Types of Chemical Bonds - AP Chemistry

The electronegativity of fluorine is greater than the electronegativity of bromine. Which of the following is the best explanation for this difference?
Answer: Fluorine has a smaller atomic radius, resulting in a stronger electrostatic attraction between its nucleus and bonding electrons. Electronegativity is an atom's ability to attract shared electrons. According to Coulomb's Law, the force of attraction increases as the distance between charges decreases. Fluorine is in period 2 while bromine is in period 4. Fluorine's valence electrons (and any bonding electrons) are in an energy level closer to the nucleus, resulting in a smaller atomic radius. This shorter distance leads to a stronger attraction from the nucleus, hence a higher electronegativity.
Silicon carbide, SiC, is a very hard, high-melting-point solid that is insoluble in water. Which type of chemical bonding best accounts for these properties?
Answer: Network covalent bonding The properties of being extremely hard and having a very high melting point are characteristic of network covalent solids. In these substances, atoms are held together by a continuous network of strong covalent bonds throughout the crystal. Silicon and carbon have similar electronegativities and form such a network. Ionic solids are hard but brittle. Metallic solids are malleable. Molecular solids have low melting points because they are held together by weak intermolecular forces.
In $\mathrm{CH_4(g)}$ , the electronegativity of C is 2.5 and that of H is 2.1, so $\Delta EN = 0.4$ . Which classification best describes a C–H bond in methane?
Answer: Nonpolar covalent bond This question tests the skill of classifying bonds based on electronegativity differences. The electronegativity difference between C and H is 0.4, which is at the boundary between nonpolar and polar covalent bonds, but is typically classified as nonpolar covalent. In CH₄, the small electronegativity difference means electrons are shared nearly equally between carbon and hydrogen atoms, resulting in minimal polarity in each C-H bond. Students might incorrectly choose polar covalent bond (B) by strictly applying the ΔEN = 0.4 cutoff, but C-H bonds are conventionally treated as nonpolar due to their minimal dipole moment. When ΔEN is exactly 0.4 or very close to it, especially for C-H bonds, classify as nonpolar covalent.
Which of the following molecules contains both polar covalent bonds and nonpolar covalent bonds?
Answer: $H_2O_2$ To have both polar and nonpolar covalent bonds, a molecule must contain bonds between different atoms with a significant electronegativity difference (polar) and bonds between identical atoms (nonpolar). Hydrogen peroxide ( $H_2O_2$ ) has the structure H-O-O-H. The O-H bonds are polar covalent due to the electronegativity difference between oxygen and hydrogen. The O-O bond is nonpolar covalent because the two oxygen atoms have identical electronegativity.
In copper metal, Cu atoms are held together by attraction between metal cations and a sea of mobile, delocalized electrons. What type of bonding best describes solid copper?
Answer: Metallic This question tests the ability to identify the type of chemical bond in transition metals. In solid copper, Cu atoms are held by metallic bonding via delocalized electrons, explaining its conductivity. The electron sea attracts cations together. Metallic is specific to metals. A tempting distractor is ionic, but it is incorrect for pure elements, misconceptions come from confusing metallic lattices with ionic ones. Identify metallic bonds by metallic properties like luster and malleability.
A bond forms between potassium and bromine in KBr, producing $\text{K}^+$ and $\text{Br}^-$ . Which classification best describes the bond between K and Br?
Answer: Ionic This question tests the skill of classifying chemical bonds based on ion formation. In KBr, potassium transfers its valence electron to bromine, forming K⁺ and Br⁻ ions, which clearly indicates ionic bonding. The electronegativity difference between K (≈0.8) and Br (≈2.8) gives ΔEN ≈ 2.0, well above the 1.7 threshold for ionic bonds. The complete electron transfer creates discrete ions that attract each other through electrostatic forces in the solid state. Students might incorrectly choose polar covalent (D), not recognizing that the formation of ions with full charges distinguishes ionic from covalent bonding. When a metal from Group 1 bonds with a halogen from Group 17, the result is always an ionic bond due to the large electronegativity difference and tendency for complete electron transfer.
In carbon dioxide, the C–O electronegativity difference is about $1.0$ (C $\approx 2.5$ , O $\approx 3.5$ ), meaning each C–O bond shares electrons unequally. What type of bond best describes a C–O bond in $\text{CO}_2$ ?
Answer: Polar covalent This question tests the ability to identify the type of chemical bond based on electronegativity in linear molecules. In CO₂, each C-O bond has ΔEN ≈ 1.0, leading to unequal electron sharing and polar covalent character. The oxygen atoms pull electrons more, creating partial charges, though the molecule is nonpolar overall due to symmetry. Polar covalent bonds are defined by 0.5 < ΔEN < 1.7 in covalent sharing. A tempting distractor is nonpolar covalent, but it is incorrect due to the ΔEN, misconceptions come from confusing molecular polarity with bond polarity. Distinguish bond types by focusing on individual bond ΔEN, not overall molecule symmetry.
In potassium chloride, K transfers an electron to Cl (K is a metal, Cl is a nonmetal), forming $\text{K}^+$ and $\text{Cl}^-$ . What type of bond best describes the interaction in KCl?
Answer: Ionic This question tests the ability to identify the type of chemical bond based on electron transfer between metal and nonmetal atoms. In potassium chloride, potassium, a metal, transfers an electron to chlorine, a nonmetal, forming K⁺ and Cl⁻ ions. The bond is ionic due to the electrostatic attraction between these oppositely charged ions, typical for large electronegativity differences and metal-nonmetal combinations. Ionic bonds are common in compounds like salts that form crystal lattices. A tempting distractor is polar covalent, but it is incorrect because it involves sharing, not transfer, misconceptions stem from ignoring the metal-nonmetal distinction. To determine bond types, evaluate if electron transfer occurs by checking periodic table positions and ΔEN > 1.7.
In calcium fluoride, Ca forms $\text{Ca}^{2+}$ and each F forms $\text{F}^-$ . The compound consists of ions arranged in a crystal lattice. What type of bond best describes CaF $_2$ ?
Answer: Ionic This question tests the ability to identify the type of chemical bond in ionic compounds with polyatomic ions. In CaF₂, calcium transfers electrons to fluorine, forming Ca²⁺ and F⁻ ions in a crystal lattice, indicative of ionic bonding. The metal-nonmetal combination and high ΔEN support electron transfer. Ionic bonds lead to strong electrostatic attractions in solids. A tempting distractor is polar covalent, but it is incorrect for complete transfer, misconceptions stem from high ΔEN but ignoring ionic character. Use ion formation and lattice structure to identify ionic bonds in metal-nonmetal compounds.
In hydrogen chloride, HCl, the electronegativity values are approximately $EN(\text{H}) = 2.2$ and $EN(\text{Cl}) = 3.0$ (so $\Delta EN \approx 0.8$ ). Which classification best describes the H–Cl bond?
Answer: Polar covalent This question tests the skill of determining bond type from electronegativity differences. The H-Cl bond has ΔEN ≈ 0.8, which falls in the range of 0.5-1.7, indicating a polar covalent bond where electrons are shared unequally. The chlorine atom attracts the bonding electrons more strongly than hydrogen, creating a partial negative charge on Cl and partial positive on H. Students might incorrectly choose ionic (A) by overestimating the electronegativity difference or thinking all metal-nonmetal bonds are ionic, not recognizing that H behaves as a nonmetal in bonding. The key strategy is to calculate ΔEN and apply the standard ranges: polar covalent bonds have moderate ΔEN values where electrons are shared but unequally.
A pure, solid substance readily dissolves in water, but the resulting aqueous solution does not conduct electricity. The bonding in the substance is best described as which of the following?
Answer: Polar molecular covalent For a substance to dissolve in water, it must have polar characteristics or be ionic. Since the resulting solution does not conduct electricity, the substance does not form mobile ions when dissolved. This rules out ionic compounds. Metals do not dissolve in water. Network covalent solids are generally insoluble. A polar molecular covalent substance (like sugar) can dissolve in water due to attractions between its polar molecules and water molecules, but it remains as neutral molecules in solution, which do not conduct electricity.
Which of the following diatomic species contains a nonpolar covalent bond?
Answer: O₂ A nonpolar covalent bond forms between two atoms with identical or nearly identical electronegativity. In the O₂ molecule, the bond is between two oxygen atoms, which have the same electronegativity. Therefore, the electronegativity difference is zero, and the bond is purely nonpolar covalent. CO, HF, and KCl all consist of atoms with different electronegativities, resulting in polar covalent or ionic bonds.
Consider the bonds in $F_2$ , $CF_4$ , and $BeF_2$ . Which of the following lists these bonds in order of increasing ionic character?
Answer: $F_2 < CF_4 < BeF_2$ Ionic character increases with an increasing difference in electronegativity ( $\Delta EN$ ) between the bonded atoms. In $F_2$ , the bond is F-F, so $\Delta EN = 0$ (purely covalent, zero ionic character). In $CF_4$ , the bond is C-F. The $\Delta EN$ is significant (polar covalent). In $BeF_2$ , the bond is Be-F. Beryllium has a much lower electronegativity than carbon, so the $\Delta EN$ for Be-F is much larger than for C-F (highly ionic character). Therefore, the order of increasing ionic character is $F_2 < CF_4 < BeF_2$ .
In magnesium oxide, MgO, magnesium forms $\text{Mg}^{2+}$ and oxygen forms $\text{O}^{2-}$ in an ionic lattice. Which classification best describes the bond between Mg and O?
Answer: Ionic This question tests the skill of classifying chemical bonds based on ion formation and electron transfer. In MgO, magnesium loses two electrons to form Mg²⁺ while oxygen gains two electrons to form O²⁻, demonstrating complete electron transfer characteristic of ionic bonding. The electronegativity difference between Mg (≈1.3) and O (≈3.4) gives ΔEN ≈ 2.1, well above the 1.7 threshold typically associated with ionic bonds. The resulting ions arrange in a crystal lattice held together by strong electrostatic attractions. Students might incorrectly choose polar covalent (B), not recognizing that the formation of discrete ions with full charges indicates ionic rather than covalent bonding. To identify ionic bonds, look for evidence of complete electron transfer, ion formation, and typically a metal bonded to a nonmetal with large ΔEN.
In lithium bromide, Li forms $\text{Li}^+$ and Br forms $\text{Br}^-$ . The attraction is primarily between oppositely charged ions. What type of bond best describes LiBr?
Answer: Ionic This question tests the ability to identify the type of chemical bond in alkali metal halides. In LiBr, lithium transfers an electron to bromine, forming Li⁺ and Br⁻ ions attracted electrostatically in an ionic bond. The metal-nonmetal pair and large ΔEN confirm transfer. Ionic compounds like LiBr are crystalline solids. A tempting distractor is polar covalent, but it is incorrect for electron transfer, misconceptions come from underestimating ΔEN impact. Classify as ionic when metals and nonmetals form compounds with high ΔEN.
The bonding in which of the following substances is best described as ionic?
Answer: BaF₂ Ionic bonds typically form between a metal and a nonmetal, involving the transfer of electrons. BaF₂ is composed of barium, an alkaline earth metal, and fluorine, a halogen (a nonmetal). This combination results in ionic bonding. HCl and CO₂ are formed from two nonmetals, resulting in covalent bonding. Fe is a metallic element, and the bonding within it is metallic.
Which of the following pairs of elements would form the most polar single covalent bond?
Answer: B and Cl The polarity of a covalent bond is determined by the difference in electronegativity between the two bonded atoms. The greater the difference, the more polar the bond. Comparing the electronegativity differences for the given pairs: Boron (EN ≈ 2.0) and Chlorine (EN ≈ 3.2) have a difference of about 1.2. Nitrogen (EN ≈ 3.0) and Fluorine (EN ≈ 4.0) have a difference of about 1.0. Sulfur (EN ≈ 2.6) and Oxygen (EN ≈ 3.4) have a difference of about 0.8. Carbon (EN ≈ 2.6) and Hydrogen (EN ≈ 2.2) have a small difference of about 0.4. The largest electronegativity difference is between B and Cl, making it the most polar bond among the choices.
Which of the following elements will form a bond with oxygen that has the least ionic character?
Answer: S A bond with the least ionic character will have the smallest difference in electronegativity between the two atoms. Oxygen (EN ≈ 3.4) is a highly electronegative element. We need to find the element with an electronegativity closest to oxygen's. Sulfur (EN ≈ 2.6) is in the same group as oxygen and has the closest electronegativity value among the choices. The other elements are metals (Li, Ca, Al) with much lower electronegativities, leading to much larger differences and bonds with high ionic character.
In solid copper, Cu(s), bonding is described as a lattice of metal cations in a sea of delocalized electrons. Which classification best describes the bonding in Cu(s)?
Answer: Metallic bond This question tests the skill of identifying metallic bonding based on structural description. Copper forms a metallic bond, characterized by metal cations surrounded by a "sea" of delocalized electrons that can move freely throughout the structure. This electron mobility explains why metals conduct electricity and heat well, as the electrons are not localized between specific atoms but belong to the entire metallic lattice. Students might incorrectly choose ionic bond (A) because they see the word "cations," but ionic bonds involve discrete anion-cation pairs, not delocalized electrons. When a substance is described as having metal cations in a sea of delocalized electrons, it's always metallic bonding.
In solid sodium chloride, NaCl, sodium is a metal and chlorine is a nonmetal, and the electronegativity difference is large ( $\Delta\chi\approx2.1$ ). Which best classifies the bonding between Na and Cl in NaCl?
Answer: Ionic This question tests the skill of identifying ionic bonds based on electronegativity differences and element types. The Na-Cl bond has a large electronegativity difference of 2.1, which exceeds the typical threshold of 1.7-2.0 for ionic bonding. In ionic bonds, electrons are essentially transferred from the metal (Na) to the nonmetal (Cl), creating Na⁺ cations and Cl⁻ anions that are held together by electrostatic attraction. The combination of a metal with a nonmetal and the large electronegativity difference both indicate ionic bonding. Students might incorrectly choose polar covalent (A), thinking any bond with unequal electron distribution is polar covalent, but when Δχ exceeds 1.7 and involves a metal-nonmetal pair, the bond is ionic rather than covalent. To identify ionic bonds, check for both a large electronegativity difference (Δχ ≥ 1.7) and the presence of a metal bonding with a nonmetal.

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