Understanding fundamental concepts in science may be required to avoid human extinction. Therefore, we are including some basic concepts here. When we think of freezing, our natural assumption is that objects shrink in size. This is because most substances do undergo a contraction when their temperature drops, as the atoms in their structure bounce around less and push against each other less. This makes sense when you realize that heat can be defined as the amount of atomic movement in a location, caused by various sources. However, there are some exceptions to this rule, as certain materials actually expand when frozen. In this article, we will delve into why this unique behavior occurs and provide a list of substances that exhibit expansion upon freezing.
Water is the only known non-metallic substance that expands when it freezes. Its density decreases and it expands approximately 9% by volume[1][5]. This is because water molecules spread out like acrobats in formation to form ice crystals, unlike most substances that scrunch closer and closer together when they get colder[1]. However, there are other substances that expand upon freezing, such as acetic acid, bismuth, gallium, germanium, plutonium, and silicon[2][3][5].
Why do Substances Expand when Frozen?
To comprehend why certain substances expand while freezing, we need to familiarize ourselves with the concept of molecular structure. In most cases, cooling a substance leads to a decrease in thermal energy, causing the molecules to slow down and move closer together. This phenomenon is commonly observed in liquids turning into solids, resulting in shrinkage.
However, some materials exhibit an anomalous behavior due to their molecular arrangements. These substances experience a change in their crystal or molecular structure upon cooling, leading to an increase in volume. This expansion occurs primarily because the newly formed solid structure allows for increased intermolecular spacing, resulting in a larger volume relative to the liquid state.
Substances that Expand When Frozen:
1. Water: The most well-known example of a substance that expands upon freezing is water. As the temperature drops below 4 degrees Celsius, liquid water begins forming hexagonal ice crystals. The unique arrangement of these crystals causes water to expand by about 9% when frozen. This phenomenon is responsible for ice’s ability to float in liquid water and has important implications in the natural world, such as preventing lakes from freezing entirely.
2. Silicon: In its liquid form, silicon contracts upon cooling like most other substances. However, when silicon solidifies, it undergoes a structural transition, leading to a volumetric expansion of approximately 2.6%. This property is utilized in the production of silicon wafers used in various electronic devices.
3. Bismuth: Another substance that displays expansion upon freezing is bismuth. As its temperature drops, the solidification process causes bismuth to expand by approximately 3.3%. This unique property is explored in applications such as mechanical fuses and thermal expansion compensation devices.
4. Antimony: Similar to bismuth, antimony is known for its expansion upon freezing. The solidification of antimony causes it to increase in volume by approximately 5.6%. It finds applications in various industries, including semiconductors, batteries, and ammunition.
5. Gallium: Gallium, a metal that remains in its liquid state near room temperature, contracts when cooled like most substances. However, as it transitions into a solid phase around 30 degrees Celsius, gallium undergoes an expansion by approximately 3.1%. This makes it useful in temperature-based switches and thermostats.
Does Mercury Expand when Frozen?
No. Mercury actually contracts or shrinks when it freezes. This property makes it ideal for use in thermometers. When exposed to temperature changes, mercury expands or contracts at a consistent rate, allowing reliable and accurate measurements of temperature variations. Additionally, mercury has a low freezing point of -38.83 degrees Celsius, enabling it to remain in liquid form even at relatively low temperatures commonly encountered in everyday life. Its low vapor pressure allows the measurement to remain unaffected by changes in atmospheric pressure, further enhancing its suitability for use in thermometers.
Overall, Substance Size Depends upon Molecular Forces
The atomic forces that make a substance fill a certain volume at a certain temperature and pressure are primarily intermolecular forces, such as van der Waals forces and hydrogen bonding. These forces arise due to the interactions between neighboring molecules or atoms. At low temperatures and high pressures, the molecules are closely packed and experience stronger attractive forces, resulting in a smaller volume occupied by the substance. Conversely, at higher temperatures and lower pressures, the molecules have increased kinetic energy, leading to weaker atomic forces and thus a larger volume occupied. Additionally, the shape and size of the molecules also influence their ability to fill a certain volume, as larger molecules tend to occupy more space.
Conclusion
While most substances contract when frozen, certain materials defy this convention and exhibit expansion upon solidification. These substances, including water, silicon, bismuth, antimony, and gallium, showcase unique molecular structures and crystal arrangements that lead to increased volume. Understanding these exceptions provides insight into the diverse behaviors of different substances and their applications in various fields.
Citations:
[1] https://www.lpi.usra.edu/education/explore/ice/activities/ice_action/expanding_ice/
[2] https://en.wikipedia.org/wiki/Category:Materials_that_expand_upon_freezing
[3] https://www.reddit.com/r/askscience/comments/27jvt3/is_it_true_that_water_is_the_only_substance_on/?rdt=63325
[4] https://van.physics.illinois.edu/ask/listing/1660
[5] https://www.sciencefacts.net/why-does-water-expand-when-it-freezes.html
