The Simplified Chemistry of Snowflakes
Crystals are solids whose molecules are arranged in an orderly pattern, called a crystal lattice, when in a solid state (1). Snowflakes, with their unbelievably symmetrical and beautifully unearthly shapes, fall into this category.
Snowflakes form through nucleation, which is a process where water condenses around something -dust, pollen and even smoke particulates- to form ice. Nucleation takes place both in the formation of a new thermodynamic phase or in the self-assembly of particles, such as in the snowflakes’ case (2). The nucleation that forms our fellow snowflakes is quite a creative process. It never yields in the same structure twice. Jason Benedict, associate professor of chemistry from the University at Buffalo shares, “The shapes you observe are remarkably intricate. No two are exactly alike because the local environmental conditions — like the temperature, the humidity and the concentration of water molecules in the air — all affect where and how water molecules are going to attach to the crystal.” So in order to have identical snowflakes, identical environmental conditions would be needed. And on Earth, that’s quite impossible.
For example, it is known that there are 5 different snowflake shapes depending on the temperature of the environment. Thin, hexagonal plates between 0 to -4 degrees Celsius, needle-like branches between -4 and -6 degrees Celsius, hollow columns between -6 and -10, sector plates between -10 and -12 degrees Celsius and lacy hexagonal shapes between -12 and -16 degrees Celsius (see Figure 2).
But then, why do all of these shapes look so symmetrical? That has to do with a weak bond formation called ‘’hydrogen bonding’’. It results from the attractive force between a hydrogen atom that is covalently bonded to an electronegative atom (e.g. N, O, or F atom) and another electronegative atom (3). In crystallization, it is known that water molecules tend to align themselves to maximize attractive forces and minimize repulsive forces. This results in symmetrical, hexagonal shapes since because of this tendency, water molecules arrange themselves in predetermined spaces in a specific arrangement. This, in return, maintains symmetry (4).
Where this is a simplistic explanation of how snowflakes form and why they have such shapes, the process is much more complex, just as anything else on Earth.
Work Cited
1 & 3- Owen, Steven Michael, and Caroline Ahmed. Chemistry: For the IB Diploma. Cambridge University Press, 2015.
2 — “Nucleation.” ACS Publications, pubs.acs.org/doi/10.1021/cg1011633.
4 — Klesius, M. (2007). “The Mystery of Snowflakes”. National Geographic. 211 (1): 20. ISSN 0027–935
