Compounds and Mixtures

Compounds:

A compound is a substance which contains 2 or more elements chemically combined.
e.g. magnesium+oxygen= magnesium oxide(compound). It has very different properties from the elements that form it. 
Mixtures and Compounds

(element)+(element)-> compound
e.g. sodium+chlorine-> sodium chloride
(element)+(compound)-> compound
e.g. oxygen+ carbonmonoxide-> carbon dioxide
(compound)+(compound)-> compound
e.g. Carbon dioxide+water-> carbonic acid


Properties of a compound:

• properties of a compound are different from the properties of its constituent elements.
• compounds can be broken down into simpler substances by chemical methods
• the different elements in a compound are joined together in a fixed proportion by mass. e.g. water is a compound made only by joining together 2 atoms of hydrogen to one atom of oxygen. The ration of hydrogen atoms to oxygen atoms is always 2:1.

Chemical formula of a Compound

- a compound can be represented by a chemical formula. It is written by putting together the chemical symbols of the elements that make up the compound.

Chemical formula has the types of atoms present in the compound and ratio of different atoms present in the compound.

Decomposition of Compounds 

-Heat can be used to form compounds. Heat can also be used to break down compounds into elements/ simpler compounds.(Thermal decomposition)

-Besides heat, compounds can also be broken down by electricity into simpler substances.

Mixtures


- A mixture is formed when 2 or more substances are added together without chemical bonds being formed. Examples of mixtures include muddy water and air. Air is made up of of gases such as nitrogen and oxygen, etc.
-Constituents of a mixture may be all elements, all compounds or combination of elements and compounds. Substances in mixture can be solids, liquids or gases.

• components of a mixture can be separated by physical methods. e.g. filtration, distillation or chromatography.
• chemical properties of a mixture are the same as those of its components.
• no chemical reaction takes place when a mixture is formed.-little or no energy change
• components of mixture can be mixed in any proportion. (proportion of constituents in a mixture are not fixed)

Example: Alloys

-> example of a mixture.(mixture of metals with other elements)-usually metals but sometimes non-metals like carbon.

-> widely-used- tend to be stronger than pure metals