Why are snowflakes six-pointed?

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Snowflakes exist in billions of different varieties. In fact, no two snowflakes are alike. But what unites them all is that each snowflake has a six-pointed shape. Let’s figure out what the reason is.

Many people think that snowflakes are frozen raindrops. This is not true. Snowflakes are actually sublimated water vapor. In fact, the moisture from the air in the gaseous state turns into ice crystals bypassing the liquid state. Such a process of «jumping» through the state of aggregation is called

Snowflake formation begins with the formation of a small hexagonal plate. As a snowflake falls through the atmosphere, moisture continues to sublimate and new ice crystals grow at the corners of this original hexagon. That is why no two snowflakes are alike: the path of each of them through the atmosphere is unique, and even the slightest changes in temperature, humidity, wind strength, etc. can have a large effect on the growth of ice crystals.

At the same time, in one snowflake, all six branches grow approximately the same, although complete symmetry is extremely rare — there are still minor differences between the branches. However, identical snowflakes can be obtained in laboratory conditions.

The hexagonal nature of the snowflakes is due to the geometry of the ice crystal lattice.

As you know, a water molecule consists of two oxygen atoms and one hydrogen atom. Considering how atoms exchange electrons in a water molecule, a hydrogen atom has a positive charge and oxygen atoms a negative one. The charged «end» of a molecule attracts the oppositely charged «end» of another water molecule. The so-called

In liquid water, hydrogen bonds between molecules constantly arise and break down due to high temperature, but when the water cools to a temperature close to zero degrees Celsius, the energy of the Brownian motion of the molecules also decreases and more stable hydrogen bonds begin to establish between the molecules. Each water molecule can form a hydrogen bond with four other molecules.

Under the influence of pressure, the molecules in the ice crystal tend to take the most energy efficient form. This shape is a tetrahedron in which at each vertex there is a water molecule that has a hydrogen bond with one of the other vertices. Several repeating structures derived from tetrahedrons are mathematically possible, but the most stable and energy efficient is the hexagonal structure. Such ice is called

There are other options for the crystal lattice of ice, but they usually require different conditions for the formation, for example

Thus, the hexagonal shape of the snowflakes is due to the fact that hexagonal cells underlie the ice crystal lattice.