MATTER AND ENERGY

2.4 - Classification of Matter

2.4.1 - Pure Substances

Water

When two hydrogen atoms combines with an oxygen atom, a compound called water is formed. The picture on the left is a molecule of water. Every unit of water has two hydrogen atoms and one oxygen atom. This unit has a 'fixed proportion' of hydrogen atoms to oxygen atoms. We can refer to this fixed proportion as: water is 11% hydrogen and 89% oxygen by mass OR water is made up of 2 hydrogen atoms and 1 oxygen atom Inherited by this fixed proportion of hydrogen and oxygen unit are all the physical and chemical properties of water as we know it. Some physical and chemical properties of water (which you may or may not know) include: melting point is 0oC boiling point is 100oC an excellent solvent for ionic compounds capable of forming hydrogen bonds with other water molecules solid form of water is less dense than liquid water

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