1. Defining the Atom
4.1
The lab technician shown here is using a magnifying lens to examine a bacterial culture in a petri dish. When scientists cannot see the details of what they study, they try to obtain experimental data that help fill in the picture.

2. Early Models of the Atom
4.1
Early Models of the Atom
Early Models of the Atom
An atom is the smallest particle of an element that retains its identity in a chemical reaction.
Philosophers and scientists have proposed many ideas on the structure of atoms.

3. Early Models of the Atom
4.1
Early Models of the Atom
Democritus’s Atomic Philosophy
How did Democritus describe atoms?
Democritus

4. Early Models of the Atom
4.1
Early Models of the Atom
Democritus believed that atoms were indivisible and indestructible.
Democritus’s ideas were limited because they didn’t explain chemical behavior and they lacked experimental support.

5. Early Models of the Atom
4.1
Early Models of the Atom
Dalton’s Atomic Theory
How did John Dalton further Democritus’s ideas on atoms?

6. Early Models of the Atom
4.1
Early Models of the Atom
By using experimental methods, Dalton transformed Democritus’s ideas on atoms into a scientific theory.
The result was Dalton’s atomic theory.

7. Early Models of the Atom
4.1
Early Models of the Atom
All elements are composed of tiny indivisible particles called atoms.
This was later modified when it was discovered that atoms can be divided!
According to Dalton’s atomic theory, an element is composed of only one kind of atom, and a compound is composed of particles that are chemical combinations of different kinds of atoms. a) Atoms of element A are identical. b) Atoms of element B are identical, but differ from those of element A. c) Atoms of elements A and B can physically mix together. d) Atoms of elements A and B can chemically combine to form a compound. Interpreting Diagrams How does a mixture of atoms of different elements differ from a compound?

8. Early Models of the Atom
4.1
Early Models of the Atom
Atoms of the same element are identical. The atoms of any one element are different from those of any other element.
This was also modified later when it was discovered that all atoms of an element are not identical!
According to Dalton’s atomic theory, an element is composed of only one kind of atom, and a compound is composed of particles that are chemical combinations of different kinds of atoms. a) Atoms of element A are identical. b) Atoms of element B are identical, but differ from those of element A. c) Atoms of elements A and B can physically mix together. d) Atoms of elements A and B can chemically combine to form a compound. Interpreting Diagrams How does a mixture of atoms of different elements differ from a compound?

9. Early Models of the Atom
4.1
Early Models of the Atom
Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds.
According to Dalton’s atomic theory, an element is composed of only one kind of atom, and a compound is composed of particles that are chemical combinations of different kinds of atoms. a) Atoms of element A are identical. b) Atoms of element B are identical, but differ from those of element A. c) Atoms of elements A and B can physically mix together. d) Atoms of elements A and B can chemically combine to form a compound. Interpreting Diagrams How does a mixture of atoms of different elements differ from a compound?

10. Early Models of the Atom
4.1
Early Models of the Atom
Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element are never changed into atoms of another element in a chemical reaction.
According to Dalton’s atomic theory, an element is composed of only one kind of atom, and a compound is composed of particles that are chemical combinations of different kinds of atoms. a) Atoms of element A are identical. b) Atoms of element B are identical, but differ from those of element A. c) Atoms of elements A and B can physically mix together. d) Atoms of elements A and B can chemically combine to form a compound. Interpreting Diagrams How does a mixture of atoms of different elements differ from a compound?
Scientists used a scanning tunneling microscope to generate this image of iron atoms, shown in blue. The radius of this circle of atoms is just 7.13 × 10-9 m.

11. 4.1 Section Quiz
1. The ancient Greek philosopher credited with suggesting all matter is made of indivisible atoms is
Plato.
Aristotle.
Democritus.
Socrates.
ANS: C PTS: 1 REF: p. 101 OBJ: 4.1.1

12. 2. Dalton's atomic theory improved earlier atomic theory by
4.1 Section Quiz
2. Dalton's atomic theory improved earlier atomic theory by
teaching that all matter is composed of tiny particles called atoms.
theorizing that all atoms of the same element are identical.
using experimental methods to establish a scientific theory.
not relating atoms to chemical change.
ANS: C PTS: 1 REF: p. 102 OBJ: 4.1.2