Question

Liquid water is denser than ice due to (a) higher surface tension (b) hydrogen bonding (c) van der Waals forces (d) covalent bonding.

Short answer

(b) hydrogen bonding

Step-by-step solution

Identify the Property Related to Density

Density of a substance is determined by how closely packed its molecules are. Among the given options, we need to choose the one that directly affects the packing of water molecules.

Understand the Role of Hydrogen Bonding in Water

Hydrogen bonds are intermolecular forces that occur between water molecules due to the polarity of water. These bonds cause liquid water to have a unique structure that makes it denser than its solid form, ice.

Eliminate Irrelevant Options

Surface tension, van der Waals forces, and covalent bonding do not directly explain the density difference between liquid water and ice, as they do not significantly change between the two states compared to hydrogen bonding which is highly structure-dependent and responsible for the expanded crystalline structure in ice.

Select the Correct Answer

Based on the understanding of the structure of water, we conclude that hydrogen bonding is the most significant reason for the higher density of liquid water compared to ice.

Key concepts

Hydrogen Bonding

When exploring why liquid water is denser than ice, we stumble upon the critical role of hydrogen bonding. It's the hero of the water molecule narrative, ensuring that everything sticks together but not too tightly.

Each water molecule is like a tiny magnet, with a positive charge on one side and a negative charge on the other. This polarity makes water molecules attract each other, leading to the formation of hydrogen bonds. Think of them as tiny, invisible hands holding the water molecules in a specific arrangement. These are not your typical grab-and-hold-tight bonds; they're more like a casual handshake - firm yet flexible.

In liquid water, these handshakes are happening everywhere, which pulls the molecules closer together, resulting in a higher density. Ice, on the other hand, is like a rigid society where everyone stands at an arm's length. Here, the water molecules settle into a fixed, spacious structure, which makes ice less dense and enables it to float on liquid water.

• Key takeaway: Hydrogen bonding in liquid water pulls molecules closer, packing them tightly and increasing density.

Intermolecular Forces

You might wonder what exactly keeps water from being just a disorganized puddle of molecules. Well, the secret lies in intermolecular forces. These are forces between molecules, not within them (which would be intramolecular forces).

There are several types of intermolecular forces, but in water, hydrogen bonding is the star. It's like comparing different types of adhesives; while some, like van der Waals forces, are like sticky notes—light and temporary—hydrogen bonds are more like a double-sided tape, much stronger and more directional. They're what gives water its liquid form at room temperature and a solid form as ice.

Hydrogen bonds are very picky about whom they hold on to and how. In ice, they maintain an ordered, geometric arrangement, which creates more open space and results in lower density. When water melts, these bonds are free to move around, allowing the molecules to pack more closely.

• Core insight: Intermolecular forces, especially hydrogen bonds, dictate water's behavior in different states, influencing its density.

Molecular Structure of Water

Water's molecular structure is strikingly simple yet profoundly intricate. It's all about the angles and the two hydrogen atoms sticking out like mouse ears on the head of an oxygen atom, creating a bent shape. This V-like structure makes one side of the water molecule positively charged and the other side negatively charged.

The molecular structure of water is the reason behind its polar nature, which leads to the formation of hydrogen bonds. In the liquid state, water's structure allows molecules to move around, jostling and repositioning, which creates a denser configuration. However, once water turns into ice, the story changes. The molecules align in a way that maximizes hydrogen bonding but creates more space between them—think of a well-organized parking lot, with each car taking up just the right amount of space to fit the most vehicles.

The molecular structure also impacts how water interacts with other substances and transforms its physical properties. These unique characteristics allow it to dissolve many materials, making it a 'universal solvent'.

• Essential info: The bent molecular structure of water leads to polarity and hydrogen bonding, which significantly impact its liquid and solid density.