Periodic Table – Periodic Properties and Variations

ICSE Grade 10 Chemistry - Chapter 1

📚 Smart Summary

1. Modern Periodic Law and Periodic Table

Modern Periodic Law: Properties of elements are periodic functions of their atomic numbers.

Mendeleev's Periodic Law: Properties of elements are periodic functions of their atomic masses (historical).

Modern Periodic Table: Contains 18 groups (vertical columns) and 7 periods (horizontal rows).

Groups: Elements in same group have same number of valence electrons and similar chemical properties.

Periods: Represent the number of electron shells in an atom. Period number = Number of shells.

Classification: Metals (left side), non-metals (right side), metalloids (zigzag line between them).

2. Position of Elements

Group Number: For elements in Groups 1-2 and 13-18, Group number = Number of valence electrons (with modifications).

Period Number: Equals the number of electron shells in the atom.

Electronic Configuration: Determines position. Example: Sodium (2,8,1) → Period 3, Group 1.

Valency: Number of electrons lost, gained, or shared to achieve stable configuration.

Alkali Metals: Group 1 (Li, Na, K, Rb, Cs, Fr). Most reactive metals, valency = 1.

Halogens: Group 17 (F, Cl, Br, I, At). Most reactive non-metals, valency = 1.

Noble Gases: Group 18 (He, Ne, Ar, Kr, Xe, Rn). Inert, valency = 0, stable octet configuration.

3. Periodic Trends - Atomic Size

Atomic Size/Atomic Radius: Distance from nucleus to outermost shell.

Trend Across Period: Decreases from left to right. Nuclear charge increases, pulling electrons closer.

Trend Down Group: Increases from top to bottom. Number of shells increases, outermost electrons farther from nucleus.

Reason: Across period - increased nuclear charge; Down group - increased number of shells.

Example: Na > Mg > Al > Si (decreasing size across period 3).

4. Periodic Trends - Metallic and Non-metallic Character

Metallic Character: Tendency to lose electrons and form positive ions (cations).

Trend Across Period: Decreases from left to right. Elements change from metals to metalloids to non-metals.

Trend Down Group: Increases from top to bottom. Easier to lose electrons as they are farther from nucleus.

Non-metallic Character: Tendency to gain electrons and form negative ions (anions).

Non-metallic Trend: Increases across period (left to right), decreases down group.

Example: In Period 3: Na (metal) → Mg (metal) → Al (metal) → Si (metalloid) → P (non-metal) → S (non-metal) → Cl (non-metal).

5. Periodic Trends - Ionization Energy and Electron Affinity

Ionization Energy (IE): Energy required to remove an electron from gaseous atom. M → M⁺ + e⁻.

IE Trend Across Period: Increases from left to right. Stronger nuclear attraction makes electron removal harder.

IE Trend Down Group: Decreases from top to bottom. Outermost electrons farther from nucleus, easier to remove.

Electron Affinity (EA): Energy released when an electron is added to gaseous atom. M + e⁻ → M⁻.

EA Trend: Generally increases across period, decreases down group (similar to IE but with exceptions).

Noble Gases: Have highest IE and zero/very low EA due to stable electronic configuration.

6. Periodic Trends - Electronegativity and Valency

Electronegativity: Tendency of an atom to attract shared electrons in a covalent bond.

Trend Across Period: Increases from left to right. Fluorine most electronegative element (3.98).

Trend Down Group: Decreases from top to bottom. Distance from nucleus increases.

Valency Variation: For Groups 1-2: valency = group number. For Groups 13-18: valency = 18 - group number (or group number - 10).

Valency Across Period: 1, 2, 3, 4, 3, 2, 1, 0 (for periods 2 and 3).

Example: C (Group 14) has valency 4; O (Group 16) has valency 2; Cl (Group 17) has valency 1.