Metallic Character (Electropositive Nature)

Trend:

• Down a group: ↑ increases
• Across a period (L → R): ↓ decreases

Reason:

• Down the group → atomic size ↑ → valence electrons easily lost
• Across period → effective nuclear charge ↑ → electrons tightly held

✔️ Order Example:

• Group 1: Li < Na < K < Rb < Cs
• Period 3: Na > Mg > Al > Si > P > S > Cl

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Exceptions in Metallic Character

1. Be vs Al

• Normally metallic character ↓ across period
• But: Al > Be (unexpected)

Reason:

• Be has very high ionization energy
• Al can lose electron easily (3p¹ electron is less tightly held)

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2. Ga vs Al

• Expected: Ga > Al (down group)
• Actual: Al > Ga

Reason:

• Poor shielding by d-electrons in Ga → higher effective nuclear charge → harder to lose electron

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Non-Metallic Character (Electronegativity / Electron Gain)

Trend:

• Down a group: ↓ decreases
• Across a period (L → R): ↑ increases

Reason:

• Across period → size ↓, attraction for electrons ↑
• Down group → size ↑, attraction ↓

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✔️ Order Example:

• Group 17: F > Cl > Br > I
• Period 2: Li < Be < B < C < N < O < F

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