1. The Diatomics They are elements that are found as two atoms bonded to themselves. They are H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2 There are 7 of them and they are located here:

2. Even More About the Periodic Table Periodic Trends

3.  Atomic radius - one-half the distance between the nuclei of two atoms of the same element when the atoms are joined  In general, atomic size increases from top to bottom within a group and decreases from left to right across a period. Trends in Atomic Size

4. Periodic Trends Notes

5.  Cations are always smaller than the atoms from which they form.  Anions are always larger than the atoms from which they form. Trend in Ionic Size

6. Periodic Trends Notes

7.  First ionization energy tends to decrease from top to bottom within a group and increase from left to right across a period. Trends in Ionization Energy

8.  In general, electronegativity values decrease from top to bottom within a group. For representative elements, the values tend to increase from left to right across a period. Trends in Electronegativity

10.  The trends that exist among these properties can be explained by variations in atomic structure.  The increase in nuclear charge within groups and across periods explains many trends.  Within groups an increase in shielding (distance from the nucleus) has a significant effect Summary of Trends

11. 1 2 18 17 1615 14 13 Atomic size DECREASES Ionization energy INCREASES Electronegativity INCREASES Nuclear charge INCREASES Shielding is constant Atomic size INCREASES Ionization energy DECREASES Electronegativity DECREASES Nuclear charge INCREASES Shielding INCREASES Ionic size INCREASES Size of cations decreases Size of anions decreases

12. Periodic Trends Notes