Bonding, Formulas & Molecular Structure — Chapter quiz · Physical Science: Chemistry, Grade 11

Build names, formulas, Lewis structures, and structure-property explanations.

Problem 1

A positively charged ion formed when an atom loses electrons is called a…
  1. molecule
  2. isotope
  3. anion
  4. cation
Answer and explanation

cation

Losing electrons leaves more protons than electrons, giving a positive cation.

Problem 2

Magnesium (Mg²⁺) combines with chloride (Cl⁻) ions. How many chloride ions are needed for each magnesium ion?
Answer and explanation

2

Each Cl⁻ is −1, so two are needed to balance the +2 of Mg²⁺, giving MgCl₂.

Problem 3

Which property is typical of ionic compounds?
  1. conducts electricity as a solid
  2. high melting point and brittle
  3. made of discrete molecules
  4. a very low melting point
Answer and explanation

high melting point and brittle

Strong lattice-wide attractions give ionic compounds high melting points and make them hard but brittle.

Problem 4

Aluminum (Al³⁺) reacts with oxygen (O²⁻) to form aluminum oxide. How many atoms in total (aluminum plus oxygen) are in one formula unit?
Answer and explanation

5

Balancing charges gives Al₂O₃, so 2 aluminum + 3 oxygen = 5 atoms.

Problem 5

A covalent bond forms when atoms…
  1. share electrons
  2. form ions
  3. release protons
  4. transfer electrons
Answer and explanation

share electrons

Covalent bonding is the sharing of electron pairs between atoms.

Problem 6

How many electrons are shared in a double bond?
Answer and explanation

4

A double bond is 2 shared pairs, and 2 pairs × 2 electrons = 4 electrons.

Problem 7

The 'sea of electrons' in a metal is made of…
  1. neutrons
  2. delocalized valence electrons
  3. anions
  4. protons
Answer and explanation

delocalized valence electrons

Metallic bonding features valence electrons that are delocalized and free to move throughout the metal.

Problem 8

Which metallic property is explained by layers of ions sliding while the electron sea keeps holding them together?
  1. brittleness
  2. luster
  3. malleability
  4. high density
Answer and explanation

malleability

Malleability comes from ion layers sliding without breaking, because the mobile electron sea keeps them bonded.

Problem 9

Explain why molten (liquid) sodium chloride conducts electricity but solid sodium chloride does not, while solid copper conducts electricity either way.
Answer and explanation

In solid NaCl the ions are locked in a rigid lattice and can't move, so there are no free charges; melting frees the ions to move, so molten NaCl conducts. In copper, a metal, the valence electrons are delocalized in an electron sea and are free to move even in the solid, so solid copper conducts.

Problem 10

According to VSEPR theory, the electron groups around a central atom…
  1. stay locked at 90° angles
  2. disappear once a bond forms
  3. attract one another
  4. repel and spread as far apart as possible
Answer and explanation

repel and spread as far apart as possible

Electron groups repel and spread out as far as possible, which fixes the molecule's shape.

Problem 11

A methane molecule (CH₄), with four bonding pairs and no lone pairs, has which shape?
  1. tetrahedral
  2. trigonal planar
  3. linear
  4. bent
Answer and explanation

tetrahedral

Four electron groups point to the corners of a tetrahedron, giving a tetrahedral shape (~109.5°).

Problem 12

Carbon dioxide (CO₂) has two polar bonds but is a nonpolar molecule because…
  1. it has lone pairs on the carbon atom
  2. it has no electronegativity difference in its bonds
  3. its linear, symmetric shape makes the bond dipoles cancel
  4. it is actually an ionic compound
Answer and explanation

its linear, symmetric shape makes the bond dipoles cancel

The molecule is linear and symmetric, so its two equal bond dipoles point in opposite directions and cancel.

Problem 13

Explain the following claim and supply a valid example or counterexample: Ionic solids are extended lattices, not isolated little NaCl molecules.
Answer and explanation

Ca²⁺ needs two Cl⁻ ions for neutrality; a 1:1 formula would carry +1 net charge. Ionic solids are extended lattices, not isolated little NaCl molecules.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 14

Independent chapter check: Al³⁺ combines with O²⁻. Find the simplest neutral formula and explain why it is not a five-ion molecule drawing for the solid.
Answer and explanation

The least common charge magnitude is 6: two Al³⁺ and three O²⁻ give +6−6=0, so Al₂O₃. The formula states a stoichiometric ratio in an extended solid, not a claim of isolated five-ion molecules.

The least common charge magnitude is 6: two Al³⁺ and three O²⁻ give +6−6=0, so Al₂O₃. The formula states a stoichiometric ratio in an extended solid, not a claim of isolated five-ion molecules.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 15

Explain the following claim and supply a valid example or counterexample: Sharing need not be equal; polar covalent bonds share electron density unevenly.
Answer and explanation

Three shared pairs give six bonding electrons, not three. Sharing need not be equal; polar covalent bonds share electron density unevenly.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 16

Independent chapter check: Compare CO₂ and H₂O: both have polar bonds. Explain why bond polarity alone cannot establish that both molecules have a net dipole.
Answer and explanation

CO₂ is linear with equal opposing bond contributions that cancel in the ideal symmetric molecule. H₂O is bent, so its bond dipoles do not cancel. Geometry and the full charge distribution matter.

CO₂ is linear with equal opposing bond contributions that cancel in the ideal symmetric molecule. H₂O is bent, so its bond dipoles do not cancel. Geometry and the full charge distribution matter.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 17

Explain the following claim and supply a valid example or counterexample: Not all metals have the same melting point or strength; electron-sea pictures are simplified.
Answer and explanation

Copper has delocalized mobile electrons; salt’s ions are fixed in a lattice under ordinary conditions. Not all metals have the same melting point or strength; electron-sea pictures are simplified.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 18

Independent chapter check: A part requires strength index ≥60 and conduction index ≥70. Materials P, Q and R score (65,80), (90,50), and (50,95). Select a feasible option and name a missing design consideration.
Answer and explanation

P satisfies both stated constraints. Q fails conduction and R fails strength. Cost, corrosion, fatigue, fabrication or service temperature could still change the decision.

P satisfies both stated constraints. Q fails conduction and R fails strength. Cost, corrosion, fatigue, fabrication or service temperature could still change the decision.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 19

Explain the following claim and supply a valid example or counterexample: Polar bonds do not automatically make a polar molecule.
Answer and explanation

CO₂ is linear with equal opposite bond dipoles that cancel; bent water has a nonzero molecular dipole. Polar bonds do not automatically make a polar molecule.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 20

Independent chapter check: A molecule has four electron domains around its center, with two bonding pairs and two lone pairs. Predict electron-domain geometry and molecular shape; explain why bond angles need not be 109.5°.
Answer and explanation

The electron-domain arrangement is approximately tetrahedral and the molecular shape is bent. Lone-pair interactions and the actual chemical species alter angles; 109.5° is an ideal tetrahedral reference rather than an exact universal bond angle.

The electron-domain arrangement is approximately tetrahedral and the molecular shape is bent. Lone-pair interactions and the actual chemical species alter angles; 109.5° is an ideal tetrahedral reference rather than an exact universal bond angle.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 21

Write ammonium sulfate and check its charge.
Answer and explanation

(NH₄)₂SO₄: two +1 ammonium ions balance one −2 sulfate ion.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 22

What does the III in iron(III) chloride mean?
Answer and explanation

Each iron cation has charge +3, giving FeCl₃ with chloride ions.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 23

Independent chapter check: Write the formula for iron(III) sulfate and count all atoms per formula unit. Then name N₂O₃ using molecular prefixes.
Answer and explanation

Fe³⁺ and SO₄²⁻ require Fe₂(SO₄)₃: two Fe, three S and twelve O atoms. N₂O₃ is dinitrogen trioxide. The Roman numeral and prefixes serve different bookkeeping roles.

Fe³⁺ and SO₄²⁻ require Fe₂(SO₄)₃: two Fe, three S and twelve O atoms. N₂O₃ is dinitrogen trioxide. The Roman numeral and prefixes serve different bookkeeping roles.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 24

Count valence electrons in NO₃⁻.
Hints

Write the relationship first; substitute with consistent units.

Answer and explanation

24 electrons

5+3×6+1 = 24.

Problem 25

Why must a Lewis drawing conserve electron count?
Answer and explanation

The total follows elemental valence counts and ion charge; a drawing with extra electrons represents a different charge or invalid model.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 26

Independent chapter check: For NH₄⁺, count valence electrons, assign nitrogen’s formal charge for four N–H single bonds and no lone pair, and distinguish that charge from molecular shape.
Answer and explanation

Total valence electrons are 5+4(1)−1=8. Nitrogen formal charge is 5−0−4=+1 and each H is zero. The flat Lewis connectivity does not specify measured angles; the common molecular arrangement is tetrahedral.

Total valence electrons are 5+4(1)−1=8. Nitrogen formal charge is 5−0−4=+1 and each H is zero. The flat Lewis connectivity does not specify measured angles; the common molecular arrangement is tetrahedral.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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