PS-3.4 Classifying matter Pure substance - element compound Mixture - either homogeneous or heterogeneous

All matter in the universe can be classified (sorted) into two major categories, Pure substances and Mixtures. Pure substances can be either elements or compounds. Elements consist of a single kind of atom, they represent a "pure sort" and can be sorted out no more. Compounds consist of two or more elements chemically combined.

The elements in a compound can only be separated ( sorted) by using chemical means. One example of a chemical process that separates a compound into its constituent parts is shown here. 2H 2 O-->2H 2 + O 2. In this chemical change the compound water is separated the elements Hydrogen and Oxygen. Anytime a compound is separated into its parts, a chemical change must be carried out.

Mixtures can be subdivided into homogeneous mixtures and heterogeneous mixtures. The substances that are in a mixture are NOT chemically combined. As a result, the parts of a mixture can be separated from each other by physical methods such as physically picking out the different parts, filtering, distillation, or centrifuging.

The chart below shows how matter is classified.

ELEMENTS Are pure substances… They are made of only one kind of atom. They cannot be separated into anything simpler than single atoms. EXAMPLES: Gold, Silver, Sodium, Chlorine, Neon… all the elements on the periodic table!

COMPOUNDS Are pure substances Are made of more than one kind of atom chemically bonded to each other. They are made up of more than one kind of element. Chemical methods must be used to separate compounds into constituent elements. Examples: NaCl H 2 O KAlSi 3 O 8 MgSO 4

HOMOGENEOUS MIXTURES Physical combinations of two or more substances. Particles are atomic or molecular in size. Can be separated by physical methods such as distillation or chromatography. Examples: ALL solutions… like salt water, sugar dissolved in water, Iodine dissolved in alcohol…

HETEROGENEOUS MIXTURES Physical combinations of two or more substances. Often the particles are visible. Can be separated by physical means such as mechanical separation or filtering. EXAMPLES: Sand, salt mixed with pepper, dirt…

The End….. For now!