Lecture for Wednesday, August 27th

Definitions of Chemistry

Chemistry deals with the properties of materials and the changes these materials undergo. (DLB, 7th Ed., Prentice-Hall)

Chemistry is a physical science that deals with the composition, structure and properties of substances and the reactions they undergo. As a science, chemistry involves the intuitive and creative application of knowledge gained from experiment observation and theoretical descriptions.

Anything that bites or scratches is biology
Anything that stinks or pops is chemistry
Anything that does not work is physics

Definition of Matter

The two distinguishing characteristics of matter is that matter is classified as anything that has mass and occupies space.

Composition of Matter

Pure substances
- matter that has a fixed composition and distinct physical and chemical properties.
  - Atoms
    Matter is composed of atoms.
    - Atoms are the smallest particles of an element that retain the chemical properties of the element.
    - An element is an example of matter which consists of only one kind of atom, either individually or combined into larger units.
- Molecules
  - Molecules are units of matter consisting of two or more atoms combined in a definite ratio.
    
    When the atoms are the same in a molecule the substance is an element.
    
    When the atoms are different the substance is considered a compound.

Mixtures

combinations of two or more substances where each substances retains its chemical identity (its physical and chemical properties).
- heterogeneous mixtures do not have the same composition, properties or appearance.
- homogeneous mixtures do have the same composition, properties or appearance.

Diagram of an STM instrument.
Some STM Images of atoms and or molecules.

Here is another site with STM images.

Characterization of Matter

To characterize matter we use physical and chemical properties.

Physical properties are properties that can be measured and observed without changing the identity of the substance.

State(gas, liquid and solid)
Color
Melting Point (Important to note that a change in phase, which occurs at the boiling point or melting point of a substance does not necessarily mean a chemical change has occurred.)
Boiling Point
Density
Texture
Hardness
Also important are

Mass
Volume
but these properties have less to do with distinguishing between substances.

Examples of physical properties of matter.