Grade: Grade 10 Subject: Science (Chemistry) Unit: Chemical Bonding Lesson: 3 of 6 SAT: ProblemSolving+DataAnalysis ACT: Science

Guided Practice

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This lesson provides step-by-step practice with chemical bonding concepts. Work through each problem to build confidence with Lewis structures, bond types, and molecular properties.

Drawing Lewis Structures - Strategy

  1. Count total valence electrons from all atoms
  2. Draw single bonds between atoms (2 electrons each)
  3. Complete octets on outer atoms first (usually with lone pairs)
  4. Place remaining electrons on central atom
  5. If central atom lacks octet, form multiple bonds

Predicting Bond Type - Strategy

  • Ionic: Metal + Nonmetal (electronegativity difference > 1.7)
  • Polar Covalent: Nonmetal + Nonmetal (EN difference 0.4 - 1.7)
  • Nonpolar Covalent: Same element or very similar EN (< 0.4)

Practice Problems

Problem 1: Draw the Lewis structure for water (H2O).

Solution:

  1. Total valence electrons: O(6) + 2H(1) = 8
  2. Draw O-H bonds (4 electrons used)
  3. Place remaining 4 electrons as 2 lone pairs on O

Answer: O with 2 lone pairs and 2 single bonds to H atoms

Problem 2: Is NaCl ionic or covalent? Explain.

Answer: Ionic

Na is a metal (Group 1) and Cl is a nonmetal (Group 17). Metals transfer electrons to nonmetals, forming ions that attract through electrostatic forces.

Problem 3: Draw the Lewis structure for CO2.

Solution:

  1. Total valence electrons: C(4) + 2O(6) = 16
  2. C is central atom
  3. Single bonds would give C only 4 electrons
  4. Form double bonds: O=C=O
  5. Each O has 2 lone pairs

Answer: O=C=O with 2 lone pairs on each oxygen

Problem 4: Predict whether the bond in HCl is polar or nonpolar covalent.

Answer: Polar covalent

Both H and Cl are nonmetals, so the bond is covalent. Cl is more electronegative than H, so electrons are unequally shared, making it polar.

Problem 5: Draw the Lewis structure for ammonia (NH3).

Solution:

  1. Total valence electrons: N(5) + 3H(1) = 8
  2. N is central, bonded to 3 H atoms (6 electrons)
  3. Remaining 2 electrons form a lone pair on N

Answer: N with 1 lone pair and 3 single bonds to H atoms

Problem 6: What type of bond forms between two oxygen atoms in O2?

Answer: Nonpolar covalent (double bond)

Same atoms have identical electronegativity, so electrons are shared equally.

Problem 7: Draw the Lewis structure for methane (CH4).

Solution:

  1. Total valence electrons: C(4) + 4H(1) = 8
  2. C is central with 4 single bonds to H
  3. All electrons used, C has octet

Answer: C with 4 single bonds to H atoms (no lone pairs)

Problem 8: Predict the type of bonding in MgO.

Answer: Ionic

Mg is a metal (Group 2) that loses 2 electrons to form Mg2+. O is a nonmetal (Group 16) that gains 2 electrons to form O2-. The ions attract electrostatically.

Problem 9: Draw the Lewis structure for nitrogen gas (N2).

Solution:

  1. Total valence electrons: 2N(5) = 10
  2. Triple bond between N atoms (6 electrons)
  3. Each N has 1 lone pair (4 electrons)

Answer: N triple bond N, each with 1 lone pair

Problem 10: Is the C-O bond in CO2 polar or nonpolar? Is the molecule polar or nonpolar?

Answer:

Each C-O bond is polar (O is more electronegative than C).

However, CO2 is a nonpolar molecule because it's linear and the polar bonds cancel out (symmetric arrangement).

Check Your Understanding

  1. What determines whether a bond is ionic or covalent?
  2. How do you know when to draw multiple bonds in a Lewis structure?
  3. What's the difference between a polar bond and a polar molecule?

Next Steps

  • If you scored 8-10 correct, move on to Polarity and Properties
  • If you scored below 8, review the examples and try again