Topic 3: Chemical Bonding Flashcards
Definitions I:
(a) Electronegativity
(b) Ionic bonding
(c) Covalent bonding
Definitions I:
(a) Power of an atom in a molecule to attract electrons to itself.
(b) Electrostatic attraction between oppositely charged ions (cations and anions).
(c) Electrostatic attraction between two nuclei and a shared pair of electrons.
Definitions II:
(a) Metallic bonding
(b) Coordinate bonding
(c) Bond energy
Definitions II:
(a) Electrostatic attraction between positive metal ions and delocalised electrons.
(b) Covalent bond where one atom donates both electrons, e.g., NH₄⁺.
(c) Energy required to break one mole of a covalent bond in gaseous state.
Definitions III:
(a) Bond length
(b) Hydrogen bonding
(c) Van der Waals’ forces
Definitions III:
(a) Internuclear distance between two covalently bonded atoms.
(b) Strong attraction between N-H, O-H, or F-H & lone pair on N/O/F.
(c) Intermolecular forces between molecules, including London and dipole forces.
Predict the bond type using electronegativity differences for:
(a) NaCl (3.0) [1 Mark]
(b) HCl (0.9) [1 Mark]
(a) Difference 2.1 > 1.7, ionic (1 mark)
(b) Difference 0.9 < 1.7, polar covalent (1 mark)
What factors affect electronegativity, and how does it trend across Period 3? [2 Marks]
Nuclear charge increases, radius decreases, shielding similar across Period 3 (1 mark)
More attraction to electrons, electronegativity increases (1 mark)
What are the shapes and bond angles of:
(a) NH₃? [1 Mark]
(b) SF₆? [1 Mark]
(a) Pyramidal, 107° (1 mark)
(b) Octahedral, 90° (1 mark)
Describe σ and π bonds in:
(a) C₂H₄ [1 Mark]
(b) N₂ [1 Mark]
(a) One σ (sp² overlap), one π (p overlap) (1 mark)
(b) One σ (sp overlap), two π (p overlap) (1 mark)
How does hydrogen bonding affect the boiling point and density of H₂O? [3 Marks]
Strong H-bonds increase boiling point (1 mark)
Open structure in ice lowers density (1 mark)
Compared to weaker forces in similar molecules (1 mark)
What is the dot-and-cross diagram for:
(a) NaCl? [1 Mark]
(b) NH₄⁺? [1 Mark]
(a) Na⁺ [2,8]⁺ Cl⁻ [2,8,8]⁻, dots/crosses show transfer (1 mark)
(b) NH₄⁺, N shares 3, H⁺ accepts 1 dative (1 mark)
Why does CH₄ have a lower boiling point than H₂O? [2 Marks]
H₂O has hydrogen bonding, CH₄ only has weak van der Waals’ (1 mark)
Stronger forces in H₂O raise boiling point (1 mark)
How do bond energy and length affect reactivity of Cl₂ vs. Br₂? [2 Marks]
Cl₂ bond energy higher (243 kJ/mol), length shorter (199 pm) (1 mark)
Br₂ less reactive, weaker bond (193 kJ/mol), longer (228 pm) (1 mark)
Describe metallic bonding in copper and its effect on conductivity [2 Marks]
Positive Cu ions in lattice, delocalised electrons (1 mark)
Electrons move, high conductivity (1 mark)
Molecular Shapes
Molecular Shapes:
Little → Linear, 180°
Pigs → Planar (Trigonal), 120°
Buy → Bipyramidal (Trigonal), 90°/120°
Tasty → Tetrahedral, 109.5°
Treats → Trigonal Pyramidal, ~107°
Before → Bent, ~104.5°
Octopuses → Octahedral, 90°
