Why Do Ice Cubes Float Atop My Glass Of Water?

On a hot, sunny day, with the sticky, icky feeling of sweat and the echoing sounds of crickets, as you put some ice cubes on your glass of water, have you ever wondered why the ice is floating atop the water? Before unveiling the truth behind this phenomenon, let’s first talk about water. Water is a clear, flavorless, and odorless liquid that is essential to keeping life on Earth alive. It makes up between 60 and 75 percent of the human body and roughly 71 percent of the surface of the Earth.

In chemistry, water is defined as a substance composed of two slightly positively charged hydrogen atoms and one slightly negatively charged oxygen atom bonded with a covalent bond. When hydrogen bonds to oxygen, it forms an outstretched V shape with a positive and a negative side on each of its opposing sides. Due to its asymmetric charge distribution, water is identified as a polar molecule.

Now that we have learned what water is, let’s go back to our question: what makes ice float atop water? Usually, when liquid is frozen, its temperature decreases, and it becomes solid. It becomes denser as its molecules pack together tightly due to the decrease in kinetic energy. However, in the case of water, due to its structure, when frozen, its molecules push each other apart, decreasing its density.

To elaborate, when water freezes, the slightly positive hydrogen atoms of a water molecule are attracted to the slightly negative oxygen atom of another water molecule. When these bonds form during freezing, the extra hydrogen bonds increase the space between molecules, forming a lattice or crystalline structure, leading to a reduction in overall density.

At 4°C, the average density of water is 1 g/ml, whereas at 0°C, the average density of ice is 0.9 g/ml. Density refers to the characteristic property of a substance and is independent of its quantity. In the case of water and ice, ice, which is less dense, floats on water, which is more dense, hence answering the question of why ice floats atop water. (Contributed article)