美國科學基金會(NSF)、美國科學教師協會(NSTA)及美國國家廣播公司(NBC)合作，為化學年製作了一系列教學單元，名為「今日化學(Chemistry Now)」，每周推出一單元，預計製作31單元。內容涵蓋日常生活中的化學，包含了21世界的先進化學。以下是第一單元：水的化學(Chemistry of Water)。
旁白：
Chemistry Now: 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 doesnt 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.
Its 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.
Lets focus on H2O in liquid form: What gives water its remarkable qualities and abilities?
Its all in the molecules 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 youll know for later, the Hs 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 theyre 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, its 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.
Theres 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.
學習單
國中：Density Comparison of Water and Ice
高中：Water is a Polar Molecule
‖ 下一單元：吉士堡化學--乳酪》
進一步參考資料：
1. NBC Learn- Chemistry now
2. NSTA Blog
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