Question

When two ice cubes are pressed over each other, they unite to form one cube. Which of the following forces is responsible to hold them together? (a) van der Waals forces (b) covalent attraction (c) ionic interaction (d) hydrogen bond formation

Short answer

(d) hydrogen bond formation

Step-by-step solution

Understand the Ice Cube Scenario

The problem involves two ice cubes being pressed together and forming one solid mass. We need to consider the molecular structure of ice and the potential forces that can act between them.

Consider Ice Structure

Ice is made up of water molecules (H₂O) arranged in a crystalline structure. These molecules form a network held together primarily by hydrogen bonds.

Identify the Force Involved

Since the ice is made of water molecules, which are polar and connected by hydrogen bonds, pressing the cubes together allows the networks of hydrogen bonds in each cube to merge, creating a larger hydrogen-bonded network.

Evaluate Other Options

Assess the other forces: van der Waals forces are weak and non-specific, covalent bonds involve shared electrons between atoms, and ionic interactions occur between positively and negatively charged ions. These are not prominent in ice cubes merging.

Key concepts

Molecular Structure of Ice

Ice, as we commonly know it, is the solid form of water. But why does it have such a rigid structure?
Understanding the molecular structure of ice gives us insight into its characteristics. Each water molecule in ice is composed of two hydrogen atoms bonded to one oxygen atom, forming a bent shape.
This shape is crucial because it makes water a polar molecule, leading to significant interactions between molecules.

• The oxygen atom is more electronegative than the hydrogen atoms, causing a partial negative charge on the oxygen and a partial positive charge on the hydrogens.
• These partial charges allow water molecules to attract each other, forming a tightly held structure.

This attraction is primarily due to hydrogen bonding, where the hydrogen of one water molecule is attracted to the oxygen of another. When ice forms, water molecules arrange themselves in a hexagonal crystalline pattern, enhancing stability.
This elegant design is what gives ice its distinctive solidity.

Polar Molecules

In chemistry, molecules like water that have a distribution of charges are called polar molecules. This property arises from the shape of the molecule and the electronegativity difference between its atoms.
In a polar molecule, there is an unequal sharing of electrons, leading to a dipole moment.

• Water, with its bent molecular shape and significant difference in electronegativity between hydrogen and oxygen, is a quintessential polar molecule.
• This polarity is key in the behavior of water, especially in its ability to form hydrogen bonds.

Hydrogen bonds, being a type of strong dipole-dipole attraction, explain why polar molecules like water stick together.
This characteristic greatly influences the formation of ice and its structural properties. The alignment of water molecules due to these bonds contributes extensively to ice's unique properties such as floating on water and its characteristic crystalline form.

Crystalline Structure of Water

When water freezes to form ice, it doesn’t just solidify randomly. Instead, it organizes into a specific crystalline structure, mostly hexagonal at normal atmospheric conditions.
This ordered arrangement is a result of each water molecule forming hydrogen bonds with up to four neighboring molecules in a lattice-like configuration.

• The hexagonal pattern is why ice appears less dense than liquid water, causing it to float.
• This structure can change under different pressure and temperature settings, but hexagonal ice is most common on Earth's surface.

Understanding the crystalline structure of ice helps explain why ice cubes stick together when pressed. The hydrogen bonds between the water molecules at the surfaces of two separate ice cubes can rearrange and link with each other under pressure, allowing them to join seamlessly. This reveals the remarkable interplay of water's physical properties driven by its hydrogen bonding capability in different states.