1. 1 Chapter 7 Atomic Structure

2. 2 Periodic Trends n Ionization energy the energy required to remove an electron form a gaseous atom n Highest energy electron removed first. First ionization energy ( I 1 ) is that required to remove the first electron. First ionization energy ( I 1 ) is that required to remove the first electron. Second ionization energy ( I 2 ) - the second electron Second ionization energy ( I 2 ) - the second electron n etc. etc.

3. 3 Trends in ionization energy n for Mg I 1 = 735 kJ/moleI 1 = 735 kJ/mole I 2 = 1445 kJ/moleI 2 = 1445 kJ/mole I 3 = 7730 kJ/moleI 3 = 7730 kJ/mole n The effective nuclear charge increases as you remove electrons. n It takes much more energy to remove a core electron than a valence electron because there is less shielding

4. 4 Explain this trend n For Al I 1 = 580 kJ/moleI 1 = 580 kJ/mole I 2 = 1815 kJ/moleI 2 = 1815 kJ/mole I 3 = 2740 kJ/moleI 3 = 2740 kJ/mole I 4 = 11,600 kJ/moleI 4 = 11,600 kJ/mole

5. 5 Across a Period Generally from left to right, I 1 increases because Generally from left to right, I 1 increases because n there is a greater nuclear charge with the same shielding. As you go down a group I 1 decreases because electrons are further away and there is more shielding As you go down a group I 1 decreases because electrons are further away and there is more shielding

6. 6 It is not that simple Z eff changes as you go across a period, so will I 1 Z eff changes as you go across a period, so will I 1 n Half-filled and filled orbitals are harder to remove electrons from n here’s what it looks like

7. 7 First Ionization energy Atomic number

8. 8 First Ionization energy Atomic number

9. 9 First Ionization energy Atomic number

10. 10 Atomic Size n First problem where do you start measuring n The electron cloud doesn’t have a definite edge. n They get around this by measuring more than 1 atom at a time

11. 11 Atomic Size n Atomic Radius = half the distance between two nuclei of a diatomic molecule } Radius

12. 12 Trends in Atomic Size n Influenced by two factors n Shielding n More shielding is further away n Charge on nucleus n More charge pulls electrons in closer

13. 13 Group trends n As we go down a group n Each atom has another energy level n So the atoms get bigger H Li Na K Rb

14. 14 Periodic Trends n As you go across a period the radius gets smaller. n Same energy level n More nuclear charge n Outermost electrons are closer NaMgAlSiPSClAr

15. 15 Overall Atomic Number Atomic Radius (nm) H Li Ne Ar 10 Na K Kr Rb

16. 16 Electron Affinity n The energy change associated with adding an electron to a gaseous atom n High electron affinity gives you energy- n exothermic n More negative n Increase (more - ) from left to right –greater nuclear charge. n Decrease as we go down a group –More shielding

17. 17 Ionic Size n Cations form by losing electrons n Cations are smaller than the atom they come from n Metals form cations n Cations of representative elements have noble gas configuration.

18. 18 Ionic size n Anions form by gaining electrons n Anions are bigger than the atom they come from n Nonmetals form anions n Anions of representative elements have noble gas configuration.

19. 19 Configuration of Ions n Ions always have noble gas configuration n Na is 1s 2 2s 2 2p 6 3s 1 n Forms a 1+ ion - 1s 2 2s 2 2p 6 n Same configuration as neon n Metals form ions with the configuration of the noble gas before them - they lose electrons

20. 20 Configuration of Ions n Non-metals form ions by gaining electrons to achieve noble gas configuration. n They end up with the configuration of the noble gas after them.

21. 21 Group trends n Adding energy level n Ions get bigger as you go down Li +1 Na +1 K +1 Rb +1 Cs +1

22. 22 Periodic Trends n Across the period nuclear charge increases so they get smaller. n Energy level changes between anions and cations Li +1 Be +2 B +3 C +4 N -3 O -2 F -1

23. 23 Size of Isoelectronic ions n Iso - same n Iso electronic ions have the same # of electrons n Al +3 Mg +2 Na +1 Ne F -1 O -2 and N -3 n all have 10 electrons n all have the configuration 1s 2 2s 2 2p 6

24. 24 Size of Isoelectronic ions n Positive ions have more protons so they are smaller Al +3 Mg +2 Na +1 Ne F -1 O -2 N -3

25. 25 Electronegativity

26. 26 Electronegativity n The tendency for an atom to attract electrons to itself when it is chemically combined with another element. n How “greedy” n Big electronegativity means it pulls the electron toward itself. n Atoms with large negative electron affinity have larger electronegativity.

27. 27 Group Trend n The further down a group more shielding n Less attracted (Z eff ) n Low electronegativity.

28. 28 Periodic Trend n Metals are at the left end n Low ionization energy- low effective nuclear charge n Low electronegativity n At the right end are the nonmetals n More negative electron affinity n High electronegativity n Except noble gases

29. 29 Ionization energy, electronegativity Electron affinity INCREASE

30. 30 Atomic size increases, Ionic size increases

31. 31 Parts of the Periodic Table

32. 32 The information it hides n Know the special groups n It is the number and type of valence electrons that determine an atom’s chemistry. n You can get the electron configuration from it. n Metals lose electrons have the lowest IE n Non metals- gain electrons most negative electron affinities

33. 33 The Alkali Metals n Doesn’t include hydrogen- it behaves as a non-metal n decrease in IE n increase in radius n Decrease in density n decrease in melting point n Behave as reducing agents

34. 34 Reducing ability n Lower IE< better reducing agents n Cs>Rb>K>Na>Li n works for solids, but not in aqueous solutions. n In solution Li>K>Na n Why? n It’s the water -there is an energy change associated with dissolving

35. 35 Hydration Energy n Li + (g) → Li + (aq) is exothermic n for Li + -510 kJ/mol n for Na + -402 kJ/mol n for K + -314 kJ/mol n Li is so big because of it has a high charge density, a lot of charge on a small atom. n Li loses its electron more easily because of this in aqueous solutions

36. 36 The reaction with water n Na and K react explosively with water n Li doesn’t. Even though the reaction of Li has a more negative  H than that of Na and K Even though the reaction of Li has a more negative  H than that of Na and K n Na and K melt  H does not tell you speed of reaction  H does not tell you speed of reaction n More in Chapter 12.