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Geology LibreTexts

4.1: Unique properties of water

[This page could use image]

[Water is "bipolar"? Maybe meant to say water is considered a polar molecule]

[physical property- why does water make a good solvent?]

[what makes water unique to other substances? This is called "unique properties"? Perhaps mention that if water were not formed the way it were, life on earth would not have been the way it is, or even possible.]

[surface tension- should mention capillary action ]





Physical Properties of Water

Water is the only naturally occurring substance on Earth that can be found in three physical states: solid, liquid, and gas. In its solid form (ice), it is less dense than when it is in its liquid form (This is why ice floats in a glass of water).

The molecule has a cohesive property, allowing it to "stick" to other water molecules (Forming water "droplets" when molecules stick to one another, with the effect of gravity). It is also adhesive, meaning it "sticks" to other surrounding molecules in contact (An example of this being a water droplet on a blade of grass).

At sea level, water freezes at 32°F (0°C) to its solid state, and boils at 212°F (100°C) and becomes water vapor. 

Density: 1 gram/cubic centimeter (g/cc) at 39.2°F (4°C), and 0.95865 g/cc at 212°F (100°C)

Weight:  1,000 kilograms/cubic meter (kg/m³) at 32°F (0°C), and 993 kg/m³ at 212°F (100°C)

In its pure form, water does not conduct electricity. However, it can conduct water once it starts dissolving substances around it. Water is the best solvent out of all liquids--it can dissolve more substances than the rest.


Chemical Properties of Water

Water is made up of two hydrogen (H) atoms and an oxygen (O) atom. It is unique in that it is bipolar, where the molecule has a slightly positive charge on one side (where hydrogen atoms are attached), and slightly negative on the other (just oxygen). 

Since electrons are not equally distributed in a water, it is considered a polar molecule, despite it having the same number of protons and electrons. Also, because of its tetrahedral arrangement around the oxygen atom and the presence of lone pair electrons on the oxygen atom, water is considered to have a bent shape. 

One water molecule can connect with another molecule via a hydrogen bond (around 1/20 the strength of a covalent bond) between a hydrogen atom of one and an oxygen atom of the other. This hydrogen bond creates the surface tension in a group of water molecules. 

The pH of pure water is about 7 at room temperature (25°C or 77°F).



Each hydrogen atom in water is covalently bonded to the oxygen via a shared pair of electrons. Oxygen also has two unshared pairs of electrons, thus there are four pairs of electrons surrounding the oxygen atom, two pairs involved in covalent bonds with hydrogen, and two unshared pairs on the opposite side of the oxygen atom.

Water is a polar molecule means that there is an uneven distribution of electron density. Water has a partial negative charge near the oxygen atom due the unshared pairs of electrons,and partial positive charges near the hydrogen atoms. An electrostatic attraction between the partial positive charge near the hydrogen atoms and the partial negative charge near the oxygen results in the formation of a hydrogen bond. And the ability of ions and other molecules to dissolve in water is due to polarity. 

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