Chemical Structure: Structure of Matter. Elements, Ions & Isotopes

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Lecture materials for the Introductory Chemistry course for Forensic Scientists, University of Lincoln, UK. See http://forensicchemistry.lincoln.ac.uk/ for more details.

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Chemical Structure: Structure of Matter. Elements, Ions & Isotopes

  1. 1. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Elements, Ions & Isotopes University of Lincoln presentation
  2. 2. What you should know… <ul><li>Elements and their classification </li></ul><ul><li>Atoms/molecules </li></ul><ul><li>Symbols of the elements </li></ul><ul><li>Allotropy </li></ul><ul><li>The Octet rule </li></ul><ul><li>Ions – cations/anions </li></ul><ul><li>Oxidation/reduction </li></ul><ul><li>Ionisation energy/electron affinity </li></ul><ul><li>Isotopes </li></ul><ul><li>Atomic mass </li></ul><ul><li>Relative atomic mass </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  3. 3. 1. Elements This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  4. 4. IUPAC Definition <ul><li>An element is matter, </li></ul><ul><li>all of whose atoms are alike </li></ul><ul><li>in having the same positive charge </li></ul><ul><li>on the nucleus </li></ul><ul><li>International Union of Pure and Applied Chemistry </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  5. 5. Dictionary Definition <ul><li>A substance that cannot be decomposed </li></ul><ul><li>into simpler substances </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  6. 6. Are all elements simply collections of atoms? <ul><li>YES, normally </li></ul><ul><li> Elemental mercury (liquid), Hg </li></ul><ul><li>Elemental </li></ul><ul><li>copper, Cu </li></ul><ul><li> Elemental </li></ul><ul><li> helium (gas), He </li></ul><ul><li>Elemental </li></ul><ul><li>gold, Au </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  7. 7. Some elements only exist as molecules <ul><li>These elements exist as diatomic molecules* </li></ul><ul><li>* A molecule is two or more atoms bonded together </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License H 2 N 2 O 2 F 2 Cl 2 Br 2 I 2
  8. 8. Symbols <ul><li>A = MASS NUMBER </li></ul><ul><li>Z = ATOMIC NUMBER </li></ul><ul><li>=number of protons </li></ul><ul><li>N =number of neutrons </li></ul><ul><li>A = N + Z </li></ul><ul><li>X </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Z A
  9. 9. For Example This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License 20 40 11 22 1 1 H Na Ca
  10. 10. Classification of elements <ul><li>Metals </li></ul><ul><li>Non-metals </li></ul><ul><li>Semi-metals </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  11. 11. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License H Be Li Na K Rb Cs Fr Mg Ca Sr Ba Ra Sc Y La Ac Ti V Cr Mn Fe Co Ni Cu Zn Zr Hf Ta W Re Os Ir Pt Au Hg Tl Nb Mo Tc Ru Rh Pd Ag Cd In Sn Pb Bi Po At Rn Xe Kr Ar Ne Sb Te I Ga Al Ge Si P S Cl As Se Br Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr He B C N O F Metals Semi-metals Non-Metals Classification of elements
  12. 12. Allotropes <ul><li>Some elements exist in more than one structural form. This property is called ALLOTROPY </li></ul><ul><li>Consider carbon – 2 common allotropes are graphite and diamond. </li></ul><ul><li>Both consist only of atoms of carbon, C, but their structures are very different, and hence their properties differ </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  13. 13. Allotropes of Carbon This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License C 60 fullerene structure Graphite layered structure Diamond structure
  14. 14. Allotropes of other elements? <ul><li>Tin, Sn </li></ul><ul><li>Phosphorus, P </li></ul><ul><li>Arsenic, As </li></ul><ul><li>Oxygen, O </li></ul><ul><li>Sulphur, S </li></ul><ul><li>Selenium, Se </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  15. 15. 2. Ions This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  16. 16. The Octet Rule <ul><li>Because filled orbitals give the best STABILITY , all elements try to attain a noble gas configuration </li></ul><ul><li>(i.e. 8 electrons in their valence shell) </li></ul><ul><li>2 ways of doing this: </li></ul><ul><li>(i) losing electrons; or </li></ul><ul><li>(ii) gaining electrons </li></ul><ul><li>(which ever uses the least energy) </li></ul><ul><li>This is the driving force behind the chemistry of the elements and is called the OCTET RULE </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  17. 17. The Periodic Table This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License n=1 n=2 n=3 n=4 n=5 n=6 n=7 The Periodic Table consists of rows of 8 elements (s + p block only) Each row corresponds to a different quantum number (n=1–7) Each column has the same VALENCE CONFIGURATION ns 1 ns 2 ns 2 np 1 ns 2 np 2 ns 2 np 3 ns 2 np 4 ns 2 np 5 ns 2 np 6 f - block elements H Be Li Na K Rb Cs Fr Mg Ca Sr Ba Ra Sc Y La Ac Ti V Cr Mn Fe Co Ni Cu Zn Zr Hf Ta W Re Os Ir Pt Au Hg Tl Nb Mo Tc Ru Rh Pd Ag Cd In Sn Pb Bi Po At Rn Xe Kr Ar Ne Sb Te I Ga Al Ge Si P S Cl As Se Br Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr He B C N O F Lanthanoids Actinoids d – block elements Hydrogen and s – block elements p – block elements
  18. 18. Definition <ul><li>An ION is a charged atom or molecule. </li></ul><ul><li>There are 2 types of ion: </li></ul><ul><li>A CATION is positively charged </li></ul><ul><li>An ANION is negatively charged </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  19. 19. Cations <ul><li>Cations are formed when an atom loses 1 or more valence electron: </li></ul><ul><li>Na  Na + + e - </li></ul><ul><li>Mg  Mg 2+ + 2e - </li></ul><ul><li>The loss of electrons is known as OXIDATION and is a typical reaction of metals </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  20. 20. Valence Electrons This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License [Ar] 4s 2 Ca 20 1s 2 2s 2 2p 6 Ne 10 [Ar] 4s 1 K 19 [He] 2s 2 2p 5 F 9 1s 2 2s 2 2p 6 3s 2 3p 6 Ar 18 [He] 2s 2 2p 4 O 8 [Ne] 3s 2 3p 5 Cl 17 [He] 2s 2 2p 3 N 7 [Ne] 3s 2 3p 4 S 16 [He] 2s 2 2p 2 C 6 [Ne] 3s 2 3p 3 P 15 [He] 2s 2 2p 1 B 5 [Ne] 3s 2 3p 2 Si 14 [He] 2s 2 Be 4 [Ne] 3s 2 3p 1 Al 13 [He] 2s 1 Li 3 [Ne] 3s 2 Mg 12 1s 2 He 2 [Ne] 3s 1 Na 11 1s 1 H 1 Electronic configuration Element Symbol Atomic number Electronic configuration Element Symbol Atomic number
  21. 21. <ul><li>Group 1 = [NG] ns 1 </li></ul><ul><li>Group 2 = [NG] ns 2 </li></ul><ul><li>Elements in these groups want to LOSE their outer (valence) electrons to gain the noble gas configuration [NG]: </li></ul><ul><li>Na  Na + + e - </li></ul><ul><li>Mg  Mg 2+ + 2e - </li></ul><ul><li>Electronic configuration of both cations = [Ne] </li></ul><ul><li>The energy required to remove a valence electron is called the IONISATION ENERGY </li></ul>Group 1 & 2 elements (metals) This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Group 1 Group 2 Ra Fr Ba Cs Sr Rb Ca K Mg Na Be Li
  22. 22. Anions <ul><li>Anions are formed when an atom gains 1 or more valence electron: </li></ul><ul><li>F + e -  F - </li></ul><ul><li>O + 2e -  O 2- </li></ul><ul><li>The gain of electrons is known as REDUCTION and is a typical reaction of non-metals </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  23. 23. <ul><li>Group 16 = [NG] ns 2 np 4 </li></ul><ul><li>Group 17 = [NG] ns 2 np 5 </li></ul><ul><li>Elements in these groups want to GAIN valence electrons to attain the noble gas configuration [NG] ns 2 np 6 , which is the noble gas sitting on their RHS in the Periodic Table </li></ul><ul><li>F + e -  F - </li></ul><ul><li> O + 2e -  O 2- </li></ul><ul><li>Electronic configuration of both anions = [Ne] </li></ul><ul><li>Electron affinity is a measure of how easy it is to gain a valence electron </li></ul>Group 16 & 17 elements (non-metals) This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Groups 16 17 18 Se S O At I Br Cl F Rn Xe Kr Ar Ne
  24. 24. 3. Isotopes This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  25. 25. Definition <ul><li>In 1913 Soddy proposed the existence of ISOTOPES </li></ul><ul><li>Definition : Atoms of the same elements with different atomic masses </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Frederick Soddy Nobel Prize (Chemistry) 1921
  26. 26. Definition <ul><li>Isotopes of an element have the same number of protons, but different numbers of neutrons </li></ul><ul><li>Eg. </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License 29 29 Mass number (A) Atomic number (Z) Protons (Z) = 29 Neutrons (N) = 34 Protons (Z) = 29 Neutrons (N) = 36 Cu Cu 65 63
  27. 27. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Henri Becquerel Marie & Pierre Curie Radioactivity discovered in 1896
  28. 28. Stable v. Radioactive Isotopes This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License There are approximately 1,700 isotopes known to exist
  29. 29. Chart of the nuclides This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  30. 30. Chart of the nuclides This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Black squares denote STABLE isotopes Z N
  31. 31. Atomic Mass, A <ul><li>For simplicity, atomic masses are given relative to the mass of 12 C </li></ul><ul><li>12 C = 12.0000 amu </li></ul><ul><li>amu = atomic mass unit = 1.660x 10 -27 kg </li></ul><ul><li>similar to the mass of a proton or neutron (see Lecture 1) </li></ul><ul><li>Mass number (A) is used as the atomic mass </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
  32. 32. Relative Atomic Mass, A r This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Mg 24 78.7 Mg 25 10.1 Mg 26 11.2 % abundance The relative atomic mass of an element is the weighted mean of the atomic masses of all the stable isotopes for that element. For example: A r (Mg) = 24.3 Atomic mass
  33. 33. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Acknowledgements <ul><li>JISC </li></ul><ul><li>HEA </li></ul><ul><li>Centre for Educational Research and Development </li></ul><ul><li>School of natural and applied sciences </li></ul><ul><li>School of Journalism </li></ul><ul><li>SirenFM </li></ul><ul><li>http:// tango.freedesktop.org </li></ul>

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