1. ELECTRON CONFIGURATIONS and PERIODIC PROPERTIES

2. MAIN GROUP ELEMENTS Atomic Radii - One half the distance between the nuclei of identical atoms that are bonded together.
PERIOD TRENDS- Atomic radii tend to GET SMALLER across a period due to the increasing positive charge of the nucleus.
This difference is offset as we move across a period due to the increasing number of electrons and their repulsive charges.
GROUP TRENDS- Atomic radii tend to increase down a group due to the increase in energy levels.
Exceptions- Group 13 Gallium and aluminum. The d block addition causes an increase in the nuclear charge and so a decrease in the atomic radii.

3. - The energy required to remove an electron from a neutral atom. (IE)
FIRST IONIZATION ENERGY
- The energy required to remove an electron from a neutral atom. (IE)
A + energy  A+ + e-
ION- an atom or group of bonded atoms that has a positive or negative charge.
IONIZATION- A process that results in the formation of an ion.

4. Ionization energy continued
PERIOD TRENDS- In general, IE of the main-group elements tends to INCREASE across a period. Again caused by increasing nuclear charge. Group 1-lowest, Group 18-highest.
GROUP TRENDS- In general, IE of the main-group elements tends to DECREASE down a group because the electrons are further from the nucleus.

5. Second, Third (etc) Ionization Energies (IE2 , IE3 , etc)
Each successive removal of an electron requires greater energy because the nucleus has a greater pull on the remaining electrons.
SO…the IE tends to INCREASE across a period.
At noble- gas configuration, the IE takes a huge jump. EX: Be IE2 and IE3 differences.
1757 kJ/mole  kJ/mole

6. ELECTRON AFFINITY The energy change that occurs when an electron is acquired by a neutral atom.
MOST atoms release energy when they acquire an electron
A + e-  A- + energy
Energy released is represented by a negative number in Kj/mole
BUT, some have to be forced to take an electron and so require an input of energy.
A + e- + energy  A-
Energy absorbed is represented by a positive number in Kj/mole

7. ELECTRON AFFINITY continued
PERIOD TRENDS- Affinity becomes MORE NEGATIVE across a period.
Exceptions- Group 14 and 15 because adding an electron to group 14 elements gives a half-full p orbital, while adding an electron to group 15 requires the pairing of electrons in the p sublevel.
GROUP TRENDS- Generally becoming LESS NEGATIVE down a group due to increase in atomic radius, so less pull from the nucleus, even though the pull is a little stronger
Exceptions- heavy transition metals.

8. ELECTRON AFFINITY continued
The addition of a second electron to an already negative ion must always be forced, so second electron affinities are all positive values.

9. IONIC RADII
Cations- Atomic radii tends to DECREASE in positively charged ions.
Anions- Atomic radii tends to INCREASE in negatively charged ions.
PERIOD TRENDS- Cationic radii decrease across a period until group 15 when anions are more common and so an increase in ionic radii is seen.
GROUP TRENDS- Ionic radii tends to INCREASE down a group.

10. VALENCE ELECTRONS
The electrons available to be lost, gained or shared in the formation of chemical compounds.

11. ELECTRONEGATIVITY - the ability of an atom in a compound to attract electrons.
PERIOD TRENDS- Electronegativities tend to increase across a period.
GROUP TRENDS- Electronegativities tend to decrease down a group.
FLOURINE is the MOST ELECTRONEGATIVE element on the table with an electronegativity value of 4.

12. Periodic trends: d- and f- Blocks ATOMIC RADII
PERIOD TRENDS- d- Block
Generally decrease across a period, dip to a low then increase.
PERIOD TRENDS- f-Block
Varies
GROUP TRENDS- d-Block
Generally INCREASE down a group
GROUP TRENDS- f-Block
Generally DECREASE down a group

13. Ionization Energy d- and f- Blocks Generally INCREASE across a period.
Generally INCREASE down a group.

14. ION FORMATION AND IONIC RADII d-Block
The order electrons are removed is exactly the reverse of how they are added in electron-configuration notation.
So… the s orbital electrons are removed first.
Most form 2+ ions
Group 3 forms ONLY 3+ ions
Ionic radii decrease with cation formation.

15. ELECTRONEGATIVITIES
Only Group 1 and 2 have lower electronegativities than d- or f- Block elements
D-Block has higher electronegativities than f-Block generally