Chemistry 111

Chemistry is the study of matter and how it transforms. In order to discuss matter, it is important to develop a language which we can use to discuss the topic. However, in order to describe samples of matter, let’s first think about changes.

Change
This can be any sort of transformation in which some or all of the properties of the sample are altered.
Physical Change		Chemical Change
Any change that does not involve the breaking or formation of chemical bonds.		Any change that does involve the breaking or formation of chemical bonds.

Some Examples

Change	Classification
Separating morbles into piles sorted by color	Physical Change
Cutting a piece of paper with scissors	Physical Change
Burning a piece of paper with a match	Chemical Change
Precipitating Ag+(aq) ions with HCl(aq)	Chemical Change
Filtering AgCl(s) from a slurry	Physical Change
Recrystalizing NaCl(s) from a solution of Na+(aq) and Cl-(aq) ions	??? Change

Once we understand how to think about the transformations of matter, it is possible to consider how to classify samples of matter based on how the sample can be separated into simpler (or component) samples of matter.

Sample
This can be any sample of matter.
Mixture		Pure Substance
A sample of matter than can be separated into component samples using only purely physical methods is defined as a mixture.		A sample of matter that can not be decomposed into component samples of matter using purely physical methods is defined as a pure substance. It is possible that a pure substance can not be separated into compoent materials at all, however!
Heterogeneous Mixture	Homogeneous Mixture	Compound	Element
A heterogeneous mixture is oen in which the composition is not uniform. And so, a sub-sample of a heterogeneous mixture may have a different composition than an different sub sample.	A homogeneous misture is one with a uniform composition throughout. As such, an sub-sample of a homogeneous mixture has exactly the same composition as any other sub-sample.	A compound is a pure substance that consists of more than one element. As such, it can be decomposed into simpler components using chemical methods.	An element can not be decomposed into simpler atoms using any normal chemical methods.