El agua

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PROPERTIES OF WATER

Covalent bonds form when atoms share electrons. Sometimes this sharing is not equal and leads to the formation of partial charges on molecules.

Consider water. The electron associated with the hydrogen atom tends to spend more time orbiting the oxygen atom. This doesn't result in the loss of electrons like we saw in ions. It's just unequally shared. Therefore:

• Oxygen has a partly "extra" electron making it slightly negative.
• Each hydrogen has "lost" an electron making it partly positive.

Hydrogen Bonds in Water

We know that opposite charges attract, even weak opposites. This weak attraction between the partly positive and partly negative parts of water allows for the formation of hydrogen bonds.

Pictured below, you can see the partial charges on a water molecule and how they then form hydrogen bonds with other water molecules.

  

  

Polar and Nonpolar Substances

Since the water has opposite charges on different parts of the same molecule we call it Polar.

• A Polar substance has charges that can interact with the charges in water. Therefore Polar molecules are said to be Hydrophilic too (water loving).

• A Nonpolar substance then lacks any charges and will not be able to interact with water. Nonpolar molecules are said to be Hydrophobic (water hating).

Since water molecules are attracted to each other by hydrogen bonds, water exhibits a property called surface tension. Water molecules will attract to each other to form a film and will resist any attempt to separate them. This is easily seen when water beads up on a hard surface to form something like a sphere.

Saturation

Even though the hydrogen bonds in water are considered very weak, they can be strong when in numbers. In some cases, weaker bonds can overcome stronger bonds

(salt or sugar dissolves in water)

Saturation occurs when there are no longer enough hydrogen bonds to overcome the stronger ionic bonds. This is why you can only dissolve a certain amount of sugar in iced tea. Eventually the water will not be able to interfere with the ionic bonds holding the crystals together.

In fact, if enough individual ions are added to water they will eventually form a crystal shape and fall to the bottom of the container.

Fuente: http://www.personal.psu.edu/staff/m/b/mbt102/bisci4online/chemistry/chemistry3.htm