Question

Decide which one of the molecules listed below can form intermolecular hydrogen bonds, and then draw it, showing several molecules attached together by hydrogen bonds a. \(\mathrm{NaCl}\) b. \(\mathrm{MgCl}_{2}\) c. \(\mathrm{H}_{2} \mathrm{O}_{2}\) \(\mathrm{d} . \mathrm{CO}_{2}\)

Short answer

Among the given molecules, only molecule (c) \(\mathrm{H}_{2} \mathrm{O}_{2}\) can form intermolecular hydrogen bonds. The hydrogen bond can be represented as a dotted line between the oxygen atom of one molecule and the hydrogen atom of another molecule: O-H.....O-H (c) (c)

Step-by-step solution

Inspect molecule (a) \(\mathrm{NaCl}\)

\(\mathrm{NaCl}\) is an ionic compound consisting of sodium (Na) and chloride (Cl) ions, and it doesn't contain hydrogen atoms bonded to N, O, or F. Therefore, it cannot form intermolecular hydrogen bonds.

Inspect molecule (b) \(\mathrm{MgCl}_{2}\)

\(\mathrm{MgCl}_{2}\) is also an ionic compound, consisting of magnesium (Mg) and chloride (Cl) ions. It doesn't contain hydrogen atoms bonded to N, O, or F. Therefore, it cannot form intermolecular hydrogen bonds.

Inspect molecule (c) \(\mathrm{H}_{2} \mathrm{O}_{2}\)

\(\mathrm{H}_{2} \mathrm{O}_{2}\), also known as hydrogen peroxide, contains hydrogen atoms bonded to the highly electronegative oxygen atom. The oxygen atom in \(\mathrm{H}_{2} \mathrm{O}_{2}\) also contains two lone pairs, making it an eligible candidate for hydrogen bonding. Thus, \(\mathrm{H}_{2} \mathrm{O}_{2}\) can form intermolecular hydrogen bonds.

Inspect molecule (d) \(\mathrm{CO}_{2}\)

\(\mathrm{CO}_{2}\), the carbon dioxide molecule, doesn't contain any hydrogen atoms, and therefore it cannot form intermolecular hydrogen bonds.

Conclusion

Among the given molecules, only molecule (c) \(\mathrm{H}_{2} \mathrm{O}_{2}\) can form intermolecular hydrogen bonds. The hydrogen bond can be represented as a dotted line between the oxygen atom of one molecule and the hydrogen atom of another molecule, like this: O-H.....O-H (c) (c)

Key concepts

Ionic Compounds

Ionic compounds are fascinating because they are made up of ions. These ions are atoms or molecules that have gained or lost electrons, giving them a positive or negative charge. A classic example of an ionic compound is salt, or sodium chloride (\( \text{NaCl} \)). In ionic compounds, the positive and negative charges attract each other, forming a strong bond known as an ionic bond.
This is different from covalent bonds where atoms share electrons. Ionic bonds result in a lattice structure which is typically very stable.
These structures tend to have high melting and boiling points, making them quite durable in different conditions.Ionic compounds do not form hydrogen bonds because they lack the necessary hydrogen atoms bonded to highly electronegative atoms like nitrogen, oxygen, or fluorine. Instead, they rely on the electrostatic attraction between their charged particles to maintain their structure. This is a key reason why compounds like \( \text{NaCl} \) and \( \text{MgCl}_2 \) cannot participate in hydrogen bonding.

Hydrogen Peroxide

Hydrogen peroxide (\( \text{H}_2\text{O}_2 \)) is a simple yet intriguing compound. It consists of two hydrogen atoms and two oxygen atoms. The interesting part is the bond between these hydrogen atoms and their adjacent oxygen atoms.
This bond is what enables hydrogen peroxide to form intermolecular hydrogen bonds.
Hydrogen peroxide can interact through hydrogen bonding because of its unique structure where hydrogen is linked to a highly electronegative oxygen atom. Hydrogen bonds are a type of weak attraction that occurs when a hydrogen atom covalently bonded to an electronegative atom, such as oxygen, interacts with another electronegative atom's lone pair in a nearby molecule. This is represented by a dashed line, indicating the hydrogen bond.
Because of these hydrogen bonds, hydrogen peroxide molecules can "stick" together, leading to effects like increased viscosity when compared to molecules unable to form such bonds.

Electronegativity

Electronegativity is an essential concept in chemistry that describes an atom's ability to attract and hold electrons. This property is critical in determining how atoms will bond and interact with each other.
Atoms with high electronegativity, like oxygen and nitrogen, tend to attract electrons strongly, impacting molecular behavior and bonding patterns.
Hydrogen bonds form when hydrogen atoms are bonded to these electronegative atoms, creating a sort of "pull" on the bonding electrons. In hydrogen peroxide (\( \text{H}_2\text{O}_2 \)), oxygen's high electronegativity makes it possible for the molecule to participate in hydrogen bonding.The concept is a key factor not only in hydrogen bonding but also in understanding chemical reactivity and the properties of different substances. Knowing which atoms are more electronegative enables chemists to predict how molecules might interact or react under certain conditions.

Lone Pairs

Lone pairs refer to pairs of valence electrons that are not involved in covalent bonding. These electrons are found in the outer shell of an atom but do not participate in the formation of bonds with other atoms.
Lone pairs play an important role in intermolecular forces, particularly hydrogen bonding. In molecules like hydrogen peroxide (\( \text{H}_2\text{O}_2 \)), the oxygen atoms possess lone pairs that can engage in hydrogen bonding.
When dealing with hydrogen bonds, the presence of lone pairs provides sites that can interact with hydrogen atoms bonded to other electronegative atoms. This can significantly influence a compound's physical properties, such as boiling and melting points or its solubility in water.Understanding lone pairs helps in visualizing how molecules might align and bond with each other, shedding light on the unique properties of hydrogen bonding-compatible substances like hydrogen peroxide.