Bonding & polarity: Chemistry Regents Practice

The ability of metals such as copper to conduct electric current is best explained by the presence of

• (A) positive and negative ions locked in a crystal lattice
• (B) hydrogen bonds between neighboring molecules
• (C) shared pairs of electrons fixed between two atoms
• (D) mobile valence electrons ✓

Metallic bonding models a metal as positive kernels surrounded by a sea of mobile (delocalized) electrons; these free electrons carry charge, giving metals their conductivity, malleability, and luster.

Which formula represents a molecule containing a nonpolar covalent bond?

• (A) CaCl2
• (B) NaCl
• (C) Cl2 ✓
• (D) HCl

A nonpolar covalent bond forms between two identical atoms sharing electrons equally, as in Cl2, since the electronegativity difference is zero.

Which bond is classified as a nonpolar covalent bond?

• (A) Cl-Cl ✓
• (B) Na-Cl
• (C) H-O
• (D) H-F

A bond between two atoms of the same element, like Cl-Cl, has an electronegativity difference of zero, meaning the bonding electrons are shared equally. This makes it a nonpolar covalent bond, unlike H-F, H-O (polar covalent) or Na-Cl (ionic).

The electronegativity of hydrogen is 2.2 and the electronegativity of chlorine is 3.16. Using this information, explain why the bond formed between a hydrogen atom and a chlorine atom in HCl is classified as a polar covalent bond.

Bond type is determined by electronegativity difference: differences from 0.0-0.4 are generally nonpolar covalent, 0.4-1.7 are polar covalent, and differences greater than 1.7 are generally ionic. HCl's difference of 0.96 places it in the polar covalent range.

The electronegativity of hydrogen is 2.20 and the electronegativity of chlorine is 3.16. Calculate the electronegativity difference for a bond between these two atoms, and use this value to classify the bond as ionic, polar covalent, or nonpolar covalent.

Electronegativity difference indicates how unequally electrons are shared in a bond: small differences (0 to 0.4) are nonpolar covalent, moderate differences (0.4 to 1.7) are polar covalent, and large differences (greater than 1.7) are ionic.

Compare the bonding in a sample of KCl(s) to the bonding in a sample of Cl2(g). Identify the type of bond in each substance and explain the difference using electronegativity.

Bond type is determined by the electronegativity difference between bonded atoms: a large difference (as between a metal and a nonmetal) results in electron transfer and an ionic bond, while a difference of zero (as between two identical nonmetal atoms) results in equal sharing of electrons and a nonpolar covalent bond.

The electronegativity of hydrogen is 2.20, and the electronegativity of chlorine is 3.16. Using these values, calculate the electronegativity difference between the two atoms in a molecule of HCl and classify the bond between H and Cl as ionic, polar covalent, or nonpolar covalent.

Bond type is determined from the electronegativity difference between the two bonded atoms: small differences (roughly 0 to 0.4) indicate nonpolar covalent bonds, moderate differences (roughly 0.4 to 1.7) indicate polar covalent bonds, and large differences (greater than 1.7) indicate ionic bonds.

Which type of bond forms between a metal and a nonmetal, as in $\mathrm{NaCl}$ ?

• (A) metallic
• (B) ionic ✓
• (C) polar covalent
• (D) nonpolar covalent

A large electronegativity difference (metal + nonmetal) transfers electrons, forming oppositely charged ions held by an ionic bond.

A bond between a metal and a nonmetal that involves the transfer of electrons is best classified as

• (A) nonpolar covalent
• (B) ionic ✓
• (C) metallic
• (D) polar covalent

When a metal gives electrons to a nonmetal, the resulting oppositely charged ions attract, an ionic bond.

According to electronegativity values in Reference Table S, which bond is the most polar?

• (A) $\mathrm{H}\text{–}\mathrm{I}$
• (B) $\mathrm{H}\text{–}\mathrm{Cl}$
• (C) $\mathrm{H}\text{–}\mathrm{Br}$
• (D) $\mathrm{H}\text{–}\mathrm{F}$ ✓

The bond with the largest electronegativity difference has the most unequal electron sharing and is therefore the most polar; F is the most electronegative element on Table S.

Which molecule contains polar covalent bonds but is itself nonpolar because of its symmetrical shape?

• (A) $\mathrm{NH}_3$
• (B) $\mathrm{CO}_2$ ✓
• (C) $\mathrm{H}_2\mathrm{O}$
• (D) $\mathrm{HCl}$

Molecular polarity depends on both bond polarity and shape; CO2 is linear and symmetric, so its two equal bond dipoles cancel, making the whole molecule nonpolar even though each bond is polar.

Water ($\mathrm{H}_2\mathrm{O}$) boils at a much higher temperature than most molecules of similar size. This unusually high boiling point is best explained by

• (A) hydrogen bonding between water molecules ✓
• (B) ionic bonds between water molecules
• (C) the breaking of covalent bonds within each water molecule
• (D) metallic bonding among the molecules

Boiling point depends on the strength of intermolecular forces; water molecules attract one another through relatively strong hydrogen bonds, so extra energy is needed to pull them apart, raising the boiling point.

Which molecule contains polar covalent bonds but is a nonpolar molecule overall due to its symmetric shape?

• (A) $H_2O$
• (B) $CO_2$ ✓
• (C) $HCl$
• (D) $NH_3$

Carbon dioxide has two polar C=O bonds, but because the molecule is linear and symmetric, the two bond dipoles point in opposite directions and cancel, making the overall molecule nonpolar. HCl, NH3, and H2O are all polar molecules because their bond dipoles do not cancel.

Based on electronegativity differences from the Periodic Table, which of these molecules contains the most polar covalent bond?

• (A) $HCl$
• (B) $HF$ ✓
• (C) $HBr$
• (D) $HI$

Bond polarity increases with electronegativity difference between the bonded atoms; fluorine has the highest electronegativity of the halogens listed, so H-F has the largest electronegativity difference and is the most polar bond.

Using electronegativity values from the Periodic Table, which bond listed below is most polar?

• (A) H-Cl
• (B) H-Br
• (C) H-I
• (D) H-F ✓

Bond polarity increases with the difference in electronegativity between the bonded atoms. Fluorine has the highest electronegativity of the halogens, so the H-F bond has the largest electronegativity difference and is the most polar bond among the choices. A common error is picking H-I, mistakenly reasoning that larger atoms make more polar bonds.

Based on electronegativity differences, which of these hydrogen halide bonds is the most polar?

• (A) H-Cl
• (B) H-I
• (C) H-F ✓
• (D) H-Br

Bond polarity increases with the difference in electronegativity between the two bonded atoms; fluorine has the highest electronegativity of the halogens, so the H-F bond has the largest electronegativity difference and is the most polar bond among the choices. Students who pick H-I often mistakenly think a larger atom size means more polarity, but polarity depends on electronegativity difference, not atomic size.

The electronegativity of sodium is 0.9, chlorine is 3.2, and oxygen is 3.4. Using electronegativity differences, determine the type of bond (ionic, polar covalent, or nonpolar covalent) present in (1) the bond between Na and Cl in NaCl, and (2) the bond between two oxygen atoms in $O_2$. Justify each answer using the calculated electronegativity difference.

Bond type can be predicted from electronegativity difference: differences greater than about 1.7 indicate ionic bonding, small nonzero differences indicate polar covalent bonding, and a difference of 0 (as between two atoms of the same element) indicates nonpolar covalent bonding.

The electronegativity of chlorine is 3.16 and the electronegativity of hydrogen is 2.20. Determine the electronegativity difference between these two atoms in a molecule of HCl, and use this difference to identify the type of bond (nonpolar covalent, polar covalent, or ionic) present in HCl.

Bond type can be predicted from electronegativity difference: roughly 0 to 0.4 is nonpolar covalent, 0.4 to 1.7 is polar covalent, and greater than 1.7 is generally ionic. A difference of 0.96 falls in the polar covalent range.

The electronegativity value for hydrogen is 2.1 and the electronegativity value for chlorine is 3.0. Calculate the electronegativity difference for a bond between hydrogen and chlorine, and identify the type of bond (nonpolar covalent, polar covalent, or ionic) that forms between these two atoms.

Bond type is classified by the magnitude of the electronegativity difference between the two bonded atoms: small differences give nonpolar covalent bonds, intermediate differences give polar covalent bonds, and large differences give ionic bonds; a difference of 0.9 falls in the polar covalent range.

The electronegativity of hydrogen is 2.2, and the electronegativity of chlorine is 3.2. Calculate the electronegativity difference for a bond formed between an atom of hydrogen and an atom of chlorine. Based on this difference, identify the type of bond (nonpolar covalent, polar covalent, or ionic) that forms between H and Cl.

Bond type is determined by the electronegativity difference between the two bonded atoms: differences less than about 0.4 indicate nonpolar covalent bonds, differences between about 0.4 and 1.7 indicate polar covalent bonds, and differences greater than about 1.7 indicate ionic bonds. Here a difference of 1.0 places the H-Cl bond in the polar covalent range.

Which molecule contains polar covalent bonds but is a nonpolar molecule overall?

• (A) $CO_2$ ✓
• (B) $NH_3$
• (C) $HF$
• (D) $H_2O$

Molecular polarity depends on both bond polarity and molecular geometry. In linear, symmetric CO2 the two polar C=O bond dipoles point in opposite directions and cancel exactly, making the molecule nonpolar overall, unlike bent H2O or trigonal pyramidal NH3, which have uncancelled dipoles.

Based on electronegativity values found on the Periodic Table reference table, which bond is the most polar?

• (A) H-Br
• (B) H-Cl
• (C) H-F ✓
• (D) H-I

Bond polarity increases with the difference in electronegativity between the two bonded atoms. Fluorine is the most electronegative element on the periodic table, so the H-F bond has the greatest electronegativity difference and is therefore the most polar bond among the choices. Electronegativity difference (and thus polarity) decreases going down Group 17 from F to I.

The electronegativity of calcium is 1.00 and the electronegativity of chlorine is 3.16. Based on this electronegativity difference, identify the type of bond (ionic, polar covalent, or nonpolar covalent) that forms between calcium and chlorine atoms in $CaCl_2$, and explain your reasoning.

The size of the electronegativity difference between bonded atoms indicates how equally electrons are shared. A large difference, as between calcium and chlorine, means chlorine attracts the bonding electrons so strongly that they are transferred, producing an ionic bond.

Using electronegativity values from the Periodic Table, calculate the electronegativity difference between the hydrogen atom (electronegativity 2.2) and the chlorine atom (electronegativity 3.16) in a molecule of HCl. Based on this difference, identify the type of bond present in HCl.

The magnitude of the electronegativity difference between two bonded atoms determines the character of the bond: small differences give nonpolar covalent bonds, intermediate differences give polar covalent bonds, and large differences give ionic bonds.