Questions covering electron gain enthalpy, electronegativity, and valency to help students understand how atoms gain, share, or lose electrons in chemical reactions.
Hydrogen bonding strength depends on electronegativity and size. F (in HF) forms the strongest hydrogen bonds due to its high electronegativity (4.0) and small size, unlike Cl, Br, or I.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Electron Gain Enthalpy and Electronegativity and Valency
Group 15 elements form acidic oxides, especially higher oxides. P forms P₂O₅, which is acidic, unlike Be (basic), Ca (basic), or Zn (amphoteric).
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Electron Gain Enthalpy and Electronegativity and Valency
Electron gain enthalpy becomes more negative across a period and less negative down a group. In group 16, O (period 2) has the most negative value compared to S, Se, and Te.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Electron Gain Enthalpy and Electronegativity and Valency
Electron affinity is the energy change for X + e⁻ -> X⁻. Cl has the highest electron affinity due to its balance of size and nuclear charge, though F’s electron gain enthalpy is less negative due to repulsion.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Electron Gain Enthalpy and Electronegativity and Valency
Al (group 13, valence 3) and O (group 16, valence 2) form Al₂O₃ by cross-multiplying valences.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Electron Gain Enthalpy and Electronegativity and Valency
In period 2, the largest electronegativity difference is between Li (1.0) and F (4.0), a gap of 3.0, compared to other pairs like Be-B or C-N.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Electron Gain Enthalpy and Electronegativity and Valency
In period 5 d-block (Y to Cd), melting point peaks with strong metallic bonding. Mo (group 6, 4d⁵ 5s¹) has the highest melting point due to maximum unpaired electrons.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Electron Gain Enthalpy and Electronegativity and Valency
Electron gain enthalpy becomes less negative down group 17 due to increasing size. Order: Cl (most negative) > F > Br.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Electron Gain Enthalpy and Electronegativity and Valency
Smaller size and higher electronegativity favor pi-bonding in group 14. C (period 2) forms pi-bonds (e.g., in C₂H₄) more readily than Si, Ge, or Sn due to effective 2p orbital overlap.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Electron Gain Enthalpy and Electronegativity and Valency
For isoelectronic species (K+, Ca²⁺, Sc³⁺, all with 18 electrons), radius decreases with increasing nuclear charge. Sc³⁺ (Z=21) has the smallest radius.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Electron Gain Enthalpy and Electronegativity and Valency
Electronegativity decreases down a group due to increasing size. For group 16: O > S > Se.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Electron Gain Enthalpy and Electronegativity and Valency
In period 5 d-block (Y to Cd), melting point peaks with strong metallic bonding due to maximum unpaired electrons. Mo (group 6, 4d⁵ 5s¹) has the highest melting point.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Electron Gain Enthalpy and Electronegativity and Valency
