Chemistry Grade 11
Unit 2 Chemical Bonding1: Which statement best describes the octet rule?
A) Atoms tend to gain, lose, or share electrons to achieve eight electrons in their valence shell
B) All atoms must have exactly eight electrons in their outermost shell
C) Only noble gases can have eight valence electrons
D) Atoms with eight protons are most stable
Answer: A Explanation: The octet rule states that atoms tend to gain, lose, or share electrons to achieve a stable electron configuration with eight valence electrons, similar to noble gases.
2: Which type of chemical bonding involves the complete transfer of electrons from one atom to another?
A) Covalent bonding
B) Metallic bonding
C) Ionic bonding
D) Hydrogen bonding
Answer: C Explanation: Ionic bonding occurs when electrons are transferred from a metal to a nonmetal, forming oppositely charged ions that attract each other.
3: What is the correct Lewis electron-dot symbol for nitrogen (Group 15)?
A) :N:
B) :N·
C) ·N· with three dots around
D) ·N· with five dots around
Answer: D Explanation: Nitrogen has five valence electrons, so its Lewis symbol shows the element symbol N surrounded by five dots (one pair and three single electrons).
4: Which pair of elements is most likely to form an ionic compound?
A) C and O
B) Na and Cl
C) N and H
D) S and O
Answer: B Explanation: Sodium (metal) and chlorine (nonmetal) have a large electronegativity difference, favoring electron transfer and ionic bond formation.
5: Which ion does NOT follow the octet rule in its stable ionic compound?
A) Na⁺
B) O²⁻
C) Al³⁺
D) Li⁺
Answer: D Explanation: Li⁺ has only two electrons (helium configuration), which is stable for small atoms in Period 2; it is an exception to the octet rule.
6: Which property is characteristic of ionic compounds?
A) Low melting points
B) Conduct electricity in solid state
C) Solubility in nonpolar solvents
D) High melting and boiling points
Answer: D Explanation: Ionic compounds have strong electrostatic forces between ions, requiring high energy to break, resulting in high melting and boiling points.
7: What is the molecular geometry of a molecule with four bonding pairs and no lone pairs on the central atom?
A) Linear
B) Trigonal planar
C) Tetrahedral
D) Bent
Answer: C Explanation: According to VSEPR theory, four electron domains with no lone pairs adopt a tetrahedral geometry with bond angles of approximately 109.5°.
8: Which molecule has a bent molecular geometry?
A) CO₂
B) CH₄
C) H₂O
D) BF₃
Answer: C Explanation: Water has two bonding pairs and two lone pairs on oxygen, resulting in a bent geometry due to lone pair-bond pair repulsion.
9: Which intermolecular force is present in all covalent molecules?
A) Hydrogen bonding
B) Dipole-dipole forces
C) London dispersion forces
D) Ionic forces
Answer: C Explanation: London dispersion forces (instantaneous dipole-induced dipole) exist in all molecules, whether polar or nonpolar, due to temporary electron distribution fluctuations.
10: Which compound exhibits hydrogen bonding?
A) CH₄
B) HCl
C) NH₃
D) CO₂
Answer: C Explanation: Hydrogen bonding occurs when H is bonded to N, O, or F. NH₃ has N–H bonds, allowing hydrogen bonding between molecules.
11: In the electron-sea model of metallic bonding, what are the "sea" electrons?
A) Electrons tightly bound to individual atoms
B) Delocalized valence electrons free to move throughout the metal lattice
C) Core electrons involved in bonding
D) Electrons transferred to nonmetals
Answer: B Explanation: The electron-sea model describes metallic bonding as a lattice of positive metal ions surrounded by a "sea" of delocalized valence electrons that move freely.
12: Which property of metals is best explained by the electron-sea model?
A) Brittleness
B) Electrical conductivity
C) Low density
D) Transparency
Answer: B Explanation: Delocalized electrons can move easily through the metal lattice when a voltage is applied, allowing metals to conduct electricity.
13: According to valence bond theory, a covalent bond forms when:
A) Electrons are transferred between atoms
B) Atomic orbitals overlap and electrons are shared between atoms
C) Molecular orbitals are formed from linear combinations of atomic orbitals
D) Ions attract each other electrostatically
Answer: B Explanation: Valence bond theory states that a covalent bond results from the overlap of half-filled atomic orbitals, with electron pairs shared between the overlapping orbitals.
14: In molecular orbital theory, bonding molecular orbitals are:
A) Higher in energy than the atomic orbitals from which they are formed
B) Lower in energy than the atomic orbitals from which they are formed
C) Always filled before antibonding orbitals
D) Both B and C
Answer: D Explanation: Bonding MOs are lower in energy than the parent atomic orbitals and are filled before antibonding orbitals according to the Aufbau principle.
15: What is the bond order of O₂ according to molecular orbital theory?
A) 1
B) 2
C) 3
D) 4
Answer: B Explanation: O₂ has 12 valence electrons in MOs: (σ2s)²(σ*2s)²(σ2p)²(π2p)⁴(π*2p)². Bond order = ½[(8 bonding e⁻) – (4 antibonding e⁻)] = 2.
16: Which type of crystal is characterized by a lattice of positive ions surrounded by delocalized electrons?
A) Ionic crystal
B) Covalent network crystal
C) Metallic crystal
D) Molecular crystal
Answer: C Explanation: Metallic crystals consist of metal cations arranged in a lattice with delocalized valence electrons moving throughout the structure.
17: Diamond is an example of which type of crystal?
A) Ionic
B) Covalent network
C) Metallic
D) Molecular
Answer: B Explanation: Diamond has a giant covalent network where each carbon atom is covalently bonded to four others in a tetrahedral arrangement.
18: Which statement about Lewis structures is TRUE?
A) They show the three-dimensional shape of molecules
B) They represent only bonding electrons as dots
C) They show valence electrons as dots around element symbols
D) They cannot represent ions
Answer: C Explanation: Lewis electron-dot structures depict valence electrons as dots placed around the chemical symbol of an element.
19: Which molecule violates the octet rule by having an expanded octet?
A) BF₃
B) CO₂
C) PCl₅
D) NH₃
Answer: C Explanation: Phosphorus in PCl₅ has 10 valence electrons (five bonds), exceeding the octet; elements in Period 3 and beyond can expand their octet using d-orbitals.
20: Why do ionic compounds conduct electricity when molten or dissolved but not when solid?
A) Ions are fixed in position in the solid state but free to move when molten/dissolved
B) Electrons become delocalized only in solution
C) The octet rule is satisfied only in solution
D) Covalent bonds form in solution
Answer: A Explanation: In solid ionic compounds, ions are locked in a rigid lattice; when molten or dissolved, ions become mobile and can carry electric current.
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