Elements, Compounds, and Mixtures
- 5.0 Recognize that there are more than 100 elements that combine in
a multitude of ways to produce compounds that make up all the living and
nonlicving things that we encounter.
- 6.0 Differentiate between an atom (the smalles unit of an element that
maintains the characteristics of the element) and a molecule (the smallest
unit of a compound that maintains the characteristics of that compound).
- 7.0 Give basic examples of elements and compounds.
- 8.0 Differentiate between mixtures and pure substances.
- 9.0 Recognize that a substance (element or compound) has a melting point
and a boiling point, both of which are independent of the amount of the sample.
- 10.0 Differentiate between physical changes and chemical changes.
planetary systems with stars
Atoms and Molecules
An atom is the smallest unit of an element that maintains the characteristics of that element.
A molecule is the smallest unit of a compound that maintains the characteristics of that compound.
A MIXTURE is a combination of two or more substances that are not chemically united and do not exist in fixed proportions to each other.
Melting and Boiling Points
Melting Point: As solid matter is heated it eventually melts or changes into a liquid state at the melting point.
Ice (a solid form of water) melts at 0 oC and changes to the liquid state.
Boiling Point: As the liquid matter is heated further it eventually boils or vaporizes into a gas at the boiling point.
Liquid water boils and changes into a gas, usually called steam or water vapor at 100 oC. In all three states the same molecules of water (H2O) are present.
Physical and Chemical Change
A chemical change alters the composition of the original matter. Different elements or compounds are present at the end of the chemical change. The atoms in compounds are rearranged to make new and different compounds.
A physical change takes place without any changes in molecular composition. The same element or compound is present before and after the change. The same molecule is present through out the changes. Physical changes are related to physical properties since some measurements require that changes be made.