Compounds and Mixtures

In the field of chemistry, the chemical form of matter, whether solid, liquid or gas, can be classified as an element, compound or mixture. The word substance can refer to an element or a compound but not a mixture. The word matter can refer to substance, element, mixture or compound.

An atom is the smallest unit of a chemical element. An element may consist of one or more than one atom, but only one kind of atom. However, these identical atoms may combine to make molecules. Elements cannot be broken down into any simpler form of matter. Some elements occur in nature only. Some occur in nature but may also be produced in a laboratory. It is thought that there may be more elements that are known today. These would probably exist for only a short amount of time because they are radioactive. They would decompose into another element. Its atoms would be smaller. Over ninety naturally occurring elements exist. There are also some man-made elements.

A mixture consists of one or more different elements combined physically. These can then be separated physically also. They retain many of the properties of the original elements. There are six different types of mixtures. The elements can be separated by physical means, such as filtration (using a coffee filter), decantation (letting the sand in water settle to the bottom) or evaporation. Sunlight or warm heat can be used for evaporation.

Homogeneous mixtures have all the contributing substances distributed evenly throughout the mixture. An example is vinegar. A heterogeneous mixture has substances which are not evenly distributed throughout the mixture. An example would be oil and water when mixed. A solution is a type of homogeneous mixture where one substance is dissolved in another. One substance is called the solute. This is dissolved in another substance called the solvent. Salt is dissolved in water and becomes salt water.

The fourth type of mixture is a suspension. This is a liquid heterogeneous mixture which contains some solid particles which can eventually sink down as sediment in a container. Mixing sand with water is an example. The sand will sink to the bottom after a short period. The fifth type of mixture is a colloid. This is a mixture where the particles of the solute are very small. It is a heterogeneous mixture where the particles are smaller than those in a suspension but greater than those in a solution. Milk is an example of a colloid. The last type of mixture is an alloy. An alloy is a mixture where the element or elements are metals. Steel and bronze are examples of alloys. Two or more types of metal are mixed together.

A compound consists of two or more elements put together by chemical means. Its molecules are all identical. They can only be separated by chemical means also. The compound always contains the same ratio of atoms. A compound has different properties than each individual element, unlike a mixture. A molecule is the smallest part of a compound which has the properties of the compound. A chemical formula can represent a compound.

Water is a compound. It is formed from hydrogen and oxygen. H stands for the element hydrogen. O stands for the element oxygen. Two atoms of hydrogen join with one atom of oxygen to form the compound H2O. Water has different properties than its two elements, hydrogen, and oxygen. An eggshell is made from a calcium carbonate compound. There are more compounds of carbon than any other element. The carbon compound in all living things is called an organic compound.

A: Molecule
B: Carbon
C: Atom
D: Mixture

A: All the atoms of an element must be identical.
B: Compounds may be separated by physical means.
C: Mixtures may not be separated.
D: Homogeneous is one type of compound.

A: Organic carbon is found in all non-living things.
B: A compound has different properties from each of its elements.
C: Water is made from the elements of carbon and oxygen.
D: Hydrogen compounds are the most common in the world.

A: Homogeneous
B: Colloid
C: Suspension
D: Heterogeneous

A: A carbon compound
B: A mixture of metals
C: A colloid
D: All water compounds

A: Colloid
B: Suspension
C: Solution
D: Homogeneous

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