Introductory Concepts, Page 6

Mixture:

A combination of two or more substances in which the different substances maintain their own unique sets of properties. The substances are not chemically bonded to each other. Bonds may appear within individual components of the mixture, however. A mixture will not have its own unique formula. The substances in a mixture can be combined in any proportions. A mixture can usually be separated fairly easily into the individual substances with common physical processes. For example, salt water can be separated into salt and water by simple evaporation. Mixtures can be any combination of elements and/or compounds. Frequently, the phyical state of a substance may disappear when it becomes part of a mixture. For instance, a combination of salt and water, or salt water, appears to be a liquid, even though solid salt was used to prepare the solution.

Molecule:

The smallest characteristic particle of a compound. A single molecule will consist of two or more atoms, usually from different elements, that are chemically bonded. The individual molecule will still exhibit all the qualities that would be associated with a large sample of the compound.

Percent of Abundance:

Percent of Abundance refers to the quantity of a specific isotope that occurs in a natural sample of an element. It has been established that the distribution of the elements on Earth is such that a natural sample of an element will contain the same percent of abundance of a given isotope, no matter where the sample was obtained.

Physical Change:

A physical change is a change in the appearance of a substance. The original properties of the substance remain the same, but the substance looks different. Phase changes are some of the more common examples of physical changes. For instance, if ice melts into liquid water, then the product looks different from ice. It is still water, however. Physical change: H2O(solid) --> H2O(liquid)

Planetary Model:

The Planetary Model of the atom was developed by Rutherford. It was one of the first significant attempts to describe the atom as chemists know it today. The model describes the atom as being a small volume nucleus that concentrates the vast majority of the atom's mass. At a considerable distance from the nucleus the electrons were orbiting in a manner much like the way the planets orbit the sun. The majority of the volume of the atom was described as being empty space, or a vacuum. It is now known that there were some problems with this model, but at the time it was created, it was revolutionary.

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