Notes

Unit 2: Matter
Content Outline: Definition, Composition, and History of Matter (2.1)

I. Definition of Matter
A. Matter is anything that has mass and takes up space.
1. Examples of matter include: plants, animals, rocks, buildings, water, dust, and air.
2. Examples of things that are NOT matter include: different forms of energy,
emotions, thoughts, and dreams.

II. Composition of Matter
A. All matter is made up of tiny particles called atoms.
B. An atom is the smallest unit of matter that has all the properties of a given element.
C. It would take approximately 1 million atoms lined horizontally to equal the thickness of a human hair.

III. Early Concepts of the Atom
A. More than 2,400 years ago, Democritus, a Greek philosopher, believed that the universe was made
of empty space and tiny bits of stuff. He called these tiny bits of stuff “atoms.”
1. Democritus believed that different types of atoms existed for every type of
matter.
2. His ideas were not widely accepted during his lifetime. In fact, it was almost
2,100 years later before his ideas began to gain acceptance in the scientific community.
B. In the late 1700s, Antoine Lavoisier, a French chemist, conducted a series of experiments involving
chemical reactions, proving that matter could not be created or destroyed, it only changed form.
1. Lavoisier performed many experiments involving chemical reactions.
By using sealed flasks and precise balances, he was able to determine that
the masses of the substances before the chemical reaction were equal to the
masses of the new substances after the reaction.
2. From Lavoisier’s work came the law of conservation of matter, which states that matter is not
created or destroyed—it only changes form.