Download Dalton, Plum Pudding, and Rutherford`s Atomic Theories (Models) 9

Dalton, Plum Pudding, and Rutherford’s Atomic Theories (Models) 9/2/10
Objectives
1. To learn about Dalton’s theory of atoms
2. To understand and illustrate the Law of constant composition
3. To learn how a formula describes a compound’s composition
4. To learn about the internal parts of an atom
5. To learn about The Plum Pudding model of an atom
6. To understand Rutherford’s experiment and learn about his atomic theory
7. To describe some important features of subatomic particles
8. To learn about the terms isotope, atomic number, and mass number
9. To understand the use of the symbol
to describe a given atom
Law of Constant Composition
• A given compound always contains the same proportion by mass of the elements
of which it is composed.
• This law (and others) led Dalton to compose his Atomic Theory which states:
• All elements are composed of indivisible particles called atoms.
• All atoms of a given element are identical.
• Atoms of different elements are different.
• Compounds consist of the atoms of different elements.
• Atoms are not created or destroyed in a chemical reaction; they are only
rearranged.
• A given compound always contains the same proportion by mass of the elements
of which it is composed.
More Atomic Theories
• Experiments by J.J. Thomson with a cathode ray tube showed that atoms contain
electrons. He came up with:
The Plum Pudding Model
• A spherical cloud of positive with negative particles embedded in it
•
Rutherford’s Gold Foil Experiment
• Alpha particles (small, positive particles) were aimed at a thin piece of metal
(gold) foil.
•
•
If the Plum pudding model was accurate, the left diagram above would have
illustrated the results.
However, the results actually support a new atomic theory, with a small dense
nucleus in the center of an atom, as shown on the right diagram above.
•
Rutherford’s Atomic Theory and Subatomic Particles
• Ernest Rutherford showed that atoms have internal structure.
– The nucleus, which is at the center of the atom, contains protons
(positively charged) and neutrons (uncharged).
– Electrons move around the nucleus, similar to planets moving around the
sun.
– The relative mass and charges of the three subatomic particles is
summarized below.
•
A particular isotope is represented by the symbol
.