1. Periodic Trends Atomic Radius Ionic Radius Ionization Energy Electronegativity

2. Atomic Radius  Atomic Radius is used to estimate the size of the atom.  Atomic Radius is half the distance between two nuclei of identical atoms that are adjacent to each other.  Why?

3. Atomic Radius - Periodic Trends  Notice atomic radii increase as we go down a group.  Why?  Notice atomic radii decrease as we go across a period from left to right even though we’re adding particles to the succeeding atoms.  Why? As we add more energy levels, size of atom increases As we move across period, atomic # increases, so electrons in s and p sublevels are pulled closer to the more highly charged + nucleus -> smaller radius

4. Ionic Radius  An ion is an atom or molecule that has gained or lost an electron. Which elements tend to gain electrons and which tend to lose electrons?  A ca t ion is a positive ion  How could an atom have a positive charge?  A negative ion is called an anion.  How could an atom have a negative charge?  Atoms – lose electrons,+ ions, smaller radius  Atoms – gain electrons, -ions, larger radius  Trend??? As you go down a Group, the ionic radius increases. As you go across a Period, the ionic radius decreases, then increases, then decreases again.

5. Ionization Energy  Ionization energy is the energy required to remove an electron from an atom.  Can you predict which elements would require the least energy to remove an electron and which would require the most?  Examples.

6. Ionization Energy  The I.E. increases as you move across period because of increased nuclear charge. The higher the + charge, the more strongly the nucleus attracts electrons.  The I.E. decreases as you move down a group. The electrons in higher energy levels are farther from the nucleus making them easier to remove.

7. Ionization Energy  Factors affecting ionization energies include:  Nuclear charge - The larger the nuclear charge the greater the ionization energy.  Shielding effect - The greater the shielding effect, the less the ionization energy.  Radius - The greater the distance between the nucleus and the outer electrons of an atom, the less the ionization energy.

8. Shielding Effect Nucleus e-e- e-e- e-e- Inner (shielding) energy levels Outermost energy level with valence electron e-e- Nuclear force absorbed by inner Energy level electrons e-e- e-e-

9. Practice problems  Page 165 #16-17

10. Electronegativity  Electronegativity is the measure of an atom to attract electrons in a chemical bond.  Electronegativity decreases as you go down a group and increases as you go across a period from left to right.  Why?