1. Recap – Last Lecture 1

2. Follow on from last lecture 2 Note Cr and Cu have ‘unexpected’ electron configurations; understandable in terms of additional stability of half-filled or completely-filled sub-shells. Cr expect: [Ar] 4s 2 3d 4 ; observe [Ar] 4s 1 3d 5 Cu expect:[Ar] 4s 2 3d 9 ; observe [Ar] 4s 1 3d 10

3. 3 Periodic Trends The chemistry of an element is directly related to its valence electron configuration. Many physical properties result from the attraction of the valence electrons to the nucleus of the atom. Attraction of e - to nucleus Atomic No

4. 4 Ionisation energy X(g) X + (g) + e - Increases across a period; decreases down a group.

5. 5 Ionisation energy X(g) X + (g) + e - Trend reflects effective nuclear charge.

6. 6 Atomic Radius The atomic radius decreases across a period and increases down a group. Again, trend reflects effective nuclear charge.

7. 7 Atomic Radius Cation neutral atom.

8. 8 Electronegativity Electronegativity is an empirical scale that represents the ability of an atom, when in a compound, to attract the electrons of a chemical bond towards itself.

9. 9 d-block elements Trends are observed but are not as clear as the trends in the s- and p- blocks.

10. 10 d-block elements 4d and 5d elements have very similar sizes due to the ‘lanthanide contraction’. Elements in the same Group of the 4 th and 5 th period are almost always found together in minerals and ores.

11. 11 Elements and the body Percentage of atoms in a human: In a 75 kg adult, typical mass of metals:

12. 12 Elements and the body essential toxic archaeamedicinal

13. 13 Elements and the body Group 1 & 2 ions present in relative high concentrations. Many roles, for example: –Na + maintains osmotic balance (correct hydration) –K + in glucose metabolism & protein synthesis –Mg 2+ involved in transport & hydrolysis of ATP –Ca 2+ is the cation in structural biominerals (teeth, bones)

14. 14 Elements and the body Many transition metals have a wide range of oxidation states and form stable complexes. Consequently they are often found at the active site of enzymes, for example: –Fe 2+ oxygen transport (hemoglobin) –Cu + /Cu 2+ electron transfer catalysts –Zn 2+ structural role in enzymes http://en.wikipedia.org/wiki/Zinc_finger

15. 15 Trace metals or toxic metals All elements are toxic if in high enough concentrations. Most biologically important elements have an optimum range in which they are beneficial. Toxic metals in any concentration are harmful.

16. 16 Applications http://en.wikipedia.org/wiki/CYP17A1# /media/File:3ruk.png Cytochrome P450 is one example of an enzyme involved in electron transfer chains with a heme-iron center. About 75% of the metabolism of therapeutic drugs is caused by cytochrome P450 enzymes. The ‘P450’ is a spectrophotometric term and indicates the enzyme absorbs light at 450 nm.

17. By the end of this lecture, you should: −be able to give examples of periodic trends and chemical properties used to construct the Periodic Table. − explain periodic trends in atomic radii and ionization energies in terms of size and effective nuclear charge. − give examples of essential, toxic and medicinal elements. −be able to complete the worksheet (if you haven’t already done so…) 17 Learning Outcomes:

18. 18 Questions to complete for next lecture: 1.Carbon and lead are both in Group 14. One is a metal and the other a non-metal. a.Outline one physical characteristic and one chemical characteristic of a metal and of a non-metal. b.Explain the trend in metallic properties in Group 14. 2.A reducing agent supplies electrons in a reaction. Which group of the periodic table contains elements that may react as reducing agents. 3.Rank the following atoms in order of increasing size: Ca, Be, C, Br, Cs. 4.Which is the most electronegative element?