Transition Metals. Thursday 09/10/15. Thursday, September 10, 15

Transcription

1 Transition Metals Thursday 09/10/15

2 Agenda Review assigning oxidation numbers and practice with partners Start topic 13.1 First row d-block elements - Transition Metals

3 Rules for assigning oxidation numbers

4 Rules for assigning oxidation numbers Rule 1: The oxidation number of an element in its free (uncombined) state is zero (i.e. Al (s) or Zn (s) ). This is also true for elements found in nature as diatomic (two-atom) elements (i.e. H 2, F 2, O 2 ) and for sulfur which is S 8. Rule 2: The oxidation number of a monatomic (one-atom) ion is the same as the charge on the ion (i.e. Na + = 1+, S 2- = 2-) Rule 3: The sum of all oxidation numbers in a neutral compound is zero. The sum of all oxidation numbers in a polyatomic (manyatom) ion is equal to the charge on the ion. This rule often allows chemists to calculate the oxidation number of an atom that may have multiple oxidation states, if the other atoms in the ion have known oxidation numbers. (i.e. NaOH = 0 SO 4 2- = 2-) Rule 4: The oxidation number of an alkali metal (IA family) in a compound is +1; the oxidation number of an alkaline earth metal (IIA family) in a compound is +2.

5 Rules for assigning oxidation numbers Rule 5: The oxidation number of oxygen in a compound is usually 2. If, however, the oxygen is in a class of compounds called peroxides (for example, hydrogen peroxide), then the oxygen has an oxidation number of 1. If the oxygen is bonded to fluorine, the number is +1. Rule 6: The oxidation state of hydrogen in a compound is usually +1. If the hydrogen is part of a binary metal hydride (compound of hydrogen and some metal), then the oxidation state of hydrogen is 1. Rule 7: The oxidation number of fluorine is always 1. Chlorine, bromine, and iodine usually have an oxidation number of 1, unless they re in combination with an oxygen or fluorine. You can say a substance has been oxidized when there is an increase in its oxidation number. You can also say a substance has been reduced when there is a decrease in the oxidation number.

6 OIL RIG Oxidation is the LOSS of electrons Zn (s) Zn e - (notice the increase in oxidation #) Reduction is the GAIN of electrons Cu e - Cu (s) (notice the decrease in oxidation #)

7 Assigning oxidation numbers practice You may work alone or with a partner You have about 40 minutes to finish the handout

8 The Periodic Table - The Transition Metals First-row d-block elements Colored complexes Ms. Thompson - HL Chemistry Wooster High School

9 Topic 13.1 First-row d-block elements Transition elements have variable oxidation states, form complex ions with ligands, have colored compounds, and display catalytic and magnetic properties. Zn is not considered to be a transition element as it does not form ions with incomplete d orbitals. Transition elements show an oxidation state of +2 when the s- electrons are removed.

10 Nature of science Looking for trends and discrepancies - transition elements follow certain patterns of behavior. The elements Zn, Cr, and Cu do not follow these patterns and are therefore considered anomalous in the first-row d-block.

11 First-row d-block elements Transition elements have an incomplete d-sublevel, and can form positive ions with an incomplete d-sublevel Found in first row in period 4 from scandium (Sc) to copper (Cu) The Lanthanoids are the elements from Z=57 to Z=71 and the actinoids are elements from Z=89 to Z=103. Lanthanum and Actinium are the only two elements in that period that do not contain an f-orbital. Other f-block elements are group 3 but they form a separate f-block in the periodic table. Group 12 elements (Zn, Cd, Hg, and Cn) are not classified as transition elements according to IUPAC as they all have full d- sublevels containing 10 electrons. Zn = [Ar]4s 2 3d 10

12 First-row d-block elements Anomolies with electron configurations: Cr & Mo [Ar]3d 4 4s 2 While most would say this is the configuration - it is NOT! As you recall, orbitals are MORE stable when they are half full, full, or empty... As you can see the d-orbital is partially full -- UNSTABLE! So what does the electron configuration really look like for Cr? [Ar]3d 5 4s 1 WHY!?

13 First-row d-block elements Anomolies with electron configurations: Cu & Ag [Ar]3d 9 4s 2 While most would say this is the configuration - it is NOT! For Cu and Ag - they prefer FILLED sublevels So what does the electron configuration really look like for Cu? [Ar]3d 10 4s 1 WHY!?

14 First-row d-block elements Though those explanations are far too simplistic and the true extent is beyond the scope of this course Must take into consideration the nuclear charge effect on the 4s and 3d orbitals and interactions of electrons within the same orbital A different energy must be considered, pairing energy, p, which arises from the electrostatic repulsion of like charges. As nuclear charge increases, there is greater attraction of the electrons: d orbitals are not shielded from nucleus to same extent as other orbitals. As a result electrons will occupy lowest available orbitals

15 Periodic table of elements Main-group elements group 1 (excluding H), group 2, and groups Transition elements groups 3-11 (the f-block elements are sometimes described as inner transition elements) s-block elements p-block elements d-block elements f-block elements Lanthanoids Actinoids groups 1and 2 and He groups (excluding He) groups 3-12 (including La and Ac), but excluding Ce to Lu and Th to Lr, which are classified as f-block elements elements Ce to Lu and from Th to Lr elements La to Lu elements Ac to Lr

16 Electron configuration of first-row d-block elements and their ions Know how to write full and condensed electron configurations for the first 36 elements (Z = Kr). When removing electrons to form cations (positive ions) electrons are always removed from the level of the highest principal quantum number, n. In the case of the first-row d-block elements this will be the 4s level.

17 Characteristics of transition elements L to R Periodic table: Nuclear charge (Z) increases and atomic radii decrease First ionization increases (IE) will increase across a period. For transition elements IE is much more gradual and rate of increase is much lower compared compared to main-group elements. Electrons of transition elements enter an inner shell instead of a valence shell orbital -- greater shielding effect Transition metals have numerous key characteristics: variable oxidation states compounds of transition elements and their ions are often coloured form complexes with ligands magnetic properties depend on their oxidation states and coordination number

18 Variable oxidation states Often have different oxidation states unlike alkali and alkaline metals Sc Ti V Cr Mn Fe Co Ni Cu Zn Type A: Sc, Ti, and V Type B: Cr and Mn Most common oxidation state Type C: Fe, Co, Ni, Cu, and Zn

19 Sc Ti V Characteristics of Type A stable high oxidation states i.e. V is +5 in VO3 - unstable low oxidation states Type A: Sc, Ti, and V

20 Cr Mn Type B: Cr and Mn Characteristics of Type B stable high oxidation states i.e. Mn is +7 in MnO4 -, Cr is +6 in Cr2O7 2- stable low oxidation states i.e. Mn is +2 in [Mn(H2O)6] 2+, Cr is +3 in [Cr(H2O)6] 3+

21 Fe Co Ni Cu Zn Characteristics of Type C unstable high oxidation states stable low oxidation states i.e. Fe is +2 in [Fe(H2O)6] Type C: Fe, Co, Ni, Cu, and Zn