Periodic Table Trends

1. Atomic Radius

• Trend Across a Period (Left to Right): Decreases because increasing nuclear

charge pulls electrons closer.

• Trend Down a Group (Top to Bottom): Increases due to the addition of

electron shells.

2. Ionization Energy (IE)

• Definition: Energy required to remove an electron from an atom.

• Trend Across a Period: Increases due to stronger nuclear attraction.

• Trend Down a Group: Decreases because outer electrons are farther from

the nucleus and easier to remove.

3. Electronegativity

• Definition: Ability of an atom to attract electrons in a bond.

• Trend Across a Period: Increases (except noble gases) as atoms want to

gain electrons to fill their outer shells.

• Trend Down a Group: Decreases because larger atoms have a weaker pull on

bonding electrons.

• Most Electronegative Element: Fluorine (F).

4. Electron Affinity

• Definition: Energy change when an atom gains an electron.

• Trend Across a Period: Generally increases (becomes more negative)

because atoms want to gain electrons to complete their octet.

• Trend Down a Group: Decreases because larger atoms have a weaker

attraction for additional electrons.

5. Metallic Character

• Definition: How easily an element loses electrons.

• Trend Across a Period: Decreases as elements become more nonmetallic.

• Trend Down a Group: Increases because atoms lose electrons more easily.

6. Reactivity

• Metals: Increase down a group (easier to lose electrons) and decrease

across a period.

• Nonmetals: Decrease down a group and increase across a period (except

noble gases).

7 . Shielding Effect

• Definition: Core electrons block valence electrons from nuclear pull.

• Trend Across a Period: Stays relatively constant.

• Trend Down a Group: Increases due to more electron shells.

8. Effective Nuclear Charge (Z_eff)

• Definition: Net positive charge experienced by valence electrons.

• Trend Across a Period: Increases as protons increase.

• Trend Down a Group: Decreases due to more shielding.

Key Mnemonics to Remember:

• “Bigger as you go down, smaller as you go across” (Atomic Radius).

• “E.N. is FON (Fluorine, Oxygen, Nitrogen)” (Electronegativity).

• “IE follows E.N.” (Higher electronegativity = higher ionization energy).