1Valence e⁻ & Lewis
How many valence electrons does NOCl have in total?
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A) 18. N 5 + O 6 + Cl 7 = 18.
Answer: A) 18. N 5 + O 6 + Cl 7 = 18.
30 multiple-choice + 2 free-response = 32 questions · electron domains · electron & molecular geometry · bond angles · 3-D drawings · bond & molecular polarity
How many valence electrons does NOCl have in total?
A) 18. N 5 + O 6 + Cl 7 = 18.
Answer: A) 18. N 5 + O 6 + Cl 7 = 18.
How many valence electrons does CF₂Cl₂ have in total?
D) 32. C 4 + F 2 × 7 + Cl 2 × 7 = 32.
Answer: D) 32. C 4 + F 2 × 7 + Cl 2 × 7 = 32.
In the Lewis structure of the nitrite ion, NO₂⁻, how many lone pairs sit on the N atom?
C) 1. 18 e⁻: the skeleton O–N–O uses 4, 12 go on the O atoms, and the last 2 are one lone pair on N. After the N=O double bond forms, N has 2 bonds + 1 lone pair.
Answer: C) 1. 18 e⁻: the skeleton O–N–O uses 4, 12 go on the O atoms, and the last 2 are one lone pair on N. After the N=O double bond forms, N has 2 bonds + 1 lone pair.
How many electron domains are around C in the formate ion, HCO₂⁻?
B) 3. C is bonded to H and two O and has no lone pair. The C=O double bond counts as one domain, so there are 3.
Answer: B) 3. C is bonded to H and two O and has no lone pair. The C=O double bond counts as one domain, so there are 3.
Which of these counts as exactly ONE electron domain on the central atom?
A) A double bond to an outer atom. Any bond (single, double or triple) to one atom is one domain (NCERT: a multiple bond is treated as a single "super pair"). Outer-atom lone pairs and the charge are not domains.
Answer: A) A double bond to an outer atom. Any bond (single, double or triple) to one atom is one domain (NCERT: a multiple bond is treated as a single "super pair"). Outer-atom lone pairs and the charge are not domains.
What is the ELECTRON geometry of PBr₃?
D) Tetrahedral. P has 3 bonded Br + 1 lone pair = 4 domains, so the electron geometry is tetrahedral. (Trigonal pyramidal is its molecular geometry.)
Answer: D) Tetrahedral. P has 3 bonded Br + 1 lone pair = 4 domains, so the electron geometry is tetrahedral. (Trigonal pyramidal is its molecular geometry.)
What is the electron geometry of NOCl?
C) Trigonal planar. N has 2 bonded atoms + 1 lone pair = 3 domains, so it is trigonal planar.
Answer: C) Trigonal planar. N has 2 bonded atoms + 1 lone pair = 3 domains, so it is trigonal planar.
What is the ideal angle between four electron domains?
B) 109.5°. Four domains point to the corners of a tetrahedron: cos θ = −1/3, so θ = 109.5°.
Answer: B) 109.5°. Four domains point to the corners of a tetrahedron: cos θ = −1/3, so θ = 109.5°.
The electron geometry and the molecular geometry have the same name when…
A) the central atom has no lone pairs. The molecular geometry leaves out the lone pairs, so the names match only when there are no lone pairs on the central atom.
Answer: A) the central atom has no lone pairs. The molecular geometry leaves out the lone pairs, so the names match only when there are no lone pairs on the central atom.
What is the molecular geometry of NO₂⁻?
D) Bent. 3 domains (2 atoms + 1 lone pair), so the electron geometry is trigonal planar and the shape is bent.
Answer: D) Bent. 3 domains (2 atoms + 1 lone pair), so the electron geometry is trigonal planar and the shape is bent.
What is the molecular geometry of CF₂Cl₂?
C) Tetrahedral. 4 bonded atoms and no lone pair on C gives tetrahedral. The outer atoms being different does not change the shape.
Answer: C) Tetrahedral. 4 bonded atoms and no lone pair on C gives tetrahedral. The outer atoms being different does not change the shape.
What is the molecular geometry of the hydronium ion, H₃O⁺?
B) Trigonal pyramidal. 8 e⁻: O has 3 bonds + 1 lone pair = 4 domains, so the shape is trigonal pyramidal (like NH₃).
Answer: B) Trigonal pyramidal. 8 e⁻: O has 3 bonds + 1 lone pair = 4 domains, so the shape is trigonal pyramidal (like NH₃).
SO₃ is trigonal planar, but the sulfite ion SO₃²⁻ is trigonal pyramidal. Why?
A) The 2 extra electrons form a lone pair on S. SO₃ has 24 e⁻ (3 domains on S). SO₃²⁻ has 26 e⁻: the extra 2 become a lone pair on S, giving 4 domains, 3 atoms and a trigonal pyramidal shape.
Answer: A) The 2 extra electrons form a lone pair on S. SO₃ has 24 e⁻ (3 domains on S). SO₃²⁻ has 26 e⁻: the extra 2 become a lone pair on S, giving 4 domains, 3 atoms and a trigonal pyramidal shape.
What is the O–N–Cl bond angle in NOCl?
D) Slightly less than 120°. A trigonal planar electron geometry with 1 lone pair: the lone pair squeezes the bond angle a little below 120° (about 113°).
Answer: D) Slightly less than 120°. A trigonal planar electron geometry with 1 lone pair: the lone pair squeezes the bond angle a little below 120° (about 113°).
Which molecule has the SMALLEST bond angle?
C) H₂O. H₂O 104.5° < NH₃ 107° < CH₄ 109.5° < BF₃ 120°. Two lone pairs squeeze the most (NCERT Table 4.8).
Answer: C) H₂O. H₂O 104.5° < NH₃ 107° < CH₄ 109.5° < BF₃ 120°. Two lone pairs squeeze the most (NCERT Table 4.8).
Which is the correct order of repulsion strength?
B) lone pair–lone pair > lone pair–bond pair > bond pair–bond pair. NCERT §4.4. Lone pairs are held by one nucleus only, spread out more and push harder.
Answer: B) lone pair–lone pair > lone pair–bond pair > bond pair–bond pair. NCERT §4.4. Lone pairs are held by one nucleus only, spread out more and push harder.
Which of these is LINEAR?
A) HCN. HCN: C has 2 domains (C–H and C≡N) and no lone pair, so it is linear. The other three are bent.
Answer: A) HCN. HCN: C has 2 domains (C–H and C≡N) and no lone pair, so it is linear. The other three are bent.
A central atom has 2 bonded atoms and 2 lone pairs. What is the shape?
D) Bent, about 104.5°. 4 domains give a tetrahedral electron geometry. With 2 lone pairs, the atoms form a bent shape at about 104.5°, like H₂O.
Answer: D) Bent, about 104.5°. 4 domains give a tetrahedral electron geometry. With 2 lone pairs, the atoms form a bent shape at about 104.5°, like H₂O.
In a wedge-and-dash drawing, a hashed wedge (dash) means the bond…
C) points back, away from you. Plain line: in the plane. Solid wedge: toward you. Hashed wedge: away from you.
Answer: C) points back, away from you. Plain line: in the plane. Solid wedge: toward you. Hashed wedge: away from you.
Which is the correct 3-D drawing of NH₃?
B. NH₃ has 4 domains (3 H + 1 lone pair), so it is trigonal pyramidal: the lone pair on top, with 1 plain line, 1 wedge and 1 dash below.
Answer: B. NH₃ has 4 domains (3 H + 1 lone pair), so it is trigonal pyramidal: the lone pair on top, with 1 plain line, 1 wedge and 1 dash below.
Which drawing shows the shape of CF₂Cl₂ (X = F or Cl)?
A. Four bonded atoms and no lone pair on C: tetrahedral, with 2 bonds in the plane, 1 wedge and 1 dash.
Answer: A. Four bonded atoms and no lone pair on C: tetrahedral, with 2 bonds in the plane, 1 wedge and 1 dash.
Using NCERT electronegativities, which bond is NONPOLAR?
D) C–H. C–H: 2.5 − 2.1 = 0.4, below 0.5. The others: C–O 1.0, P–Br 0.7, C–F 1.5, all polar.
Answer: D) C–H. C–H: 2.5 − 2.1 = 0.4, below 0.5. The others: C–O 1.0, P–Br 0.7, C–F 1.5, all polar.
What is ΔEN for a C–F bond, and what kind of bond is it?
C) 1.5, polar covalent. 4.0 − 2.5 = 1.5, which is between 0.5 and 1.7, so it is polar covalent.
Answer: C) 1.5, polar covalent. 4.0 − 2.5 = 1.5, which is between 0.5 and 1.7, so it is polar covalent.
In the crossed-arrow dipole for an H–Cl bond, the arrowhead points toward…
B) Cl, the more electronegative atom. The cross sits at the δ+ end (H) and the arrowhead at the δ− end (Cl), which is where the electrons are pulled (NCERT §4.3.6).
Answer: B) Cl, the more electronegative atom. The cross sits at the δ+ end (H) and the arrowhead at the δ− end (Cl), which is where the electrons are pulled (NCERT §4.3.6).
Which bond in NOCl is nonpolar (NCERT values)?
A) N–Cl. N–Cl: 3.0 − 3.0 = 0, nonpolar. N=O: 3.5 − 3.0 = 0.5, polar.
Answer: A) N–Cl. N–Cl: 3.0 − 3.0 = 0, nonpolar. N=O: 3.5 − 3.0 = 0.5, polar.
Which molecule is NONPOLAR?
D) CO₂. CO₂ is linear, so its two equal C=O dipoles cancel (0 D). The others are bent or pyramidal.
Answer: D) CO₂. CO₂ is linear, so its two equal C=O dipoles cancel (0 D). The others are bent or pyramidal.
CCl₄ has four polar C–Cl bonds. Why is the molecule nonpolar?
C) It is tetrahedral with 4 identical atoms, so the dipoles cancel. Four equal vectors to the corners of a tetrahedron add to zero (NCERT Table 4.5: CCl₄ = 0 D).
Answer: C) It is tetrahedral with 4 identical atoms, so the dipoles cancel. Four equal vectors to the corners of a tetrahedron add to zero (NCERT Table 4.5: CCl₄ = 0 D).
Which of these is POLAR?
B) CF₂Cl₂. CF₂Cl₂ is tetrahedral, but the C–F dipoles (1.5) are stronger than the C–Cl dipoles (0.5), so they can't cancel.
Answer: B) CF₂Cl₂. CF₂Cl₂ is tetrahedral, but the C–F dipoles (1.5) are stronger than the C–Cl dipoles (0.5), so they can't cancel.
The formate ion, HCO₂⁻, is trigonal planar. Is it polar?
A) Yes: the outer atoms are not all the same (H vs O). A symmetric shape cancels only if all the outer atoms are identical. The strong C–O dipoles are not balanced by the weak C–H.
Answer: A) Yes: the outer atoms are not all the same (H vs O). A symmetric shape cancels only if all the outer atoms are identical. The strong C–O dipoles are not balanced by the weak C–H.
NCERT lists H₂O at 1.85 D but CO₂ at 0 D, though both have polar bonds. What explains the difference?
D) H₂O is bent, CO₂ is linear. The shape decides it. The bent H₂O's dipoles add (2µ cos 52.25°), while the linear CO₂'s point in opposite directions and cancel.
Answer: D) H₂O is bent, CO₂ is linear. The shape decides it. The bent H₂O's dipoles add (2µ cos 52.25°), while the linear CO₂'s point in opposite directions and cancel.
Complete every column of the worksheet row for SO₂: valence e⁻, Lewis structure, electron geometry, molecular geometry & bond angle, the 3-D redraw, bond polarity and molecular polarity.
Complete the row for CHCl₃, then explain in one or two sentences why CHCl₃ is polar while CCl₄ is not.