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Atmospheric Chemistry

Periodic Graphics: The chemistry of snow and ice

Chemical educator and Compound Interest blogger Andy Brunning explores water’s unique behavior when temperatures plummet

by Andy Brunning
January 26, 2020 | APPEARED IN VOLUME 98, ISSUE 4



To download a PDF of this article, visit:

References used to create this graphic:

Brunning, Andy. “The Shapes of Snowflakes.” Compound Interest, Dec. 10, 2014.

Conners, Deanna. “How Snowflakes Get Their Shapes.” EarthSky, Jan. 28, 2019.

Lemonick, Sam. “Scientists Find the Smallest Number of Water Molecules That Can Form Ice.” Chemical & Engineering News, Nov. 7, 2019.

McNeill, V. Faye, and Meredith G. Hastings. “Ice in the Environment: Connections to Atmospheric Chemistry.” Environ. Res. Lett. (2008). DOI: 10.1088/1748-9326/3/4/045004.

A collaboration between C&EN and Andy Brunning, author of the popular graphics blog Compound Interest

To see more of Brunning’s work, go to To see all of C&EN’s Periodic Graphics, visit



This graphic was updated on Feb. 11, 2020, to clarify the plot of density versus temperature for water and ice. Originally, the plot depicted density versus temperature for liquid water at all temperatures. To better match the text in the graphic, the plot has been updated to depict density versus temperature for liquid water above 0 °C and for ice below 0 °C.

This graphic's references were updated also on Feb. 11, 2020, to add in missing entries and correct the spelling of Deanna Conners's name.



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Peter Wood (January 29, 2020 4:13 AM)
I do enjoy these graphics, they are excellent. However, something looks wrong with the 'Ice and Density' plot. Firstly, the gradient of the plot is steeper below zero (ice) than above zero (liquid water) which surprises me - however, a quick Google points to a Wikipedia page on ice which sees to support this (in mentioning that ice gets les dense as the temperature is lowered). I do appreciate that H2O is 'special' and that ice is a high-temperature solid. Secondly, the plot does not show the 8-9% volume change on freezing (the 'iceberg effect') so is this a plot of the density of liquid water (not ice) showing the density of supercooled water at temperatures below 0 Celsius?
Andy Brunning (January 30, 2020 4:51 PM)
Hi Peter,

Thanks for your comment. You're right that the graph shows the density of water at all of the temperatures shown. In retrospect, I can see how the inclusion of the ice cubes in the graphic is a bit deceptive here, as it implies that it also shows the density of ice.

As you say, the volume change on freezing means that the density of ice would be approximately 0.92 grams per centimetre cubed at 0˚C. I'll see if we can change the plot to make it more accurate.

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