1. Physical Science: Chapter 4
Section 1
Development of Atomic Theory

2. Physical Science: Atomic Models
Today, we know that an ______ is the smallest unit of a particular ______________.
But, people haven’t always thought that.

3. Physical Science: Atomic Models
______________________
The first person to propose this idea was the Greek scientist _______________around 400 B.C.
Democritus said that everything
was made of very
small, indivisible
___________he called
“_____________.”

4. Physical Science: Atomic Models
II. _____________
Based on his ___________with
gases, in 1808, ____________,
an English chemist,
developed the first
“modern”________
about atoms.

5. Dalton’s Theory A Summary of Dalton’s Atomic Theory:
An element is composed of tiny, indivisible, indestructible ___________called atoms.
All atoms of an element are __________and have the same ______________.
Atoms of different elements combine to form __________________.
Compounds contain atoms in small ______________ ratios.
Atoms can combine in more than one ratio to form ___________________compounds.

6. Dalton’s Atomic Theory
The first two parts of Dalton’s theory were later proven ________________.
We will see this later.
Proposals 3, 4, and 5 are ___________________.
____________theory was an important step in the further development of _____________theory.
A __________model of the atom:

7. Physical Science: Atomic Models
III. _________________
Today, we know that there are particles even ________than atoms (________, _________and _________) that are ____________atoms.

8. Subatomic Particles
About years after Dalton’s proposal, evidence was seen that atoms ______________.
Two subatomic particles were discovered.
negatively charged _______________, e–
positively charge ___________________, p+
An electron has a relative charge of -1, and a proton has a relative charge of +1.

9. Thomson’s Work
Famous Experiment- Cathode Ray Tube
Chapter 5

10. Physical Science: Atomic Models
_______________concluded that particles _________than atoms existed and that they had _____________electric charges.
The term ____________is used for these negative charges.

11. Thomson’s Model of the Atom
J.J. Thomson proposed a ________model of the atom around 1900.
Thomson proposed that the _____________were distributed evenly throughout a homogeneous ___________of positive charge.
This was called the “_________ ____________” model of the atom Think of a chocolate chip cookie.

12. Rutherford’s Gold Foil Experiment
___________student fired alpha particles at thin _____ ________. If the “plum pudding” model of the atom was correct, α-particles should _______________ ____________________.
However, some of the alpha particles were ____________________.

13. Explanation of Scattering
Most of the alpha particles passed through the foil because an atom is largely _______________.
At the center of an atom is the _______________, which contains the atom’s ____________.
The α-particles that bounced backwards did so after striking the _____________.

14. Rutherford's ____________Model of the Atom
____________________proposed a new model of the atom:
The negatively charged _______are distributed around a positively charged _________.
An atom has a diameter of about 1 × 10-8 cm and the nucleus has a diameter of about 1 × cm.
If an atom were the size of the Superdome, the nucleus would be the size of a marble.

15. Subatomic Particles Revisited
Based on the heaviness of the nucleus, Rutherford ___________that it must contain _________particles in addition to ________.
_______, n0, were discovered about 30 years later by _____________. A neutron is about the same ___as a proton without any charge.

16. Summary of Models
__________- Philosophical (thought) idea of the atom. The word “atom” originated in Greek.
_____________- Experiment and Postulates about the existence of atoms- Picture as a marble or solid sphere that makes up matter (a brick in a wall).
_______________- Idea of electron- Small with negative charge- Cathode ray tube experiment- “Plum Pudding Model”
_______________- Nucleus with positive charge (Protons/ Neutron comes later)- Gold foil experiment- Nucleus very dense with much of atom as “empty space.”- “Nuclear” Model