1. Trends of the Periodic Table
Representative elements (main group) only—so, transition and inner transition metals are not included in the trends
Group/family: column of periodic table
Period: row of the periodic table

2. Atomic Radius: (atoms without charge) ½ the distance across atom
Decreases left to right (across a period) because of the pull from the nucleus as the outer energy level fills
Increase top to bottom (down a group) because of the additional energy level

3. Atomic Radius…examples
What’s bigger?
sodium or chlorine?
hydrogen or potassium?
What’s smaller?
potassium or nickel?
fluorine or bromine?

4. Ionization Energy: The energy required to remove the valence electron from an atom
Increases left to right (across period) because the electron is closer to the nucleus
Decrease going down a group because the electron is further from the nucleus

5. Ionization Energy…examples
Which has a greater ionization energy?
sodium or chlorine?
hydrogen or potassium?
Which has a smaller ionization energy?
potassium or nickel?
fluorine or bromine?

6. Electronegativity increases across a period
Electronegativity: The ability of an atom to attract electrons in a chemical bond
Electronegativity increases across a period
Electronegativity decreases down a group H
2.1 Li
1.0 Be
1.5 B
2.0 C
2.5 N
3.0 O
3.5 F
4.0 Na
0.9 Mg
1.2 Al Si
1.8 P S Cl K
0.8 Ca Ga
1.6 Ge As Se
2.4 Br
2.8 Rb Sr In
1.7 Sn Sb
1.9 Te I Cs
0.7 Ba Tl Pb Bi

7. Electronegativity…examples
Which has a greater electronegativity?
sodium or chlorine?
hydrogen or potassium?
Which has a smaller electronegativity?
potassium or nickel?
fluorine or bromine?