Why Does Ice Float?

Why Does Ice Float?

            A lot of substances in the world can be formed into three different states, solid, liquid, and gas.  Normally each state the substance is in changes its density with solid being the most dense, then liquid, then gas.  Density is the degree of compactness in a substance, water for example has a density of about 1g/cm³, anything with a larger density will sink, and anything with a smaller density will float.

            Ice is the solid form of water, so why does it float?

            Theoretically ice should sink, it is the solid form for water, and it technically should have a larger density.  When tossing rocks into water they sink, the rocks are able to displace the water around it and sink to the bottom. According to Anne Marie Helmenstine, who has her doctorate in philosophy in biomedical sciences from the University of Tennessee at Knoxville with a bachelor of arts degrees in physics and mathematics with a minor in chemistry from Hastings College in Nebraska, in her article “Why Does Ice Float? Ice and the Density of Water”.

            Dr. Helmenstine explains that water becomes the most dense at about 40^o Fahrenheit and as it gets colder and starts to become frozen, it actually loses its density.

            Wouldn’t it make sense that when water is frozen its particles would stop moving and stack closer together? That doesn’t happen because of Hydrogen Bonding.  Dr. Helmenstine explained that hydrogen bonding is when a positively charged hydrogen atom from a water molecule meets a negatively charged oxygen atom from a neighboring water molecule and they form a bond.

            According to George Zaidan, a science communicator who created, wrote, and hosted National Geographic’s webseries Ingredients; and co-wrote and directed MIT’s webseries Science Out Loud, also, he has several viral TED-Ed videos, in one of his TED-Ed videos he says that Hydrogen bonds form all the time even in waters liquid states.

            Zaiden says that in liquid form however the hydrogen bonds form and break every second with the water molecules moving around forming a new bond each time.  This causes the molecules to seem more compact because they are always moving and connecting with each other.

            Zaiden continues by showing a diagram in the TED video that shows the difference between the liquid molecules and solid ones.  The liquid molecules move around, attach and detach in a more compact way, while when ice is formed the molecules attach forming a hexagonal spacious look, causing there to be more molecules per cm³ in the liquid form than the solid form.

            Dr. Helmenstine explains that in conclusion Ice floats because it is about 9% less dense than water, or ice takes up 9% more space than water.  The heavier water displaces the lighter ice causing it to float to the top.