1. 1Chemistry 2C Lecture 8: April 14 th, 2010 Lecture 8:Transition Metals I.Electronic Configuration II.Transition Metal properties III.Properties, Oxidation States IV.Magnetic Properties V. Chromium VI.Complexes and Coordination

2. 2Chemistry 2C Lecture 8: April 14 th, 2010 How are Ionization Energies, Standard Reduction Potentials, Gibb’s Energies and Activity Series related? But First a question…

3. 3Chemistry 2C Lecture 8: April 14 th, 2010 Transition Metals Facts Many of the most important metals in modern society are the transition metals In the periodic table, they comprise of more than half of the elements.

4. 4Chemistry 2C Lecture 8: April 14 th, 2010 Transition Metals Facts Where are they: The s block elements- Groups 1 & 2 (1A-2A) The p block elements- Groups 13-18 (3A-8A) The d block elements- Groups 3-12 (3B-1B) The f block elements

5. 5Chemistry 2C Lecture 8: April 14 th, 2010 Transition Metals Facts Electronic configurations for noble gases [He]1s 2 [Ne]1s 2 2s 2 2p 6 [Ar]1s 2 2s 2 2p 6 3s 2 3p 6 In multi-electron atoms (not Hydrogenic atoms), the orbital energies are like this (qualitative) 1s 2s 2p 3s 3p 4s 3d Energy 3d 4p Each box is an orbital (can hold 2 e-) Within each sub-shell, the orbitals are degenerate (same energy) The three p oribals are degenerate The five d-orbiatal are degenerate

6. 6Chemistry 2C Lecture 8: April 14 th, 2010 Transition Metals Facts n, l, m l, m s nPrinciple quantum number langular momentum QN m l magnetic QN m s spin QN Recall the Pauli exclusion principle: No two electrons in an atom can have the same set of four quantum numbers 3d For the 3d orbitals n=3 l=2 m l = -2, -1, 0, 1, 2 M s = ½ or -½ Orbitals can hold a max of 2 electrons and they must be of opposite spin: So there are 2x5 elements for each row of d-block Transition metals

7. 7Chemistry 2C Lecture 8: April 14 th, 2010 Electronic configuration After Ar, things get more interesting, complex, and even cool! Can simplify the electronic configuration by using the configuration of the closest noble gas configuration (e.g. Ar) [Ar]:1s 2 2s 2 2p 6 3s 2 3p 6 [K]:1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 [Ca]:1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 Now we start to fill in the d-orbitals [Sc]:1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 1 d-oribitals [Sc]:[Ar] 4s 2 3d 1

8. 8Chemistry 2C Lecture 8: April 14 th, 2010 Electronic configuration Orbitals are filled according to Hund’s rule – unpaired electrons first before putting two electrons in a single orbital [Mn]:[Ar] 4s 2 3d 5 ↑↓↑↑↑↑↑ 4s 3d All five d electrons are unpaired and occupy separate orbitals

9. 9Chemistry 2C Lecture 8: April 14 th, 2010 Electronic configuration Orbitals are filled according to Hund’s rule – unpaired electrons first before putting two electrons in a single orbital [Co]:[Ar] 4s 2 3d 7 ↑↓ ↑↑↑ 4s 3d Now two d-oribtals are occupied with two electrons (m s = ½ and m s = -½)

10. 10Chemistry 2C Lecture 8: April 14 th, 2010 Electronic configuration After the d orbitals are filled, the 4p orbitsal will start to be filled starting with Ga and continuing until Kr [Kr]:[Ar] 4s 2 3d 10 4p 6 ↑↓ 4s3d The same pattern occurs in the next row, so that the 5s is filled before 4d, which is then filled before 5p ↑↓ 4p

11. 11Chemistry 2C Lecture 8: April 14 th, 2010 Rare Earth Transition Metals After the 6s, there is a break and the then start to fill the 4f orbitals Lanthanide Elements Actinide Elements

12. 12Chemistry 2C Lecture 8: April 14 th, 2010 Rare Earth Transition Metals The 4f and the 5d energies are close, so there is some mixing with the d-block metals, but mostly the order is: 6s, 4f, 5d, 6p [La]: [Xe] 6s 2 5d 1 [Ce]: [Xe] 6s 2 4f 1 5d 1 Table D in the text book (pg. A17) The first two lanthanides Actinides: Rare and radioactive and will be discussed later

13. 13Chemistry 2C Lecture 8: April 14 th, 2010 Transition Metals So, the transition elements” term refers to the d-block and also the f-block elements. The name also refers to their intermediate properties between the very reactive s-block and less reactive p-block metals

14. 14Chemistry 2C Lecture 8: April 14 th, 2010 Transition Metals Properties Transition metals are all metals which means: 1)Clean metallic surface has a characteristic luster 2)Conduct heat well (flow of thermal energy) 3)Conduct electricity (flow of electrons) 4)Most are malleable (can be hammered) 5)Most are ductile (can be drawn in a wire Most TS have high melting points except Zn, Cd, Hg (weaker metallic bonding) e.g. V, 1917 ◦ C e.g. Zn, 420◦C Atomic radius (result from the combination of several factors) 1)As nuclear charge ↑ and electrons ↑, the effective nuclear charge exerts a greater pull on the valence electrons and they are pulled in close; thus atomic radii decrease in going from Left to Right in a row 2)However, electrons in the d-subshell tend to experience repulsive effects and expand the radius

15. 15Chemistry 2C Lecture 8: April 14 th, 2010 Main Group Atomic Radii

16. 16Chemistry 2C Lecture 8: April 14 th, 2010 Transition Metals Radii 21 [Sc][Ar] 4s 2 3d 1 161 pm 22 [Ti][Ar] 4s 2 3d 2 145 pm 23 [V][Ar] 4s 2 3d 3 132 pm 24 [Cr][Ar] 4s 1 3d 5 125 pm 25 [Mn][Ar] 4s 2 3d 5 124 pm 26 [Fe][Ar] 4s 2 3d 6 124 pm 27 [Co][Ar] 4s 2 3d 7 125 pm 28 [Ni][Ar] 4s 2 3d 8 125 pm 29 [Cu][Ar] 4s 1 3d 10 128 pm 30 [Zn][Ar] 4s 2 3d 10 133 pm Z (nuclear charge)MetalsElectronic ConfigurationMetallic Radius 100 pm=1Å Special stability of half filled shells results in extra energy required to pair electrons

17. 17Chemistry 2C Lecture 8: April 14 th, 2010 Transition Metal Radii

18. 18Chemistry 2C Lecture 8: April 14 th, 2010 Lanthanide Contraction Z (atomic number) Metallic radius Sc Zn Y Cd La Hg Reason: Between the 2 nd and 4rd series, the 4f subshell is filled and these f electrons do a poor job of shielding the nuclear charge due to their radial distance function (Quantum Mechanical result)

19. 19Chemistry 2C Lecture 8: April 14 th, 2010 Oxidation States Sc metal[Ar] 4s 2 3d 1 Sc 2+ [Ar] 3d 1 Sc 3+ [Ar] (most stable and hence most common) Ti metal [Ar] 4s 2 3d 2 Ti 2+ [Ar]3d 2 Ti 3+ [Ar]3d 1 Ti 4+ [Ar] (most stable and hence most common) 1. All transition metals have +2 oxidation states corresponding to the loss of the two s electrons. These are lost first! Note, the max oxidation state corresponds to the group number!

20. 20Chemistry 2C Lecture 8: April 14 th, 2010 Oxidation States 22Ti 2+ [Ar]3d 2 Also the +2 ions have the # of d electrons given in the own column of atomic number Useful device…. 21Sc 2+ [Ar]3d 1 26Fe 2+ [Ar]3d 6 … … 30Zn 2+ [Ar]3d 10

21. 21Chemistry 2C Lecture 8: April 14 th, 2010 Oxidation States Stability of the oxidation state depends highly on the nature of the element. Common ox. states in red V+1, +2, +3, +4, +5 Cr+1, +2, +3, +4, +6 Mn+1, +2, +3, +4, +6, +7 Element Oxidation State Fe+2, +3 Co+2, +3 Ni+2 Cu+1, +2 Zn+2 As I.E. increases, the harder it is to remove multiple d electrons

22. 22Chemistry 2C Lecture 8: April 14 th, 2010 Oxidation States All the highest oxidation states are found in combination with F, the most electronegative element and usually also w/ O e.g. CrF 6 chromium (VI) hexafluoride +6 CrO 4 2- -2 chromate ion +6

23. 23Chemistry 2C Lecture 8: April 14 th, 2010 Bonding, Colors and Magnetism All of these properties depend on the participation of the d- or f- electrons in the transition metal elements. However, d-electrons do not play a role in the bonding of main group elements to any reasonable degree. Magnetism: Most materials we encounter have no obvious magnetic properties - they are said to be non-magnetic. In these materials, the magnetic fields of the individual atoms are randomly aligned and thus tend to cancel out:

24. 24Chemistry 2C Lecture 8: April 14 th, 2010 Bonding, Colors and Magnetism All of these properties depend on the participation of the d- or f- electrons in the transition metal elements. However, d-electrons do not play a role in the bonding of main group elements to any reasonable degree. Magnetism: When most people talk about magnets, they are referring to “ferromagnets,” which have permanent (or long-living) magnetic properties (e.g. Fe, Co, and Ni).

25. 25Chemistry 2C Lecture 8: April 14 th, 2010 Ferromagnets These have domains in which the magnetic fields of the individual atoms align, but the orientation of the magnetic fields of the domains is random, giving rise to no net magnetic field. But when an external magnetic field is applied to them, the magnetic fields of the individual domains tend to line up in the direction of this external field, due to the nature of the magnetic forces, which causes the external magnetic field to be enhanced.

26. 26Chemistry 2C Lecture 8: April 14 th, 2010 Paramagnetic vs. Diamagnetic Paramagnetic materials are attracted when subjected to an applied magnetic field. Electrons not only go around the atom in their orbitals, they also spin, which creates a magnetic field. Unpaired electrons spin in the same direction as each other, which increases the magnetic field effect. When the electron in an orbital become paired with another electron in that orbital, the new electron spins in the opposite direction and this cancels the effect of the first electron. Oxygen is a paramagnet because the electronic structure for the diatomic has unpaired electrons (molecular orbital theory)

27. 27Chemistry 2C Lecture 8: April 14 th, 2010 Paramagnetic vs. Diamagnetic Diamagnets are repelled by magnetic fields. However, since diamagnetism is such a weak property its effects are not observable in every-day life and simply no effect is observed. Levitate Graphite.Levitate a live frog

28. 28Chemistry 2C Lecture 8: April 14 th, 2010 Let’s focus on Chromium Main ore: Fe(CrO 2 ) 2 “chromite” Chromium exhibits a large range of colors, so names from “chroma”, Greek for color +3+2 Fe/Cr alloy: “ferrochrome” and is used in stainless steel Reduction Oxidation, O 2 and Na 2 CO 3 Na 2 CrO 4 : Sodium chromate and is yellow in solution In acid solution, the color turns to orange 2CrO 4 2- + 2H+ Cr 2 O 7 2- + H 2 0 This is NOT a redox reaction! +6

29. 29Chemistry 2C Lecture 8: April 14 th, 2010 Let’s focus on Chromium 2CrO 4 2- + 2H+ Cr 2 O 7 2- + H 2 0 Cr O O O O 2- Cr O O O 2- Cr O O O In basic solution CrO 4- is favored. The dichromate ion is used in the tanning of leather Cr 2 O 3 (chromium (III) oxide) is an abrasive and is used in sand paper as a green pigment When mixed with Al 2 O 3, gives a red color or rubies and when in glass gives an orange color

30. 30Chemistry 2C Lecture 8: April 14 th, 2010 Complexes/Coordination compounds When discussing electrochemistry, we took care to write species like Fe 2+ (aq) and Cu + (aq). Why? Because transition metal cations don’t like to be “bare.” In aqueous solutions, there will be a strong electrostatic attraction between the metal cation and the solvent water molecules (solvation) Fe 2+ O H H ++ -- Negative end of water dipole due to electronegativity of O > H When an optimal distance is reached, a chemical bond is formed between the Fe and the O using the lon pair of electrons on O

31. 31Chemistry 2C Lecture 8: April 14 th, 2010 Complexes/Coordination compounds In such a case, both electrons that form the covalent bond come from the ligand (water) and more specifically, the oxygen atom! Fe 2+ We often say that the lone pair is “donated to” the iron atom The metal-water bond is also called a “coordinate covalent bond” OH 2 Think of the metal as the electron acceptor And ligand as the electron donor Or metals are Lewis Acids And ligands are Lewis Bases

32. 32Chemistry 2C Lecture 8: April 14 th, 2010 Complexes/Coordination compounds Complexes are composed of a)a central metal atom or ion and b)surrounding ligands bound to the metal Several ligands coordinate to the metal and make up the “coordination sphere.” Typically, 2, 4 or 6 are observed, but all numbers up to 12 are possible. The coordination number for a metal atom/ion is determined a lot by the size and shape of the occupied orbitals and bonding considerations (e.g. the larger the metal the more ligands can bind to it).

33. 33Chemistry 2C Lecture 8: April 14 th, 2010 Complexes/Coordination compounds The number of ligands bound to the metal is called the coordination number. Pt NH 3 H3NH3N H3NH3N Cu OH 2 H2OH2O H2OH2O The Pt had a coordination number of 4 The Cu had a coordination number of 6. Also, the coordination sphere is make up of six water molecules Both of these species are called “complexes” The square brackets imply that this is a stable unit and that it tends to be preserved in both the solid and the solution phase. 2+

34. 34Chemistry 2C Lecture 8: April 14 th, 2010 Pop Quiz: The oxidation state of Co atom is __________ 1. Consider the compound [CoCl(NH 3 ) 5 ]Cl 2 The Coordination number of Co atom is __________ hexaaquamanganese (II) sulfate __________ 2. Write the structural formula for the following transition metal complex: tetraamminedibromozinc (II) sulfate __________

35. 35Chemistry 2C Lecture 8: April 14 th, 2010 Pop Quiz: 3. How many d electrons does copper (I) have?_____