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Water is the liquid of life.

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We drink it,

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we bathe in it,

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we farm,

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cook,

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and clean with it.

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It's the most abundant molecule in our bodies.

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In fact, every life form we know of

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would die without it.

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But most importantly, without water,

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we wouldn't have

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iced tea.

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Mmmm, iced tea.

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Why do these ice cubes float?

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If these were cubes of solid argon

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in a cup of liquid argon,

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they would sink.

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And the same goes for most other substances.

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But solid water, a.k.a. ice,

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is somehow less dense than liquid water.

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How's that possible?

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You already know that every water molecule

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is made up of two hydrogen atoms

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bonded to one oxygen atom.

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Let's look at a few of the molecules

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in a drop of water,

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and let's say the temperature is 25 degrees Celcius.

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The molecules are bending,

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stretching,

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spinning,

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and moving through space.

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Now, let's lower the temperature,

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which will reduce the amount of kinetic energy

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each of these molecules has

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so they'll bend, stretch, spin, and move less.

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And that means that on average,

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they'll take up less space.

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Now, you'd think that as the liquid water

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starts to freeze,

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the molecules would just pack together

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more and more closely,

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but that's not what happens.

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Water has a special kind

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of interaction between molecules

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that most other substances don't have,

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and it's called a hydrogen bond.

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Now, remember that in a covalent bond

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two electrons are shared,

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usually unequally,

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between atoms.

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In a hydrogen bond,

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a hydrogen atom is shared, also unequally,

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between atoms.

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One hydrogen bond looks like this.

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Two look like this.

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Here's three

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and four

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and five,

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six,

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seven,

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eight,

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nine,

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ten,

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eleven,

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twelve,

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I could go on.

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In a single drop of water,

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hydrogen bonds form extended networks

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between hundreds, thousands, millions,

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billions, trillions of molecules,

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and these bonds are constantly breaking and reforming.

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Now, back to our water as it cools down.

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Above 4 degrees Celcius,

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the kinetic energy of the water molecules

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keeps their interactions with each other short.

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Hydrogen bonds form and break

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like high school relationships,

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that is to say, quickly.

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But below 4 degrees,

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the kinetic energy of the water molecules

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starts to fall below the energy

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of the hydrogen bonds.

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So, hydrogen bonds form much more frequently

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than they break

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and beautiful structures start to emerge

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from the chaos.

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This is what solid water, ice,

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looks like on the molecular level.

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Notice that the ordered, hexagonal structure

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is less dense than the disordered structure

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of liquid water.

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And you know that if an object is less dense

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than the fluid it's in,

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it will float.

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So, ice floats on water,

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so what?

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Well, let's consider a world without floating ice.

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The coldest part of the ocean

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would be the pitch-black ocean floor,

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once frozen, always frozen.

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Forget lobster rolls

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since crustaceans would lose their habitats,

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or sushi since kelp forests wouldn't grow.

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What would Canadian kids do in winter

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without pond hockey or ice fishing?

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And forget James Cameron's Oscar

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because the Titanic totally would have made it.

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Say goodbye to the white polar ice caps

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reflecting sunlight

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that would otherwise bake the planet.

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In fact, forget the oceans as we know them,

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which at over 70% of the Earth's surface area,

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regulate the atmosphere of the whole planet.

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But worst of all,

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there would be no iced tea.

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Mmmmm, iced tea.