1. Trends in the Periodic Table

2. Atomic radius The best measure of atomic radius is the bond radius. Measure the distance between the nuclei of 2 atoms bonded together and divide by two.

3. Going down a group, the atomic radius increases.  Larger atoms have more electrons farther away from the nucleus.  The inner electrons shield the outer electrons from the full effect of the positive charge of the nucleus.

4. Going across a period, the atomic radius decreases  Electrons are being added to the same principal energy level.  For every added electron, a proton is also being added to the nucleus, increasing the charge, pulling the electrons tighter in.  This change is not as noticeable with heavier elements (inner electrons shield).

6. Ionization Energy The energy required to remove an electron from an atom in the gas phase There is a series of ionization energies for each electron removed. These energies get higher for each subsequent electron. The trends given are for the first electron removed.

7. Going down a group, the ionization energy decreases.  Electrons are further out, so the nuclear charge is not felt as strongly.  Shielding effect contributes.

8. Going across a period, the ionization energy increases.  For every added electron, a proton is also being added to the nucleus, increasing the charge.  The same principal energy level is being filled, so the shielding effect is a constant. There are some exceptions to this trend, normally in cases of full or half-full energy sublevels.

10. Electron Affinity Measures how much an atom “wants” to gain electrons Is the change in energy associated with gaining an electron  High electron affinity: really “wants” to gain an electron-  E is a negative number with a high absolute value  e.g. F:  E = -328.5 kJ/mole  Low electron affinity: doesn’t “want” to gain an electron  e.g. Noble gases: have positive values of  E

11. Going down a group, the electron affinity decreses  Shielding more than offsets the increase in nuclear charge Going across a period, the electron affinity increases (  E becomes more negative).  Shielding remains constant, the nuclear charge increases EXCEPTION: The noble gases have the lowest electron affinities of all.