Molecule Profile: H2O - Water

Air Date: 01/11/2011
Source:
NBC Learn
Creator:
Beth Nissen
Air/Publish Date:
01/11/2011
Event Date:
01/11/2011
Resource Type:
Science Explainer
Copyright:
NBCUniversal Media, LLC.
Copyright Date:
2011
Clip Length:
00:04:46

This NBC Learn video "profiles" the H2O molecule -- its structure, polarity, cohesive and adhesive properties, and water's properties as a "universal" solvent.

Molecule Profile - H20 - Water

It might just be the most universally known fact in chemistry: the chemical formula for water - H2O.

A model of H2O doesn’t look like much – two small atoms of Hydrogen, the “H2” part of H2O, attached to one bigger atom of Oxygen, the “O” part of H2O. Kind of like a cartoon drawing of a teddy bear – and actually, water is kind of funny.

Fun Facts: Water – H2O – is the only natural substance on Earth found in all three common states of matter: liquid, solid, and gas, or vapor.

It’s also one of the only common substances that is less dense in solid form than in liquid form. And water can dissolve more substances than any other liquid.

Let’s focus on H2O in liquid form: What gives water its remarkable qualities and abilities?

It’s all in the molecule’s content and structure – not just what each H2O molecule is made of, but how the atoms are positioned, in what configuration and shape, and how they are bound together.

In water, just so you’ll know for later, the ‘H’s’ and ‘O’ are held together by covalent bonds – by sharing electrons.

H2O is a polar molecule: The same way our planet has North and South Poles on opposite sides, the H2O molecule has two poles on opposite sides. And like a magnet, H2O has one positive end and one negative end.

Thinking of that cartoon teddy bear again, the ‘chin’ side of the Oxygen atom has a slight negative electrical charge; the opposite side – the side with the two Hydrogen ‘ears’ – has a slight positive electrical charge.

This might just be the second most universally known bit of chemistry: opposites attract. The ‘positive’ Hydrogen side of every H2O molecule is going to attract, and be attracted to, the ‘negative’ Oxygen sides of other nearby H2O molecules, in all directions. More and more of them pull closer and closer together – until they’re like people in a hot, crowded dance club, packed so close together they can hardly move, but still turning and moving wildly.

Molecules that stay close to each other are called “cohesive” – and water is highly cohesive. A pentillion – even hextillion – of chaotically-moving, tightly-packed H2O molecules “cohere” to make a single raindrop.

As good as water molecules are at all this cohering and convening, they also form bonds with surfaces and molecules unlike themselves – a force called adhesion, as in adhesive. Pour the water out of a glass, and the inside of the glass is still wet: some H2O molecules stick – or adhere – to the silica molecules in the glass.

Being cohesive and adhesive is what makes water a (near) universal solvent. How? Take salt, or sodium chloride – sodium ions, abbreviated as Na-plus, and chloride ions, abbreviated as Cl-minus, in a crystal.

As soon as a salt crystal hits the water, it’s rushed by a molecular mob of H2O molecules that break it apart; separate the sodium and chloride ions – kind of a chemical divide and conquer.

Because sodium ions have a positive charge, each one is swarmed by H2O molecules flying at it with their negatively-charged Oxygen sides, completely surrounding the sodium ion, isolating it, carrying it off in a turbulent sea of H2O molecules.

The same thing happens in reverse to the chloride ions, which have a negative charge – each of those is surrounded and isolated by H2O molecules leading with their positively-charged hydrogen sides.

Each salt crystal is broken into tiny pieces – dissolved – by, and into, the water.

There’s much, much more to know about H2O and how it works to keep every living thing on the planet – and maybe other planets – alive.

Think of this video as a drop in the bucket.

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