1. Periodic Trends Notable trends of the table

2. What are periodic trends on the periodic table? The predictable pattern by which properties of elements change across or down the periodic table. There are always exceptions to these periodic trends…each of the trends is a “general” trend as you move across a period or down a group.

3. Trend 1: Atomic Radii

4. What is atomic radius? Half of the distance between the nuclei of two bonded atoms. H H H H Distance between nuclei Atomic radius of hydrogen atom

5. Atomic Radii Trends Decreases Increases

6. Atomic Radii Trends Reasoning, Part 1 Why do atomic radii decrease across a period? Moving left to right, the number of protons, neutrons and electrons all increase. n n e e p p n n e e p p n n e e p p n n e e n n p p p p e e p p n n p p n n e e e e Move across the periodic table Lithium atomBeryllium atom As the # of protons and neutrons increase, the attraction between the positive nucleus and negative electron cloud increases. Radius decreases This attraction “pulls” in on the electrons. Think of this as being similar to how larger planets have a greater pull on their objects!

7. Atomic Radii Trends Reasoning, Part 2 Why do atomic radii increase down a group? Protons, neutrons and electrons are also added as you move down a group. Move down the periodic table Lithium atom Sodium atom However, the electrons are added in new energy levels. Radius increases The inner electrons “shield” the new outer electrons from the pull of the nucleus, therefore it doesn’t pull in like the last slide. + e e e e e e e e e e e e e e e e e e e e e e e e e e e e +

8. Atomic Radius

9. Trend 2: Ionization Energy

10. What is Ionization Energy? The energy needed to remove the outermost electron.

11. Ionization Energy Trends Increases Decreases

12. Ionization Energy Trends Reasoning, Part 1 Why does Ionization Energy increase across a period? Moving left to right, the radius of the atom decreases as more protons pull on more electrons. n n e e p p n n e e p p n n e e p p n n e e n n p p p p e e p p n n p p n n e e e e Move across the periodic table Lithium atomBeryllium atom When an atom is smaller, the electrons are closer to the nucleus, and therefore feel the pull more strongly. Radius decreases It is harder to pull electrons away from these smaller atoms. IE increases

13. Ionization Energy Trends Reasoning, Part 2 Why does ionization energy decrease down a group? As you move down a group, the radius increases as more electrons shells are added. Move down the periodic table Lithium atom Sodium atom As the outer electrons (those involved in bonding) are farther from the nucleus, they will feel the “pull” of the nucleus less. Radius increases It is easier to remove an electron from a larger atom. + e e e e e e e e e e e e e e e e e e e e e e e e e e e e + IE decreases

14. Ionization Energy

15. Ionic Charge & Radii

16. Review Some Definitions Ion – atom with a charge. Cation – positively charged ion. Results from loss of electrons. Anion – negatively charged ion. Results from gain of electrons.

17. Ionic Radii—Cations How does the radius of a cation compare to the parent atom? Atoms lose electrons to create positive ions Creating a cation, losing electrons Lithium atomLi + ion When electrons are lost, there are now more protons than electrons Radius decreases Therefore, the protons have a greater “pull” on each of the electrons. e e e e e e + e e e e +

18. Ionic Radii—Anions How does the radius of an anion compare to the parent atom? Atoms gain electrons to create negative ions Creating an anion, gaining electrons Oxygen atomO 2- ion When electrons are gained, there are now more electrons than protons Radius increases Therefore, the protons have a weaker “pull” on each of the electrons. e e e e e e + e e e e e e e e e e e e e e e e + e e e e e e e e e e e e e e

19. Summary of Periodic Trends Atomic radius decreases Ionization energy Increases Atomic radius increases Ionization energy decreases 1 234 5 67 8

20. Let’s Practice Example: List Li, Cs and K in order of increasing Atomic radii Ionization Energy Example: List Li, N and C in order of increasing Atomic radii Ionization Energy

21. Let’s Practice Example: List Li, Cs and K in order of increasing Atomic radii Ionization Energy Example: List Li, N and C in order of increasing Atomic radii Ionization Energy Li, K, Cs Cs, K, Li N, C, Li Li, C, N