WATER

In distilled water the majority of the atoms are covalently bonded.

A very small number of water molecules are dissociated. These form ions:

ionized water

When a solute is dissolved in water it can cause more water molecules to dissociate into ions. Some of the H⁺ ions are attracted to water molecules forming H₃0⁺ ions

the hydronium ion

Also, water molecules have weak bonds of attraction between them. These are called hydrogen bonds.

Hydrogen bonds between molecules of water

A sample of water is in constant movement. Dissociated ions rejoin to form molecules and vice versa. Weak hydrogen bonds between the oxygen atom in one molecule of water and an hydrogen atom in another molecule break and reform.

These properties of water are extremely important. To understand why, let’s compare the water molecule to the hydrogen sulphide molecule.

Hydrogen sulphide molecule

Hydrogen sulphide is a larger molecule than water but it does not form hydrogen bonds. Hydrogen sulphide is a gas at room temperature and pressure but water is a liquid. Without hydrogen bonds water would also be a gas at room temperature and pressure. It is the hydrogen bonds and the dynamic nature of water that allowed life to evolve on the planet Earth.

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