Question

In an ice crystal, how many hydrogen bonds exist between each water molecule and the surrounding water molecules?

Short answer

Each water molecule forms four hydrogen bonds in an ice crystal.

Step-by-step solution

Visualize the Water Molecule Structure

Each water molecule in an ice crystal forms a tetrahedral arrangement with other water molecules. Visualize this structure as a central water molecule surrounded by others in a specific geometric pattern.

Identify the Hydrogen Bonds

In a tetrahedral structure, each water molecule in an ice crystal can form hydrogen bonds with four nearby water molecules. Two of these are formed by the hydrogen atoms of the central molecule, and the other two are formed by the oxygen atom's lone pairs.

Count the Hydrogen Bonds

Since each water molecule participates in four hydrogen bonds in an ice crystal, the number of hydrogen bonds per water molecule is four. This consistent bonding pattern is what contributes to the stability and unique properties of ice.

Key concepts

Water Molecule Structure

Water is a fascinating molecule with the chemical formula H extsubscript{2}O.
It consists of two hydrogen atoms bonded to one oxygen atom. These atoms come together in a bent shape, known as the "V" or "angular" configuration.
In this structure:

• Each hydrogen atom shares an electron with the oxygen atom, forming a polar covalent bond.
• The molecule is polar because of the unequal sharing of electrons, leading to partial positive charges on the hydrogen atoms and a partial negative charge on the oxygen atom.

This polarity is crucial because it allows water molecules to form hydrogen bonds, which are weak interactions that occur between the partially positive hydrogen of one molecule and the partially negative oxygen of another. This unique configuration plays an integral role in water's ability to create a variety of structures and its distinctive properties in different states.

Tetrahedral Arrangement

In its solid form, water molecules organize into a form called a tetrahedral arrangement.
Imagine each water molecule surrounded by four others in a 3D pattern resembling a pyramid with a triangular base.
This structure is key to forming the stable network found in ice. Here's how it works:

• The oxygen atom of one water molecule can form two hydrogen bonds using its lone pairs with the hydrogen atoms of two different water molecules.
• Additionally, each hydrogen atom of the central water molecule can bond with the oxygen atom of another water molecule nearby.

Together, these interactions result in each water molecule forming four hydrogen bonds, contributing to a highly ordered and open crystal lattice that gives ice its lower density compared to liquid water.

Ice Crystal Properties

The tetrahedral arrangement in ice leads to several distinct properties that set it apart from liquid water.
One of the most notable is that ice is less dense than its liquid counterpart, which is why ice floats. This happens because:

• The organized hydrogen bonding forms an open hexagonal lattice, creating more space between molecules compared to liquid water where the molecules are more closely packed.
• This increased spacing reduces the density of ice.

Moreover, the solid structure provided by these consistent hydrogen bonds grants ice stability and a relatively high melting point for a substance with such small molecules. These properties emphasize the incredible versatility and robustness of hydrogen bonds and showcase the fascinating nature of water as it transitions between states.