1. Periodic Trends

2. Electronegativity
a measure of the ability of an atom in a chemical compound to attract electrons
Trends
Electronegativities tend to increase across each period.
Electronegativities tend to decrease down a group.

3. Electronegativity
Among the elements Ga, Br, Ca, which has the highest electronegativity? Explain why in terms of periodic trends.
All elements in 4th period. Br has highest atomic number and is farthest to right so you would expect highest EN.

4. Electron Affinity
the energy change that occurs when an electron is acquired by a neutral atom
Trends
Electron affinity increases across period because as electrons add to the same p sublevel of atoms with increasing nuclear charge, electron affinities become more negative across each period in the p block.
Generally, electrons add with greater difficulty down a group. This is due to slight increase in effective nuclear charge down a group which decreases the electron affinities.

5. Ionization Energy
the energy required to remove one electron from a neutral atom of an element
Trends
Ionization energy of main group elements generally increases across each period. This is caused by an increasing nuclear charge.
Ionization energy generally decreases down groups because electrons are farther from the nucleus and are more easily removed

6. Ionic Radii
A positive ion is a cation. The removal of an electron makes the radius smaller.
A negative ion is an anion. The addition of an electron makes the radius larger.

7. Atomic Radius
one-half the distance between the nuclei of identical atoms that are bonded together
Trends
Atomic radius decreases across a period because of the increasing positive charge of the nucleus.
Atomic radius increases down a group because electrons occupy successively higher main energy levels which are located farther from the nucleus.
Period—as electrons add to s and p sublevels in the same energy level, they are gradually pulled closer to the more highly charged nucleus.. Increased pull results in decrease in atomic radii

8. Atomic Radius
Of the elements Mg, Cl, Na, and P, which has the largest atomic radius? Explain your answer in terms of trends.
Of the elements Ca, Be, Ba, and Sr, which has the largest atomic radius? Explain your answer in terms of trends.
Of the elements Li, O, C, and F, identify one with the largest atomic radius and the one with the smallest atomic radius.
Of the elements Br, At, F, I, and Cl, identify one with the largest atomic radius and the one with the smallest atomic radius.
1.All elements in period 3. Na has lowest atomic number. AR decrease across a period.
Ba has the highest atomic number and is farthest down the group. AR increases down a group
Largest: Li Smallest F Largest: At Smallest F