Periodic Trends

1. Periodic Trends Organization of the Periodic Table

3. GROUPS • Columns of the periodic table • Atoms of elements in the same group have the same # of valence electrons and therefore behave similarly PERIODS • Rows of the periodic table • All elements in a period have • their valence electrons in the same energy level.

4. Which of the following are in the same group? • H, He, C, Li • K, Ca, As, Br • He, Ne, Kr, Ar • B, Al, Ge, Sn

5. Which of the following are in the same period? • H, He, C, Li • K, Ca, As, Br • He, Ne, Kr, Ar • B, Al, Ge, Sn

6. Representative and Transition Elements

7. Valence Electrons • Valence Electrons are electrons in the outermost energy level. • - s or p electrons only (even when d and f electrons are present they are not in the outermost energy level)

8. Electron Dot Diagrams • Electron Dot Diagrams show the valence electrons of an element. • Draw the electron dot diagrams for the following: • Mg N F

9. How many valence electrons are in the halogens? • 1 • 2 • 7 • 8

10. How many valence electrons are in Group 17? • 1 • 2 • 7 • 8

11. How many valence electrons are in zinc and chromium? • 1 • 2 • 7 • 8 • Unable to tell

12. Size of the Atom • Think of a ball of an onion. What happens with each layer? • As you go down the periodic table, the energy levels increase and the size of the radius of the atom increases. (each energy level is like another layer of the onion)

13. Which element has a larger atomic radius: Na or K? • Na • K • Unable to be determined

14. Which element has a larger atomic radius: Br or Cl? • Br • Cl • Unable to be determined

15. Atomic Radius cont. • As you move from left to right in the periodic table, what happens to the number of protons in the nucleus? • What effect do these protons have on the electrons? • What effect do the electrons have on each other?

16. Electron Shielding • Electron Shielding (or Screening) – These inner electrons shield the valence electrons from receiving the entire attractive nuclear charge because they repel the valence electrons.

17. Nuclear Charge and Atomic Radius • Within a period, as you go from left to right, the positive nuclear charge increases, and attracts the electrons more strongly. • As the electrons are more attracted to the nucleus, the atomic radius decreases. • Summary: as you go from left to right, the atomic radius generally decreases.

19. Which element has a larger atomic radius: Li or Be? • Li • Be • Unable to be determined

20. Which element has a larger atomic radius: Si or Ar? • Si • Ar • Unable to be determined

21. Which element has a larger atomic radius: Be or Mg? • Be • Mg • Unable to be determined

22. Which element has a larger atomic radius: Si or C? • C • Si • Unable to be determined

24. Octet Rule • The octet rule states that all atoms attempt to become stable by having a full valence electron shell (generally 8 electrons, hence octet rule). • Atoms will gain, lose, or share electrons in order to attain this stability.

25. Which group already has a full octet? • Alkali metals • Transition metals • Halogens • Noble Gases

26. Which group is one electron away from a full octet? • Alkali metals • Transition metals • Halogens • Alkaline earth metals • Both alkali metals and halogens • Noble gases • Both alkali metals and alkaline earth metals

27. Ionization Energy • Electrons are held in atoms by their attraction to the positively charged nucleus. • To remove an electron requires energy. • Ionization energy is the energy required to remove the least tightly bound (or outermost) electron from an atom.

28. Ionization Energy cont. • Compare Li and K. • How many valence electrons? • What is the relative size of the atoms? • Which has a higher ionization energy?

29. Ionization Energy • As you go down a group, the ionization energy decreases because it takes less energy to remove an electron. • The least tightly bound electrons are further from the positive nucleus, and can therefore be removed more easily.

31. Which group has a higher ionization energy? • Halogens • Alkali Metals • Alkaline Earth Metals • All the same

32. Which element has a higher ionization energy? • Li • Be • F • Ne

33. Which element has the lowest ionization energy? • Na • Mg • S • Ar

35. Summary • Ionization energy generally decreases as you go down a group and from right to left in a period.

36. Ionization energy

37. A Quick Review …

38. How many valence electrons does oxygen have? • 1 • 3 • 4 • 6 • 8

39. Which has the biggest atomic radius? • K • Na • Li • Be • Cs • Ca • F

40. What is the effective nuclear charge on lithium? • 1 • 2 • 3 • None of the above

41. Which has the greatest ionization energy? • K • Na • Li • Be • Cs • Ca • F

42. How many valence electrons are in group 14? • 1 • 4 • 7 • 14

43. Second, Third, etc. Ionization Energy • Second ionization is the energy required to remove a second electron. • Ex. Sodium has a lower (first) ionization energy than Magnesium but Mg has a lower second ionization energy than Na. • Why?

44. Which has a lower third ionization energy? • K • Ca • Ga • C

45. Electronegativity • Electronegativityis the tendency of an element to attract electrons in a bond. • Therefore, elements that want to gain electrons will have higher electronegativity. attractive

46. Which group of elements is most likely to gain electrons to become stable? • Alkali Metals • Transition Metals • Halogens • Noble Gases

48. Which has the greatest electronegativity? • K • Na • Li • Be • Cs • Ca • F

49. Which group has the lowest electronegativity (not counting noble gases)? • Alkali metals • Alkaline earth metals • Halogens • Transition Metals