1. 1 d-block elements/Transition elements The transition elements may broadly be defined as those which either as elements or ions have partly filled d- or f- sub shells. The differentiating electron enters into the (n—1) d-sub energy level then those elements are known as d-block elements. There are three series of elements in the periodic table in which 3d, 4d, 5d shells are filled by elements 6d series are incomplete series and these three series of elements together are known as d-block elements.  These elements are often called as transition elements because they are in between s-block and p-block elements, show transition from highly reactive metallic elements of s-block which form ionic compounds to p-block elements which from largely covalent compounds. In this there are four periods in that one is incomplete, and eight groups are present. They are IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB in this VIII group three column are present. Note that elements of IIBgroup (Zn, Cd, and Hg) have a completely filled (n— 1)d Sub shell in their elementary form as well as in the combined state. Elements of the group IIIA (Sc, Y, La and Ac) and IIB (Zn, Cd, and Hg) are differ markedly in their properties from that of other transition elements. Hence, they referred to as non-typical transition elements while the other transition elements are called typical transition elements. Elements like Zn, Cd and Hg of the IIB group of the d block have completely filled the d-orbital and hence are not considered as transition elements. Non-typical transition elements are trivalent, diamagnetic and colourless while the typical transition elements show variable oxidation states, forms coloured ions and are paramagnetic. The d-block elements consist of three complete series each of 10 elements, involving the filling of 3d, 4d, 5d sub shells. They are named as 3d series or first transition series Scandium (21) to zinc (30), in which 3d orbital starts filling. 4d series or second transition series Yttrium (39) to Cadmium (48), in which 4d orbital starts filling. 5d series or third transition series lanthanum (57) Hafnium (72) to Mercury (80) in which 5d orbital starts filling. In addition to the complete three series there is a fourth incomplete row consisting of only three elements, (Rutherfordium by Americans) (104), Neilsbohrium (Ns) (Dubnum (Db) (105) Hassium (108) called 6d series. The transition elements or metals exhibit typical characteristic properties. Some of which are listed below Actinium (89), Kurchatorium Dr. Ramesh Yellapragada Lecturer in Chemistry A.B.N & P.R.R College of Science Kovvur

2. 2 1.Atomic and ionic radius 2. Electronic configuration 3. Variable oxidation states 4. Magnetic properties 5. Color 6. Complexes forming ability 7. Ionization energy 8. Catalytic properties 9. Metallic character and alloy forming ability. 10. Standard electrode potentials. 11. Reactivity. Atomic and ionic radii Generally atomic radii of the d-block elements of a given series decreases with increases of atomic number. However, the decrease across a period is not uniform. Due to the increase in the atomic number the nuclear charge increases which in turn increasingly tends to attract the electron cloud inward resulting in decrease in size, Note that the radii of the elements from chromium to copper are very close to one another because of screening effect, in the d-block elements the addition of electrons takes place in an inner (n—1)d sub shell which thereby adds to the primary screening effect. The additional electrons from the inward pull of the nucleus. As a result the size of the atom does not alter much in moving from Cr to Cu. In a given series the atomic radius decreases to a minimum for the group VIII elements and then increases again towards the end of the series. This is due to the repulsion among the added electrons. Atomic radius increases on descending the group. Exactly same values of atomic and ionic radii of second transition elements with the corresponding third transition series elements Zr & Hf , Nb & Ta, etc is due to a consequence of the filling of the 4f sub shell i.e. lanthanide contraction, poor shielding by intervening 4f electrons and greater nuclear charge in third transition elements. The ionic radii follow the same trend as the atomic radii. Atomic radii in A0 of the three series of Transition elements. Transition series I Sc1.62 A0 Ti 1.47 A0 V 1.34 A0 Cr 1.27 A0 II Y 1.80 A0 Zr1.60 A0 Nb1.46A0 Mo1.39 A0 III La1.87 A0 Hf1.58 A0 Ta1.46 A0 W 1.39 A0 IIIB IVB VB VIB VIIB Mn 1.26A0 Tc 1.36 A0 Re 1.37 A0 Dr. Ramesh Yellapragada Lecturer in Chemistry A.B.N & P.R.R College of Science Kovvur

3. 3 Electronic configuration: The general outer most electronic configuration of these elements is ns2 (n—1) d1—10. The electrons are filled in the orbital according normal Aufbau principle, Hund’s rule and Pauli’s exclusion principle. According to Aufbau principle the highest orbital 3d is filled after filling 4s in first transition series. Similarly in second and third series 4d is filled after 5s and 5d is filled after 6s respectively. 6d series is incomplete series is also filled after 7s. Scandium (21) to zinc (30) 4s2 3d1-10 First transition series/ 3d series Yttrium (39) to Cadmium (48) 5s2 4d1-10 Second transition series/ 4dseries Lanthanum (57) to Mercury (80) 6s2 5d1-10 Third transition series/ 5d series The exactly half filled and completely filled d- orbitals are more stable. This explains the anomalous electronic configuration of Chromium and copper because of the extra stability of the exactly half filled and completely filled d-orbitals.  In the similar way molybdenum (42) and silver (47) where the exactly half filled and completely filled orbitals give more stability. Chromium (24) 1s2 2s2 2p6 3s2 3p64s23d4 or 1s2 2s2 2p6 3s2 3p64s13d5 Molybdenum (42) 1s2 2s2 2p6 3s2 3p63d10 4s2 4p65s24d4 Or 1s2 2s2 2p6 3s23p63d10 4s2 4p65s15d5 Or Or Copper (29) 1s2 2s2 2p6 3s2 3p64s23d9 or 1s2 2s2 2p6 3s2 3p64s13d10 Or Variable oxidation states The tendency of an atom to lose or gain an electron is generally indicated by the oxidation state or states. Dr. Ramesh Yellapragada Lecturer in Chemistry A.B.N & P.R.R College of Science Kovvur

4. 4  It is always in combined form. It is either positive or negative. It is defined as the possible electronic charge which the atom of the element appears to have acquired in the given chemical form of the element in the compound. Variable oxidation state is one of the most striking features of the transition elements.  All transition elements except IIIB and IIB elements of each series exhibit variable oxidation states.  It is due to the fact that there is only a small difference between the energies of electrons in the ns electrons can be used for compound formation. Thus the variable oxidation states of transition elements are related to their electronic configurations.  In the First transition series the oxidation states are as followes Sc Ti V Cr Mn +2 +3 +3 +4 +4 +5 +5 +6 +6 +7 Fe +2 +3 (+4) +5 Co +2 +3 (+4) Ni +2 +3 +4 Cu +1 +2 Zn +2 +2 +2 +3 +2 +3 (+4) +2 (+3) +4 +5 In the first five elements of the first series up to Manganese in which 3d sub shell has only unpaired electrons, the minimum oxidation state is given by the number of electrons in the outer 4s-orbital (+2) and the maximum oxidation state is given by the sum of 4s and 3d orbital. In the next five elements in which 3d sub shell has some paired electrons, the minimum oxidation state is still the number of the outer 4s- electrons (+2) while the maximum oxidation state is not related at all with the electronic configuration, in fact it is rarely higher than +2 or +3. The +2 state becomes more stable, while +3 states become less stable across the period i.e. from left to right. Very high oxidation states cannot exist as the free ions, although oxy ions do exist. The maximum oxidation state in the first, second and third series are exhibited in KMnO4 Mn is +7, RuO4 & OsO4, Ru & Os in +8. Second and third transition series oxidation states: Y Zr Nb +2 +3 +3 +4 +4 +5 Mo +2 +3 (+4) +5 +6 Tc +2 +4 +7 Ru +2 +3 (+4) +5 +6 +7 +8 Rh +2 +3 (+4) +6 Pd +2 +3 +4 Ag +1 +2 Cd +2 +2 +2 +3 Dr. Ramesh Yellapragada Lecturer in Chemistry A.B.N & P.R.R College of Science Kovvur

5. 5 Hg +1 +2 La +2 +3 Hf +2 +3 +4 Ta +2 +3 +4 +5 W +2 +3 (+4) +5 +6 Re +2 +4 +7 Os +2 +3 (+4) +5 +6 +7 +8 Ir +2 +3 +4 Pt +2 +3 +4 +5 +6 Au +1 +2 Minimum oxidation states: All the transition elements with the expectation of Cr Cu, Ag, AU and Hg which have a minimum oxidation state of +1 exhibit a minimum oxidation state of +2. In most cases +2 oxidation state arises due to lose of two s electrons. Maximum oxidation states: Each of the elements in groups IIIB&VIIB can show the maximum oxidation state equal to its group number. Thus, Cr in a group VIB shows a maximum oxidation state +6 in K2Cr2O7. Most of the elements in VIII group show a maximum oxidation state equal to +6, however Ru & Os have a maximum oxidation state equal to +8, which is the highest oxidation state shown by any element. Relative stabilities of various oxidation states of 3d series elements can be correlated with the extra stability of 3d0 3d5&3d10configurations to some extent. Thus Ti+4(3d0) is more stable than Ti+3(3d1) similarly Mn+2(3d5) is more stable than Mn+4(3d4). Osmium (Os) and Ruthenium (Ru) belong to iron (Fe) group, but iron exhibits only +2or +3 but Os & Ru exhibits highest oxidation states. This is due to the higher oxidation states of 4d & 5d series elements are generally more stable than those of the elements of 3d series. The lower oxidation states particularly +2 and +3 are important in the chemistry of aquated and complex ions of 3d series elements, but these ions are not every important in the chemistry of 4d & 5d series. In short it may be said that in going down a sub-group a stability of the higher oxidation states increases while that of lower oxidation states decreases. IONISATION POTENTIAL The ionization potential of transition elements is fairly high due to their small size. The first I.P of transition elements lies between the values of those of s and p block elements. The first I.P of all transition elements lies between 5-10 eV. Dr. Ramesh Yellapragada Lecturer in Chemistry A.B.N & P.R.R College of Science Kovvur

6. 6 In transition elements the electron enters into the (n—1) d orbit which creates a shielding effect on the outermost ns electrons from the inward pull of positive nucleolus on the outer ns electrons. Thus, the effects of the increasing nuclear charge & the shielding effect created due to the expansion of (n—1) d orbital oppose each other. On account of this counter affects the I.P increase rather slowly moving in a period of the first transition series. First ionization potential of the first four elements Sc, Ti, V, and Cr have been almost close to one other. Similarly, the values of Fe, Co, Ni, and Cu also are fairly close one other. Second ionization potential is seemed to increase more or less regularly with the increase of atomic number. The value of I.P2 for chromium and copper are higher than those of their neighbors, due to the electronic configuration Cr+, Cu+ ions have extra stable 3d5 and 3d10 levels. If we move from IIB group (Zn, Cd, Hg) to IIIA group elements in p-block a sudden fall in the I.P is due to in IIIA the electron is removed from 4p orbital which is well shielded by the electrons in the inner shells and is incompletely filled. Where as in the IIB group elements the electron to be removed in 4s orbital which is completely filled, near to nucleolus and shielded by the nucleus than 4p orbital. The first I.P of transition elements lies between the values of those of s and p block elements. Hence these are less electropositive than the elements of IA & IIA elements. Hence the d-block elements will show a tendency to form covalent compounds under some conditions but fails to form ionic compounds so readily as the alkali and alkaline earth metals. Generally, these elements form ionic compounds in lower oxidation states whereas in higher oxidation states form covalent compounds. Metallic character: All the transition elements are metals, since the number of electrons in the outer-most shell is very small, i.e. two. They are hard malleable and ductile. They exhibit all the three types of face centered cubic (fcc), hexagonal close packed (hcp) and body centered cubic (bcc) structures. Both covalent and metallic bonds exist in the atoms of transition metals. The presence of d-orbitals favors covalent bonding. These metals are good conductors of heat and electricity.  How ever they differ from non- transition metals in being hard and brittle but exceptional behavior is associated with mercury which is liquid and quite soft like alkali metals.  The VIII and IB group metals are soft and more ductile. Dr. Ramesh Yellapragada Lecturer in Chemistry A.B.N & P.R.R College of Science Kovvur

7. Alloy Formation An intimate mixture having physical properties similar to that of the metal, formed by a metal with other metals or metalloids or sometimes a non-metal, is called as an alloy. Which are also called solid solutions. Generally pure metals have poor mechanical properties. Therefore, they are not used as such in industry. Alloys are prepared to modify the properties of metals, like malleability, ductility, toughness, resistance to corrosion, etc. So as to suit in industry and in domestic life of men. Transition metals play a vital role in forming alloys Examples Ornament Gold is an alloy of Au and Cu Brass 60-80% Cu and 20-40% Zn used in machinery parts Bronze: 75-90% Cu and 10-25%tin Sn used in coins and statues making. Germen silver 50-60% Cu, 10-30% Ni and 20-30% Zn used in spoons forks. Inver, Nichrome, Duralumin, Aluminum Bronze, Bell metal etc are also alloys. Colour & Spectral Behavior Many ionic and covalent compounds of transition elements are colored in their solid or in solution state. This is in contrast of the compounds of s-and p-block elements which are almost always white. When light passes through a material some light radiations might be absorbed by the substance, if the absorption occurs in the visible region of the spectrum, the transmitted light is colored with the complimentary color of the absorbed color of light. Absorption in the visible and UV region of the spectrum, is caused by change in electronic energy, however if the energy jumps are large so that the absorption lies in the uv region as in s-and p-block elements, all the visible radiations will be emitted. Hence their compounds are appeared as white. In case of d-block elements the energy jumps are small so that the absorption lies in the visible region and hence their compounds appear in the complimentary color of the absorbed color. Hydrated Cu+2ion absorbs radiations corresponding to red light and hence it transmits radiations of wavelength corresponding to blue color which is complementary to red color. The color of the transition metal ion is associated with (i) An incomplete d-level between 1 and 9 d electrons (ii) The nature of the ligands surrounding the ions Absorption in the visible and UV regions of the electromagnetic radiations cause’s energy changes in the electrons. Therefore the spectrum is also known as electronic spectrum. The color of the transition metal ions depends on the number of unpaired electrons in its d-orbitals. 7 Dr. Ramesh Yellapragada Lecturer in Chemistry A.B.N & P.R.R College of Science Kovvur

8. 8 The d-orbitals of a free isolated and gaseous transition metal ion have equal energies. i.e. they are degenerate orbitals but the d-orbitals of metal or metal ion in its compounds or hydrated ions or complexes differ though slightly, in their energies. This is due to the splitting of d orbitals into two sets of different energies. One set is (dx—y), (dz) are called eg orbitals and the other set is dxy, dyz, dzx are called t2gorbitals this is due to their symmetry. It is called d-orbital splitting. The energy of these orbitals depends on the direction of ligands. In octahedral complexes t2g orbitals are at lower energy than Eg orbitals, the electrons in the lower level can be excited to higher level by absorbing energy this is called d-d transitions or excitation.  Less amount of energy is required for this excitation. It takes place under the influence of the anions of the compound or of water molecules bound to the metal ion in the hydrated ion. The absorption of visible light and hence colored natured of the transition metal cations is due to the promotion of one or more un paired d- electrons from a lower to higher level within the same d-sub shell. This promotion requires small amount of energy. The absorption spectra of transition metal ions show that visible and UV light is absorbed, the bands of visible spectrum have low intensity or low molar extinction coefficient. The absorption bands are due to electronic transitions within the same d- orbitals called d-d transitions. The absorptions bands in the UV region have high extinction coefficients. In UV absorption spectra are produced due to charge transfer from ligands to the metal ion. Such spectra are known as charge transfer spectra. Cr+6, Mn+7 forms oxo anions like Cr2O7—2, CrO4—2 and MnO4— etc., are strongly colored ions these are not due to d-d transitions but are due to charge transfer spectra. Some typical transition metal cations like Cu+, Ag+, Ti+4, Sc+3, Hg+2 Zn+2 Cd+2 etc are colorless because they have either completely empty or fully filled d- orbitals, i.e. they do not have any unpaired d-electrons and hence appear colorless. Dr. Ramesh Yellapragada Lecturer in Chemistry A.B.N & P.R.R College of Science Kovvur

9. 9 Name of the ions Sc+3, Cu+, Zn+2 Ti+3 Cu+2 V+3, Fe+2, Ni+2 Cr+3, Mn+3 Mn+2, Co+2 Fe+3 3d electron Configuration 3d0, 3d10, 3d10 3d1 3d9 3d2, 3d6, 3d8 3d3, 3d4 3d5, 3d7 3d5 Number of unpaired electrons Zero One One two, four, two Three, Four Five, Three Five Colour Colorless Purple Blue Green Violet Pink Yellow Color absorbed Approx. wavelength Absorbed color in nm 400-450 450-490 480-490 490-500 500-560 560-575 575-590 590-625 625-750 Complementary color of the absorbed color Yellow-green Yellow Orange Red Purple Violet Blue Green blue Blue-Green Violet Blue Green Blue Blue Green Green Yellow Green Yellow Orange Red 10A0= I mμ = I nm Complex forming ability: The transition metal cations have a great tendency to form complexes with several molecules or ions called ligands. Ligands are molecules or ions with lone pair(s) of electrons which they can donate very easily to central metal ion. These are neutral or negatively charged ions. CN—, Cl—, CO, NH3 etc. The tendency of formation of complexes is due to following factors (i) The cations are relatively very small in size and have high effective nuclear charge. Thus they have a high positive charge density which facilitates the acceptance of lone pairs of electrons from other molecules or ions. (ii) The transition metal cations have vacant inner (n—1)d-orbitals which are of appropriate energy to accept lone pair of electrons from the ligands. (iii) The bonds involved in the formation of complexes are co ordinate covalent bonds; hence the complexes are termed as co-ordinate complexes. (iv) The structure commonly found in such complex ions is linear, square planar, tetrahedral and octahedral depending upon the nature of the hybridization of the metal ion orbitals, i.e. CN- 2, CN- 4, and CN- 6 respectively. (v) The transition metals are capable of showing several oxidation states. Dr. Ramesh Yellapragada Lecturer in Chemistry A.B.N & P.R.R College of Science Kovvur

10. 10 Examples: K4 [Fe (CN6)] [Co (NH3)6] Cl3 etc. According to Pearson’s concept of Hard and Soft Acids and Bases metal ions are regarded as hard or soft acids and the ligands are hard or soft bases. Hard acid may combine with a hard base and a soft acid can combine with a soft base to form complex. In each transition series the stability of complexes increases with increasing atomic number of the element and in a particular oxidation state with decreasing size of its atoms. When the transient metal atom exhibits more than one oxidation state, the higher valent ion forms more stable complexes.  In the complex compounds metal ions have two types of valences they are primary valency or oxidation number and secondary valency or coordination number. Secondary valency or coordination number is noting but the number of ligands attached to the central metal atom or ion. Magnetic properties: Substances are classified into following three types based on the magnetism. Para magnetic substances: When a substance is place in a strong magnetic field H(gauss), if the magnetic lines of force are drawn into the substance, the field (B) in the substance is greater than the applied field (H) i.e. B>H. such substance is called as paramagnetic substance, which are weakly attracted into the magnetic field. These substances lose their magnetism on removing the magnetic field. Para magnetism is caused by the presence of unpaired electrons and since most of the transition metal atoms have unpaired d-electrons are paramagnetic in nature. Diamagnetic substances If the magnetic lines of force are repelled by the substance, B<H then the substance is called diamagnetic substance which are repelled by magnetic field. It is the property of the completely filled electronic sub shells. Compared to diamagnetic effect, paramagnetic effect is more pronounced and the magnetic moments in paramagnetic substances increase with the number of unpaired electrons. The magnetic property generally expressed in Bohr magnetons (μBM) The magnetic moment of any substance arises from the spin of the electrons i.e. unpaired electrons and orbital motions of electrons. Dr. Ramesh Yellapragada Lecturer in Chemistry A.B.N & P.R.R College of Science Kovvur

11. 11 The total magnetic moment of a cat ion depends upon the number of unpaired electrons and is given by the following expression. μ = square root of n(n+2) Where n is the number of unpaired electrons Those substances which do not lose their magnetism, on removing the magnetic field are called ferromagnetic. These substances are strongly attracted by the magnetic field.  Fe, Co, Ni ete have unpaired electron spins are much more paramagnetic then the other elements. Hence these are said to be ferromagnetic. Sc+3, Zn+2, Cd+2, Hg+2, Ti+4, Cu+, Ag+ etc have no unpaired electrons hence these are diamagnetic. K3 [Fe (CN6)], Cu+2, Cr+2, etc are paramagnetic. Catalytic properties Transition metals and many of its compounds form important catalysts in industry and in biological systems. This property may be either due to their variable valency incomplete-d- orbitals and variable oxidation states, which enables them to form unstable intermediate compounds or due to providing a suitable reaction surface. Example: 1. In contact process for the manufacture of H2SO4-either V2O5 or a vanadate is used as a catalyst to oxidize SO2 to SO3. 2. Polymerization of ethylene using titanium IV chloride catalyst. 3. Iron and Mo are used in the preparation of NH3in Heber’s process. 4. Raney Nickel is used in hydrogenation reactions and in Desulpharification in the organic reactions. 5. K4 [Fe (CN6)] is used in the qualitative analysis to identify the cations like Cu+2, Fe+2, Fe+3, Zn+2, Ca+2 etc type cations. 6. Fenton’s reagent FeSO4/H2O2 is used in the oxidation of primary alcohols to aldehydes etc. 7. MnO2 acts as a catalyst in the decomposition of KClO3. 8. Nickel / platinum/palladium is used in the hydrogenation of oils. MELTING AND BOILING POINTS AND DENSITIES The melting and boiling points of the transition elements are generally high. This is due to (i) strong metallic bonding because of the overlapping of (n—1)d orbitals (ii) Covalent bonding of unpaired d-orbital electrons. Bohr Magnetons Dr. Ramesh Yellapragada Lecturer in Chemistry A.B.N & P.R.R College of Science Kovvur

12. 12 Zn, Cd, Hg have completely filled (n—1) d orbitals, their atoms are not expected to form covalent bonds hence they have relatively low m.p than other d-block elements. The melting and boiling points do not show any definite trend in the three transition series. As result the decrees in the atomic volume the density of these elements increases, consequently transition elements have high densities. In a given transition series the density increases across the period and reaches a maximum value at group VIII. In moving down the group the density increases. Since the atomic size of the transition series second and third is same but atomic weights increases Reactivity The reactivity of d-block elements is less due to the following factors. a)The transition elements have high ionization energies b)The transition metal ions do not get hydrated easily and so have less heat of salvation or low heat of hydration. c)The M.P & B.P of transition elements are very high, indicates high heat of sublimation. Standard electrode potentials The potential of any electrode commonly known as single electrode potential, it is the potential difference between it and the electrolyte surrounding the electrode. The electrode potential depends upon the nature of the metal, concentration if the metallic ions in solution and the temperature of the solution. When the ions are at unit activity and the temperature is 250c the potential difference is called as standard electrode potential E0. The values of standard oxidation potentials of transition elements except Cu and Hg is lower than that of hydrogen, thus all the elements except Cu and Hg would evolve H2 gas from acid solutions according to the equation. M + 2H+from acid A Latimer diagram is a graph that summarizes the standard electrode potentials of an element in different oxidation states. It's a compact way to show an element's redox chemistry. A Latimer diagram for the 3d series of d-block elements (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) is a compact way to represent the standard reduction potentials of these elements in various oxidation states, typically in acidic conditions, helping to predict the stability of different oxidation states and redox reactions For Manganese (Mn), the Latimer diagram in acidic conditions would show the following (simplified): M+2 + H2gas Dr. Ramesh Yellapragada Lecturer in Chemistry A.B.N & P.R.R College of Science Kovvur

13. 13 MnO4- (7+) -> MnO2 (4+) -> Mn2+ (2+) -> Mn (0) E° (V) -> 1.51 -> 1.23 -> -0.95 Latimer diagrams are useful for comparing the redox chemistry of different elements under similar conditions. For instance, the redox behavior of mercury and its congeners in acid solution may be easily compared using the Latimer diagrams. How it works The most oxidized form of the element is on the left, and the most reduced form is on the right. The standard reduction potential is written above the reaction arrow. The diagram is usually created for standard conditions, such as in strong acid or strong base. The diagram can help you disproportionate. Uses Latimer diagrams are useful for comparing the redox properties of elements. They can also help you determine if a substance is stable to disproportionation. Latimer diagrams can be used to summarize a large amount of information in a compact form. The reduction potential depends on the pH of the solution. Latimer diagrams are also known as reduction potential diagrams. Latimer diagrams are the oldest and most compact way to represent electrochemical equilibria. predict whether a metal will Dr. Ramesh Yellapragada Lecturer in Chemistry A.B.N & P.R.R College of Science Kovvur

14. 14 Dr. Ramesh Yellapragada Lecturer in Chemistry A.B.N & P.R.R College of Science Kovvur