1. Periodic Trends Modified from Mrs. Coyle Chemistry

2. Part I – Atomic Size

3. Atomic Radius Measures as distance from nucleus to nucleus and divided by 2. Unit commonly used is pm picometer= 10 -12 m Example: iodine atomic radius 140pm

4. Draw C and N Include number of protons in the nucleus Include principle energy levels drawn as orbits around the nucleus Include the correct number of electrons in each principle energy level

5. How does atomic radius change across a period? It is smaller to the right. Why do you think so? Use your drawings to help you! More protons in the nucleus  higher electrical force pulls electrons closer to nucleus.

6. Draw C and Si Include number of protons in the nucleus Include principle energy levels drawn as orbits around the nucleus Include the correct number of electrons in each principle energy level

7. How does atomic radius change down a group? It is larger down the group. Why do you think it is? Use your drawings to help you. Valence electrons are at higher energy levels and are not bound as tightly to the nucleus because they are screened or shielded ( pushed away) by other electrons in inner levels.

8. Note There are some exceptions. Example column 13.

9. The Periodic Table and Atomic Radius

10. Draw the elements F and Li Include number of protons in the nucleus Include principle energy levels drawn as orbits around the nucleus Include the correct number of electrons in each principle energy level

11. Example: Which is larger: a lithium atom or a fluorine atom? Why do you think that? Use your drawings to help you. A lithium atom

12. Example: Which is larger: an arsenic atom or a sulfur atom? An arsenic atom

13. Part II – Ionization Energy

14. Ionization energy Ionization energy is the amount of energy needed to remove an electron from a gaseous atom. First ionization energy – 1+ Second ionization energy – 2+

15. Ion Positive ion---removal of electron Negative ion--- addition of electron

16. Draw O and S Include number of protons in the nucleus Include principle energy levels drawn as orbits around the nucleus Include the correct number of electrons in each principle energy level

17. Is it easier to remove an electron from O or S? Why do you think that?

18. How does ionization energy change down a group? The first ionization energy decreases as you move down a group. Why? The size of the atom increases. Electron is further from the nucleus.

19. Draw O and N Include number of protons in the nucleus Include principle energy levels drawn as orbits around the nucleus Include the correct number of electrons in each principle energy level

20. The first ionization energy increases as you move from left to right across a period. Why? Nuclear charge increases while shielding is constant. Attraction of the electron to the nucleus increases. Does N or O have a higher ionization energy? Why?

22. Part III: Ionic size Metallic elements easily lose electrons. Non-metals more readily gain electrons. How does losing or gaining an electron effect the size of the atom (ion) ?

23. Positive ions Positive ions are always smaller that the neutral atom. Loss of outer shell electrons.

24. Negative Ions Negative ions are always larger than the neutral atom. Gaining electrons.

25. Ion size trends in periods. Going from left to right there is a decrease in size of positive ions. Starting with group 5, there is sharp increase followed by a decrease in the size of the anion as you move from left to right.

26. Ion size trends in columns. Ion size increases as you move down a column for both positive and negative ions

27. Electronegativity: the ability of an atom in a bond to pull on the electron. (Linus Pauling)

28. Electronegativity When electrons are shared by two atoms a covalent bond is formed. When the atoms are the same they pull on the electrons equally. Example, H-H. When the atoms are different, the atoms pull on the electrons unevenly. Example, HCl

29. Trends in Electronegativity Electronegativity generally decreases as you move down a group. Electronegativity of the representative elements (Group A elements) increases as you move across a period.

30. Why is F more electronegative than I? Draw the elements F and I Include number of protons in the nucleus Include principle energy levels drawn as orbits around the nucleus Include the correct number of electrons in each principle energy level

31. Electronegativities of Some Elements Element Pauling scale F 4.0 Cl 3.0 O 3.5 N 3.0 S 2.5 C 2.5 H 2.1 Na 0.9 Cs0.7

32. Note Most electronegative element is F (EN 4.0) Least electronegative stable element is Cs (EN 0.7)

33. Summary Shielding is constant Atomic Radius decreases Ionization energy increases Electronegativity increases Nuclear charge increases Shielding increasesAtomic radius increasesIonic size increasesIonization energy decreasesElectronegativity decreases