Chemical Bonding — Set 2

Correct Answer: D. Electronegativity difference

• **Electronegativity difference** = When atoms have different electronegativities, the electron pair shifts toward the more electronegative atom. • **Partial charges** — The unequal sharing creates δ+ and δ- poles, with larger differences producing more polar bonds. • 💡 Wrong-option analysis: A: Neutrons do not affect bonding; B: Ionization energy determines ease of losing electrons, not bond polarity; C: Atomic mass does not determine polarity.

Correct Answer: C. VSEPR Theory

• **VSEPR theory** = Valence Shell Electron Pair Repulsion theory predicts geometry by minimizing repulsion between electron pairs around the central atom. • **Predicts shapes** — It explains why methane is tetrahedral, water is bent, and ammonia is pyramidal based on electron arrangement. • 💡 Wrong-option analysis: A: Molecular Orbital Theory focuses on orbital combination; B: Dalton's Theory addresses atomic structure; D: Bohr's Theory explains electron energy levels.

Correct Answer: A. High electrical conductivity in molten state

• **Mobile ions conduct** = When melted or dissolved, ions break free from the lattice and move through the liquid to carry electric current. • **Solid insulator** — In solid form, ions are locked in place and cannot move, making ionic compounds insulators. • 💡 Wrong-option analysis: B: Ionic compounds have very high melting points; C: They dissolve in polar solvents like water, not non-polar ones; D: Ionic compounds are crystalline solids at room temperature.

Correct Answer: D. Metallic

• **Electron delocalization** = Metal atoms contribute their valence electrons to a mobile 'sea' that moves freely among the metal cation lattice. • **Explains properties** — This delocalized electron cloud accounts for metallic luster, thermal conductivity, and electrical conductivity. • 💡 Wrong-option analysis: A: Ionic bonding transfers electrons to form fixed ions; B: Covalent bonding localizes electrons between pairs; C: Hydrogen bonding is intermolecular, not a general bonding model.

Correct Answer: D. NH3

• **Ammonia structure** = Nitrogen has one lone pair that repels the three N-H bonding pairs, pushing them into a pyramid-like arrangement. • **107 degrees** — The H-N-H bond angle is compressed from the tetrahedral **109.5°** due to lone pair repulsion being stronger. • 💡 Wrong-option analysis: A: Methane is tetrahedral; B: Carbon dioxide is linear; C: Water is bent, not pyramidal.

Correct Answer: B. Triple bond

• **Triple bond strength** = Three shared electron pairs create extremely high bond energy and short bond length between atoms. • **Bond dissociation energy** — Nitrogen's N≡N triple bond requires **946 kJ/mol** to break, much more than any double or single bond. • 💡 Wrong-option analysis: A: Hydrogen bonds are intermolecular forces, much weaker; C: Double bonds have only 4 electrons; D: Single bonds have only 2 electrons.

Correct Answer: A. Carbon dioxide

• **Symmetrical geometry** = Carbon dioxide's linear arrangement with identical C=O bonds on opposite sides creates equal and opposite dipoles. • **Vector cancellation** — The two bond dipoles point in opposite directions and cancel to give a net dipole moment of zero. • 💡 Wrong-option analysis: B: Ammonia is pyramidal and asymmetrical; C: Water is bent and asymmetrical; D: Hydrogen chloride is linear but has only one bond.

Correct Answer: B. Atomic orbitals

• **Orbital mixing** = Hybridization combines s, p, d orbitals to create new equivalent orbitals oriented toward bonding partners. • **Explains bonding geometry** — sp3 mixing creates four tetrahedra, sp2 creates three planar, and sp creates two linear orbitals. • 💡 Wrong-option analysis: A: Positrons are antiparticles unrelated to bonding; C: Protons are nuclear particles; D: Neutrons are also nuclear particles.

Correct Answer: A. Fluorine

• **Fluorine supremacy** = Fluorine has the highest electronegativity at **3.98** on the Pauling scale due to small atomic size and high nuclear charge. • **Strongest attractions** — Its outer electrons are closest to the nucleus and pulled most strongly from bonded atoms. • 💡 Wrong-option analysis: B: Oxygen is less electronegative than fluorine; C: Cesium is highly electropositive, not electronegative; D: Chlorine is less electronegative than fluorine.

Correct Answer: C. Double covalent bond

• **Oxygen structure** = The O=O double bond consists of one sigma and one pi bond holding two oxygen atoms together. • **Paramagnetism** — Molecular orbital theory shows O2 has unpaired electrons, making it paramagnetic and attracted to magnetic fields. • 💡 Wrong-option analysis: A: Triple bond would have 3 electron pairs; B: Single bond would make it too unreactive; D: Ionic bond requires electron transfer, not sharing.