First are those characteristics that can be detected by the five senses; seeing, hearing , smelling, tasting, and feeling. It is easy to see that aluminum is shiny and carbon is dull black. You can determine the difference by the odor of a flower versus rotting meat. The taste of sodium chloride (table salt) and the feel of a metal are both very distinctive.

Second are those characteristics that can be measured in the laboratory by instruments. Things such as melting point, boiling point and density can easily be measured without damaging the substance.

Changes that alter the physical form of a substance without changing its chemical structure are called Physical Changes. The boiling of water or the melting of ice are examples of physical changes. The dissolving of sugar into a glass of tea changes the form of the sugar but does not change the chemical structure. Physical changes involve changing the substance between states of matter.