The SCIENCE Behind Snowflakes

Winter’s great natural marvels – snowflakes!

Detailed real snowflake

Did you know that chemistry is involved in the formation of snowflakes?

Each one that tumbles from the sky is an ice crystal made from frozen water molecules that join together in a lattice. They are formed through a process called nucleation.
A snowflake starts as a dust grain floating in a cloud. Water vapour in the air sticks to the dust grain and the resulting droplets turn into ice. Crystal faces appear on the frozen droplet.
Next, a prism forms with six faces and a cavity near the edges.
Faster growth on the corners causes six branches to sprout forming a hexagon shape, because the water molecules chemically bond into a hexagonal network.
When the crystal encounters a variation in temperature, more side branches sprout making the tips long and narrow. The growth of the tips slows and widens as the crystal falls into warmer air.
Finally, this unique and delicate structure falls to the earth, along with countless other snowflakes.

Are all snowflakes symmetrical?

The simple answer would be a yes and a no.
Yes, because many snowflakes are indeed symmetrical and intricate. This is because a snowflake’s shape reflects the internal order of the water molecules. Water molecules in the solid state such as in ice and snow form hydrogen bonds with one another. These ordered arrangements results in the symmetrical, hexagonal shape of the snowflake
No, because of uneven temperatures, the presence of dirt and other factors that may cause a snowflake to be lop-sided.

Can there be two identical snowflakes?

Once again, this statement is both true and false.
Yes, because it is possible for two snowflakes to look exactly alike and any given snowflake probably has had a good match at some point in history.
No, because as mentioned previously, many factors affect the structure of a snowflake which induces a constant change in response to environmental conditions. Hence, it is not likely for two snowflakes to be identical.

If water and ice are clear, then why does snow appear white?

Water is transparent because light enters and leaves in a straight line. Ice however is translucent because the path the light takes changes once it enters.
Snowflakes have so many light-reflecting surfaces they scatter the light into all of its colours and all these wavelengths combine to form white light.
Light from the sun is white but if the source of the light is a different colour (eg. there is a sunset) then the wavelengths of light entering, being refracted and reflected will combine to form the colour of the light source.

$A single wavelength being refracted through a prism (a) and white light being refracted through a prism (b)$

Figure 1: (a) shows a light source of one wavelength refract through a prism. (b) shows white light dispersed through a prism.

If you draw a snowflake, you’ll probably draw the familiar six-sided shape. However, snowflakes take a variety of different shapes (figure 2) depending on the temperature and the location of its formation.

Six examples of different snowflake shapes