1. Periodic trends

2. Atomic Radius
Atomic radius is the distance from the center of an atom’s nucleus to its outermost electron.
Radius

3. Atomic Radius Trend #1 Shielding Effect Hydrogen (1s1)
Atoms get larger going down a group
Lithium (1s2 2s1)
Sodium (1s2 2s2 2p6 3s1)
Shielding Effect

4. Atomic Radius Trend #2 1s2 2s2 2p2 1s2 2s2 2p1 1s2 2s2 2p3
Shrinking Effect

5. Atomic Radii of Representative Elements (nm)Li Be B C N O F Na Mg Al Si P S Cl K Ca Ga Ge As Se Br Sr Rb In Sn Sb Te I Cs Ba Tl Pb Bi Po At

6. Atomic Radius Atomic Radius increases Atomic Radius increases H Li K FNa K Fr F At
Atomic Radius increases

7. Ionization Energy A + E A+ + e-
Energy needed to remove one of atom’s electrons from its outermost shell
A + E A e-
Reflection of how strongly an atom holds onto its outermost electron.
Atoms with high ionization energies hold onto their electrons very tightly.
Atoms with low ionization energies are more likely to lose one or more of their outermost electron.

8. Ionization Energy Ionization energy increasesH Li Na K Fr F At
Ionization energy increases
Ionization energy increases

9. Metallicity
Ability of an atom to lose an electron TREND: Increases from top to bottom Decreases from left to right

10. Electron Affinity A + e- A- + E
Energy released when an atom gains an electron to form a negative ion/anion.
A + e A E
Measure of an atom’s attraction, or affinity, for an extra electron.
Electron affinity increases within a period from left to right. As one goes down a group, electron affinity decreases.

11. Electronegativity
Ability of an atom to attract electrons in a chemical bond. H Li Na K Fr F At
Electronegativity increases
Electronegativity increases

12. Ionic Radius
Anion (negative ion), its size increases, since the nuclear charge remains the same but the repulsion resulting from the additional electron(s) enlarges the domain of the electron cloud.

13. Ionic Radius
Cation (positive ion) smaller than neutral atom, since removing one or more electrons reduces electron-electron repulsion but the nuclear charge remains the same, so the electron cloud shrinks.
From top to bottom of a periodic group both the atomic radius and the ionic radius increases.

14. + Ionic Radius Li F Li+ F--
Changes in size when Li reacts with F to form LiF

15. Tl Pb Ionic Radii of Representative Elements (nm) Rb Cs 1A 2A 3A 4A 5ALi Be O F B C P S Na Cl Mg Al Si As Se K Br Ca Ga Ge Sb Te Rb I Sr In Sn Bi Po Cs At Ba Tl Pb

16. Summary of Periodic Trends
Metallicity inreases
Atomic Radius increases/ Ionic size H Li Na K Fr F At
Electronegativity increases
Electron affinity increases
Ionization energy increases
Metallicity increases
Atomic Radius increases/ ionic size
Electronegativity increases
Ionization energy increases
Electron Affinity increases

17. Challenge
Arrange the following groups of atoms in order of decreasing atomic size:
B, Al, Ga
Sn, Sb, Te
Cd, Si, Ga
As, P, Cl

18. Answers a. Ga, Al, B b. Sn, Sb, Te c. Cd, Ga, Si d. As, P, Cl
e. Cl, O, F

19. Challenge
2. For each of the following pairs, predict which element has (1) the larger radius, and (2) the larger ionization energy:
Na & Cl
C & O
Li & Rb
As & F
Ne & Xe
N & Sb
Sr & Si
Fe & Br

20. Answers (1) Na, (2) Cl (1) C, (2) O (1) Rb, (2) Li (1) As, (2) F
(1) Xe, (2) Ne
(1) Sb, (2) N
(1) Sr, (2) Si
(1) Fe, (2) Br

21. Challenge
3. List the following ions in order of increasing ionic radius: N3-, Na+, F-, Mg2+, O2-
4. Indicate which one of the two species in each of the following pairs is smaller:
Cl or Cl-
Na or Na+
O2- or S2-
Mg2+ or Al3+
Au+ or Au3+