Science Chemistry Notes

Topics: Chemical element, Chemistry, Carbon dioxide Pages: 4 (427 words) Published: May 9, 2013
Elements, Mixtures and Compounds

An element is a pure substance made of one type of particle (atom). Particles can join up with other particles of the same type to form molecules. Examples: Hydrogen = H2 . This means there are two atoms of hydrogen joined together to form a molecule of hydrogen gas. Oxygen = O2, Nitrogen is H2, Chlorine is Cl2.

A compound is a pure substance of two or more elements chemically combined together in a set ratio. Example: Water = H20 this means there are always 2 atoms of Hydrogen and 1 atom of Oxygen in every molecule of water.


A Mixture is made of two or more substances mixed together, but NOT chemically joined. Mixtures can easily be separated by methods such as filtering, dissolving, evaporation and distillation. Example: Salt and sand, is made of particles of Sodium chloride (salt) and silicon dioxide (sand), these particles can be separated by dissolving the salt and then filtering the sand and salt solution. The salt solution passed through the filter and the insoluble sand stays behind in the filter paper. Pure salt can then be recovered by evaporating the water from the salt solution.

Web Link: Doc Brown’s Chemistry Clinic;

Examples of some compounds:

|Cartoon picture |Chemical compound |Elements present |Number of atoms of each element |Chemical formula | |[pic] |Water |Hydrogen |2 Hydrogen | | | | |Oxygen |1 Oxygen |H2O | |[pic] |Magnesium chloride |Magnesium |1 Magnesium | | | |...
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