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Chapter 4 “Atomic Structure” Section 4.1 Defining the Atom OBJECTIVES: Democritus’s ideas about atoms. Describe Section 4.1 Defining the Atom OBJECTIVES: Explain theory. Dalton’s atomic Ancient Philosophy Who: Aristotle, Democritus When: More than 2000 years ago Where: Greece What: Aristotle believed in 4 elements: Earth, Air, Fire, and Water. Democritus believed that matter was made of small particles he named “atoms”. Why: Aristotle and Democritus used observation and inference to explain the existence of everything. Section 4.1 Defining the Atom The Greek philosopher Democritus (460 B.C. – 370 B.C.) was among the first to suggest the existence of atoms (from the Greek word “atomos”) He believed that atoms were indivisible and indestructible His ideas did agree with later scientific theory, but did not explain chemical behavior, and was not based on the scientific method – but just philosophy Democritus Aristotle Alchemists Who: European Scientists When: 800 – 900 years ago Where: Europe What: Their work developed into what is now modern chemistry. Why: Trying to change ordinary materials into gold. Alchemic Symbols Particle Theory Who: John Dalton When: 1808 Where: England What: Described atoms as tiny particles that could not be divided. Thought each element was made of its own kind of atom. Why: Building on the ideas of Democritus in ancient Greece. John Dalton Particle (Atomic) Theory 1. All elements are composed of tiny indivisible particles called atoms 2. Atoms of same elements are identical. Atoms from one element are different from atoms of a different element. 3. Atoms of different elements can physically mix together or can be chemically combine to form compounds. 4. Chemical reactions occur when atoms are separated, joined, or rearranged. However, atoms of an element never changes into atoms of another element as a result of the chemical reaction. (p102 textbook) Sizing up the Atom Elements are able to be subdivided into smaller and smaller particles – these are the atoms, and they still have properties of that element If you could line up 100,000,000 copper atoms in a single file, they would be approximately 1 cm long Despite their small size, individual atoms are observable with instruments such as scanning tunneling (electron) microscopes