Question

Which of the following has highest intermolecular force of attraction ?

• A. Water at room temperature
• B. \(\text{CO}_2\) gas
• C. Ethyl alcohol
• D. Iron metal

Hint:

Generally, the strength of attractive forces between particles follows this trend: {Solids>Liquids>Gases}.
{Iron metal} is a solid held by strong metallic bonds.
{Water} and {Ethyl alcohol} are liquids with hydrogen bonds (strong type of intermolecular force, but weaker than metallic bonds).
{\(\text{CO}_2\) gas} has very weak London dispersion forces. Metallic bonds within a solid metal are very strong, making iron have the highest attractive forces among these options.

Answer 1

The Correct Option is D

Concept: Intermolecular forces (IMFs) are the forces of attraction or repulsion which act between neighboring entities: atoms, molecules, or ions. The strength of these forces determines the state of matter (solid, liquid, gas) at a given temperature and influences many physical properties. Generally, intermolecular forces are strongest in solids, weaker in liquids, and weakest in gases. Step 1: Analyze the state and type of bonding/forces in each option
(1) Water at room temperature (\(\text{H}_2\text{O}\)): Water is a liquid at room temperature. It is a polar molecule and exhibits strong hydrogen bonding (a special type of dipole-dipole attraction), in addition to London dispersion forces. Hydrogen bonds are relatively strong intermolecular forces.
(2) \(\text{CO}_2\) gas (Carbon Dioxide): Carbon dioxide is a gas at room temperature. It is a nonpolar molecule. The only intermolecular forces present are weak London dispersion forces. Gases inherently have very weak intermolecular forces because their particles are far apart and move randomly.
(3) Ethyl alcohol (\(\text{C}_2\text{H}_5\text{OH}\)): Ethyl alcohol is a liquid at room temperature. Like water, it is a polar molecule and can form hydrogen bonds due to the -OH group, as well as London dispersion forces.
(4) Iron metal (Fe): Iron is a solid at room temperature. In metals like iron, the atoms are held together by metallic bonds. Metallic bonds involve a "sea" of delocalized electrons shared among a lattice of positive metal ions. These are strong primary chemical bonds that hold the atoms together in the solid structure, and can be considered as very strong interatomic forces of attraction within the solid. While the term "intermolecular force" is typically used for forces between discrete molecules, in the context of comparing attractive forces holding substances together, metallic bonds in a solid are significantly stronger than the IMFs found in liquids like water or ethyl alcohol, and vastly stronger than those in gases. Step 2: Compare the strength of attractive forces Order of strength of forces (general comparison): Metallic bonds (in solids)>Hydrogen bonding (in liquids like water, alcohol)>Dipole-dipole forces (in other polar liquids)>London dispersion forces (in nonpolar substances, gases). Forces in solids are generally much stronger than in liquids, which are much stronger than in gases.
Iron metal (solid with strong metallic bonds)
Water and Ethyl alcohol (liquids with hydrogen bonding) - Hydrogen bonds are strong IMFs, but metallic bonds holding a solid metal lattice together are typically stronger.
\(\text{CO}_2\) gas (gas with only weak London dispersion forces) - Weakest attractive forces. The forces holding the atoms together in solid iron (metallic bonds) are significantly stronger than the intermolecular forces in liquid water or ethyl alcohol, or in gaseous \(\text{CO}_2\). Therefore, Iron metal has the highest intermolecular/interatomic force of attraction among the given options.