We are continuing our study of atmospheric science using lesson plans from UCAR with our own twist. The activity today closely followed Introduction to the Atmosphere – Activity 3.
Today’s activity was short, but packed with important concepts.
First we watched the following short videos from the Canadian Museum of Nature:
I emphasized to the boys that not all molecules are polar. The polarity of water gives it properties that are important. The polarity is introduced due to an uneven sharing of the electrons that create the bond between hydrogen and oxygen.
After viewing the videos, we used paper plates and M&Ms to make models of water in it’s solid, liquid and gas states.
C chose to use single M&Ms to represent each water molecule. This representation allowed us to shake the plate rapidly to represent gas molecules and more slowly when representing molecules in the liquid state. He glued the molecules to the plate when representing ice and drew in the hydrogen bonds.
We briefly discussed that it is a combination of pressure AND temperature that effect the state of matter, but for our purposes we would be discussing water at a constant atmospheric pressure. We also reviewed the temperatures at which state changes begin to occur in both Celsius and Fahrenheit at atmospheric pressure.
E chose to emphasize the H2O structure of water. The disadvantage was we couldn’t shake the gas and liquid plates, but we were more clearly able to see the need to line up the hydrogens facing the oxygen in the solid state.
Both boys used a roughly equivalent number of molecules in their solid and liquid representations. We ended up moving a couple of molecules from solid over to liquid to emphasize that ice is less dense than water, which they knew but just didn’t think to count the number of molecules in each plate.
The shape of the arrangement and hydrogen bonds didn’t turn out exactly right in the models, but they did understand the concept of attraction between slight positive and negative charges that are easily overcome at higher temperatures (faster vibration).
Between the videos and the models the boys were able to clearly understand why ice is less dense than water and why that is a “special” case. They were also able to grasp that hydrogen bonding between molecules is a much weaker force than the sharing of electrons between atoms, yet the hydrogen bonds are important in creating the structure of ice and causing it to float.
In addition to the lesson plan I think it is worth pondering some of the ways our world would be completely different if ice weren’t slightly less dense than water. How would that impact life in ponds? What about polar bears? What about the planet as a whole?
Periodic Videos offers some thoughts on the importance of the density of ice:
Hope you are having a great day exploring the world around you!