1. Chapter 6 Section 3: Periodic Trends

2. Objectives
Describe and explain the reasons for the trends in Atomic Radius, Ionization Energy, Ionic Radius, and Electronegativity across a period and down a group in the periodic table.

3. Block Periodic Table

4. Electron Configuration and Periodic Properties
Atomic Radius = one-half the distance between the nuclei of identical atoms bonded together
Period – radius decreases as you move left to right (more + charge)
Group – radius increases as you move top to bottom (more energy levels)

5. Trends in Atomic Radius (Size)
The figure below summarizes the group and period trends in atomic size.

6. Electron Configuration and Periodic Properties
1st Ionization Energy – the energy required to remove one electron from a neutral atom
Period – IE increases as you move left to right (higher nuclear charge)
Group – IE decreases as you move top to bottom (more shielding)

7. Trends in Ionization Energy
The figure below summarizes the group and period trends for the first ionization energy.
Energy generally increases
Energy generally decreases

8. Electron Configuration and Periodic Properties
Ionic Radius – specific to the type of ion formed
Metals form Cations which are positive (lose e-) so they are comparatively smaller as ions versus the neutral atom’s radius
Nonmetals form anions which are negative (gain e-) thus are larger than the neutral atom’s radius
Electrons that are gained, lost, or shared in the formation of chemical compounds are called valence electrons

9. Electron Configuration and Periodic Properties
Ionic Radius
Decreases across a period for metals, then nonmetals (higher nuclear charge; constant shielding)
Increases down a group (more energy levels = more shielding)

10. Trends in Ionic Size
The figure below summarizes the group and period trends in ionic size.
Size of cations decreases
Size of anions decreases
Size generally increases

11. Electron Configuration and Periodic Properties
Electronegativity – a measure of the atoms ability in a chemical compound to attract electrons
Period – increases as you move left to right (tend to gain e- not lose them)
Group – decreases as you move top to bottom (easier to lose e- if they are farther away from the nucleus)

12. Trends in Electronegativity
The figure below summarizes the group and period trends for electronegativity
Electronegativity increases
Electronegativity decreases

13. This figure summarizes several trends that exist among the elements.