
TitaniumTi22[Ar] 3d242
VanadiumV23[Ar] 3d342
ChromiumCr24[Ar] 3d541
ManganeseMn25[Ar] 3d542
IronFe26[Ar] 3d642
CobaltCo27[Ar] 3d742
NickelNi28[Ar] 3d842
CopperCu29[Ar] 3d1041
ZincZn30[Ar] 3d1042

The actual configurations are explained on the basis of stability concept of half-filled or completely filled (n-l) d-orbitals. (n-l) d-subshell is more stable when 5 or 10 electrons are present, i.e., every d-orbital is either singly occupied or doubly occupied.

Second transition or 4d-series

This series consists of elements from Y(39) to Cd(48). 4d-orbitals are gradually filled up.

ElementSymbolAt. No.Electronic configuration
YttriumY39[Kr] 4d1 5s2
ZirconiumZr40[Kr] 4d2 5s2
Niobium Nb41[Kr] 4d4 5s1
Molybdenum Mo42[Kr] 4d5 5s1
Technetium Tc43[Kr] 4d6 5s2
Ruthenium Ru44[Kr] 4d7 5s2
Rhodium Rh45[Kr] 4d8 5s1
Palladium Pd46[Kr] 4d10 5s0
SilverAg47[Kr] 4d10 5s1
CadmiumCd48[Kr] 4d10 5s2

Elements marked with asterisk have anomalous configurations. Nuclear-electron and electron-electron forces are attributed factors.

Third transition or 5d-series: 

This series consists of elements from La(S7) to Hg(80) except 14 elements of lanthanide series from Ce(S8) to Lu(71). 5d-orbitals are gradually filled up.

ElementSymbolAt. No.Electronic configuration
Lanthanum La57[Xe] 5d1 6s2
Hafnium Hf72[Xe] 4f14 5d2 6s2
Tantalum Ta73[Xe] 4f14 5d3 6s2
Tungsten W74[Xe] 4f14 5d4 6s2
Rhenium Re75[Xe] 4f14 5d5 6s2
Osmium Os76[Xe] 4f14 5d6 6s2
Iridium Ir77[Xe] 4f14 5d7 6s2
Platinum Pt78[Xe] 4f14 5d8 6s1
Gold Au79[Xe] 4f14 5d9 6s1
MercuryHg80[Xe] 4f14 5d10 6s2

Fourth transition or 6d-series 

This series consists of elements from Ac(89) to Uub(112) except 14 elements of actinide series from Th(90) to Lr(103). 6d-orbitals are gradually filled up.

ElementSymbolAt. No.Electronic configuration
Actinium Ac89[Rn] 6d1 7s2
RutherfordiumRf104[Rn] 5f14 6d2 7s2
HahniumHa105[Rn] 5f14 6d3 7s2
SeaborgiumSg106[Rn] 5f14 6d4 7s2
BohriumBh107[Rn] 5f14 6d5 7s2
HassiumHs108[Rn] 5f14 6d6 7s2
MeitneriumMt109[Rn] 5f14 6d7 7s2
Ununnilium (Darmstadtium) Uun110[Rn] 5f14 6d8 7s2
Unununium (Rontgenium) Uuu111[Rn] 5f14 6d10 7s1
UnunbiumUub112[Rn] 5f14 6d10 7s1

The elements from atomic numbers 106 to 112 have recently been reported but these heavy elements are very unstable. It is evident from the above electronic configurations that in transition elements ns-orbital is filled before (n-1) d-orbitals. Near about atomic number 20, 4s-subshell has somewhat lower energy than 3d-subshell. Due to this, in potassium (Z = 19) and calcium (Z = 20), 4s-subshell is filledbefore 3d-subshell. Therefore, the electronic configurations of potassium and calcium are:

Potassium 19 ls22s22p63s23p64s1
Calcium 20 ls22s22p63s23p64s2

Beyond calcium, the energy of 3d-subshell is less than the energy of 4s and 4p-orbitals. Thus, 3d-orbitals are filled from scandium (Z = 21) to zinc (Z = 30). The filling of the 3d-orbitals proceeds one at a time. The d-orbitals are first occupied singly and then pairing starts. However, in two cases, chromium (Z = 24) and copper (Z = 29), one electron IS present on 4s-orbital.

The unusual filling patterns in chromium and copper lead us to conclude that half-filled and fully-filled subshells are unexpectedly stable. In the first series, 3d-electrons become more effective in shielding 4s-electrons from the nucleus, i. e., 3d-electrons suffer more attraction than 4s-electrons from nucleus. This is apparent from the fact that when atoms of the elements from atomicnumber 21 to 30 change into cations, the 4s-electrons are lost first before 3d-electrons, although 4s-subshell was filled earlier.

Mn 25 (3d54s2) Mn2+ 3d5
Fe 26 (3d64s2) Fe2+ 3d6
Ni 28 (3d84s2) Ni2+ 3d8

The same thing is repeated in second transition series, i.e., in the 5th period, the 5s-subshell is filled before 4d-subshell. In rubidium (2 = 37) and strontium (2 = 38), 5s-subshell is filled. 4d-subshell is gradually filled from yttrium (2 = 39) to cadmium(2 = 48). In 6th period, 6s-subshell is filled first before anyelectron is accommodated on 5d or 4f-orbitals. In lanthanum. (2 = 57), the energies of 4f, 5d and 6s are very close to one another and after filling 6s-orbital in caesium (2 = 55) and barium (2 = 56), the next electron in lanthanum is accommodated on 5d-orbitals. In the subsequent elements from cerium (Z=58) to lutetium (Z=71) 4f-orbitals are gradually filled. From hafnium (2 = 72), the 5d-orbitals are filled. This process is completed in mercury.

Hf: 72: 4f145d26s2
Hg: 80:4f145d106s2

Similar pattern in fourth transition series is observed. The fourteen elements following lanthanum (2 = 57) from cerium (58) to lutetium (2 = 71) constitute the first inner transition series. These are also called lanthanides. In these elements 4f-orbitals are being filled successively. Similarly, the fourteen elements following actinium (2 = 89) from thorium (2 = 90) to lawrencium (2 = 103) constitute the second inner transition series. These are also called actinides. In these elements 5f-orbitals are successively filled.