1. Periodic Trends

2. MN Standards
Students know how to use the periodic table to identify trends in ionization energy, electronegativity, and the relative sizes of ions and atoms.

3. Trends in Atomic Size
First problem: Where do you start measuring from?
The electron cloud doesn’t have a definite edge.
They get around this by measuring more than 1 atom at a time.

4. Period Trend: Atomic Radius

5. Atomic Radius
Definition: Half of the distance between nuclei in covalently bonded diatomic molecule
Radius decreases across a period
Increased effective nuclear charge due to decreased shielding
Radius increases down a group
Each row on the periodic table adds a “shell” or energy level to the atom

6. Influenced by three factors: 1. Energy Level
Trends in Atomic Size
Influenced by three factors:
1. Energy Level
Higher energy level is further away.
2. Charge on nucleus
More charge pulls electrons in closer.
3. Shielding effect:
e <-> e repulsion

7. Table of Atomic Radii

9. Periodic Trend: Ionization Energy

10. Ionization Energy
Definition: the energy required to remove an electron from an atom
Tends to increase across a period
As radius decreases across a period, the electron you are removing is closer to the nucleus and harder to remove
Tends to decrease down a group
Outer electrons are farther from the nucleus and easier to remove

11. Periodic Trend: Electronegativity

12. Electronegativity
Definition: A measure of the ability of an atom in a chemical compound to attract electrons
Electronegativity tends to increase across a period
As radius decreases, electrons get closer to the bonding atom’s nucleus
Electronegativity tends to decrease down a group or remain the same
As radius increases, electrons are farther from the bonding atom’s nucleus

13. Periodic Table of Electronegativities

14. Summary of Periodic Trends

15. Ionic Radii Cations Anions Positively charged ions formed when
an atom of a metal loses one or
more electrons
Cations
Smaller than the corresponding
atom
Negatively charged ions formed
when nonmetallic atoms gain one
or more electrons
Anions
Larger than the corresponding
atom

16. Graphic courtesy Wikimedia Commons user Popnose

17. p.190, figure 6.14
Ionic size decreases
Ionic size increases