Periodic Table (Trends and Groups)

📘 THE PERIODIC TABLE (TRENDS & GROUPS)

The Periodic Table arranges all known elements in order of increasing atomic number (proton number).
Elements with similar properties fall into the same group (vertical column).

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1️⃣ Structure of the Periodic Table

• Groups: Vertical columns (1–18)

• Periods: Horizontal rows (1–7)

• Metals are on the left, non-metals on the right.

• Metalloids lie along the zig-zag line.

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2️⃣ Periodic Trends (Across a Period → Left to Right)

🔹 1. Atomic Radius Decreases

• Why? More protons = stronger attraction pulling electrons closer.

🔹 2. Ionization Energy Increases

(IE = energy needed to remove an electron)

• Because atoms get smaller → electrons held more tightly.

🔹 3. Electron Affinity Becomes More Negative

• Atoms want electrons more strongly as you move right.

🔹 4. Electronegativity Increases

• Non-metals strongly attract electrons for bonding.

🔹 5. Metallic Character Decreases

• Metals on the left → non-metals on the right.

🔹 6. Reactivity

• Metals become less reactive.

• Non-metals (especially halogens) become more reactive.

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3️⃣ Group Trends (Down a Group → Top to Bottom)

🔹 1. Atomic Radius Increases

• More shells are added = bigger atoms.

🔹 2. Ionization Energy Decreases

• Outer electrons are farther → easier to remove.

🔹 3. Electronegativity Decreases

• Larger atoms attract electrons less strongly.

🔹 4. Metallic Character Increases

• Elements become more metallic down the group.

🔹 5. Reactivity

• Group 1 metals: Reactivity increases down the group.

• Group 17 non-metals: Reactivity decreases down the group.

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4️⃣ Important Groups You MUST Know

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⭐ GROUP 1 — ALKALI METALS

Examples: Li, Na, K, Rb, Cs

• Very reactive

• Soft metals

• Form +1 ions

• React vigorously with water

• Reactivity increases down the group

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⭐ GROUP 2 — ALKALINE EARTH METALS

Examples: Be, Mg, Ca, Sr, Ba

• Less reactive than Group 1

• Form +2 ions

• Harder metals

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⭐ GROUP 7 / 17 — HALOGENS

Examples: F, Cl, Br, I

• Very reactive non-metals

• Form –1 ions

• Poor conductors

• Reactivity decreases down the group

• Form salts with metals (e.g., NaCl)

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⭐ GROUP 0 / 18 — NOBLE GASES

Examples: He, Ne, Ar, Kr, Xe

• Very unreactive (inert)

• Stable electronic configuration

• Monoatomic gases

• Used in bulbs, lasers, and welding

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5️⃣ Periodicity

Periodicity simply means the repeating pattern of chemical and physical properties across periods and groups due to the arrangement of electrons.

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6️⃣ Likely WAEC/JAMB Questions

1. State two trends across a period.

2. Explain why ionization energy increases across a period.

3. What happens to atomic radius down a group?

4. Compare reactivity trends in Group 1 and Group 17.

5. Name three noble gases and give one property.