Ken Rogers Miami Killian

1. Periodic Trends Ken Rogers Miami Killian

2. We are going to be studying some of the properties of the atoms. 1. atomic size 2. ionization energy 3. electron affinity 4. electronegativity

3. 1. Atomic Size

4. The size of an atom is measured by its radius. (from the nucleus to the outermost orbital) However, this is not a definite boundary. ? So the outside is determined by bonding an identical atom and the distance between the two atoms is measured.

5. atomic radius – half the distance between the nuclei of two identical atoms that are bonded. 0.32 nm 0.16 nm 0.16 nm atomic radius = 0.16 nm

6. You won’t be asked for the size of the atoms, but given two atoms, you will be asked which is bigger. How you do this is by learning the pattern or trend for the size of the atoms. For each of those four properties listed, there will be a periodic trend and a group trend. periodic trend - the type of change going from left to right (through a period). group trend - the type of change going down a column of elements (down a group).

7. 1 energy level The group trend for atomic size is: Atomic size increases down a group. 2 energy levels 3 energy levels because of the increasing # of energy levels 4 energy levels

8. Group Trend is . . Atomic size increases

9. What is the periodic trend?

10. 17p+ 17e- 16p+ 16e- 11p+ 11e- 14p+ 14e- 13p+ 13e- 12p+ 12e- 15p+ 15e- Periodic trend Here are some of the elements in the third period. The atoms have more subatomic particles as you go from left to right. Wrong Na Mg Al Si P S Cl You might think the atoms get bigger.

11. 17p+ 17e- 16p+ 16e- 11p+ 11e- 14p+ 14e- 13p+ 13e- 12p+ 12e- 15p+ 15e- Let’s try again. Since they’re all in the third row, they all have 3 principal energy levels. So, maybe they’re all the same size. Wrong Na Mg Al Si P S Cl

12. It’s true they have more protons, electrons, and even more neutrons. But the pull of the protons on the orbiting electrons is stronger as you go from left to right. 11p+ 12p+ Na Mg

13. 17p+ 16p+ 11p+ 14p+ 13p+ 12p+ 15p+ Periodic trend Here’s the correct trend. The atomic size decreases from left to right. Na Mg Al Si P S Cl Due to the increasing nuclear charge.

14. Atomic Size (nm) Li F O C N B Be 0.066 0.064 0.070 0.111 0.077 0.152 0.088 Al Si Na Mg Cl P S 0.160 0.117 0.099 0.110 0.186 0.143 0.104 As Ga Se Br Ge Ca K 0.116 0.122 0.115 0.121 0.122 0.231 0.197 Sb Te I Sn In Sr Rb 0.137 0.133 0.151 0.165 0.14 0.215 0.244 Po Bi At Tl Pb Ba Cs 0.175 0.140 0.217 0.155 0.171 0.164 0.262

15. 2. Ionization Energy

16. energy 11 p+ 11 e- 10 e- e- positive ion atom +1 An electron can be removed from an atom if enough energy is added.

17. 11 p+ 11 p+ + energy 10 e- 11 e- +1 Ionization Energy ionization energy – the energy required to remove one electron from a neutral atom. + e- or more simply A + energy a A+ + e-

18. It requires less energy to remove an electron the further away it is from the nucleus. The electrons in the inner energy levels shield the attraction of the nucleus for its outer electrons. Ionization energy decreases down a group.

19. 17p+ 16p+ 11p+ 14p+ 13p+ 12p+ 15p+ Across a period, the electrons are closer and the nuclear charge stronger. The electrons are held more tightly and it requires more energy to remove the electron. Na Mg Al Si P S Cl Ionization energy (energy needed to remove an electron) increases across a period.

20. down a group through a period 2400 He Ne 2000 1st period F 1600 H Ar N O Ionization Energy (kJ/mol) Cl Kr 1200 C P S 2nd period Br Be B Se 800 As Si Mg Li Ge Al Ca Na Ga 400 K 1 2 13 14 15 16 17 18 Group #

21. Ionization Energies for some elements ( kJ/mole )

24. through a period 2400 Ne 2000 F 1600 N O Ionization Energy (kJ/mol) 1200 C 2nd period Be B 800 Li 400 1 2 13 14 15 16 17 18 Group #

25. 520 Li 1s2 2s1

26. 7298 Li 1s1 1s2

27. 11,815 Li 1s1 7298

28. 7298 11,815 Li 1s22s1 520

29. 900 Be 1s2 2s1 2s2 7298 11,815

30. 1757 Be 1s2 2s1 7298 11,815

31. 14,849 Be 1s1 1s2 1757 7298 11,815

32. 21,007 Be 1s1 1757 7298 7298 11,815 14,849

33. B 1s22s2 2p1 1757 7298 7298 11,815 14,849 21,007

34. B 1s22s2 1757 7298 7298 11,815 14,849 21,007

35. B 1s22s1 1757 7298 7298 11,815 14,849 21,007

36. B 1s2 1757 7298 7298 11,815 14,849 21,007

37. B 1s1 1757 7298 11,815 14,849 21,007

38. B 1757 7298 11815 14849 21007

39. C 1s22s2 2p2

40. C 1s22s2 2p2

41. C 1s22s2 2p2

42. Principal Energy Levels 1st 2nd Sublevels Outer Shell electrons 1s2 2s2 2p1 Inner Shell electrons

43. 3. Electron Affinity

44. Electron affinity is the energy change associated with the addition of an electron to a neutral atom. It’s a way of measuring the attraction for electrons. When an atom acquires an electron, one of two types of energy changes occurs. If energy has to be added when an atom acquires an electron, the energy change is positive. Having to add energy is a good indication the atom didn’t ‘want’ the electron so it shows lowelectron affinity. A + e- + energy a A-

45. However, if the atom produces energy when an electron is added, it indicates a more stable electron amount. Because the atom loses energy when energy is given off, the energy change is negative. A + e- a A- + energy A negative energy change indicates the atom has a higher electron affinity than an atom that requires energy be added. The more negative the energy change, the higher the electron affinity.

46. Like magnets, the further apart they are, the weaker the attraction. The nucleus isn’t able to attract electrons the further away they are. The ability to attract electrons is also decreased when there are energy levels in between the nucleus and the outer shell where the electron would be added. (shielding affect) Electron affinity decreases down a group.

47. 17p+ 16p+ 11p+ 14p+ 13p+ 12p+ 15p+ Across a period, the electrons are closer and the nuclear charge is stronger. The ability to attract electrons increases. Na Mg Al Si P S Cl Electron affinity increases across a period.

48. 4. Electronegativity

49. Electronegativity – is a measure of an atom’s ability to attract an electron. Because electron affinity is confusing . . . negative electron affinities indicate high e- attraction and positive electron affinities mean low e- attraction another way of measuring e- attraction was devised. Although the last property of the four, this is the one that we will be using the most to explain properties of molecules later.

50. increases decreases F Na Mg Al Si P S Cl 17p+ 16p+ 11p+ 14p+ 13p+ 12p+ 15p+ Br Because electronegativity is just another way of measuring electron affinity, the trend is the same for the same reasons. I At