1. Chapter 3 Atoms and Elements
3.4
The Atom
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Publishing as Benjamin Cummings

2. Dalton’s Atomic Theory
In Dalton’s Atomic Theory, atoms
are tiny particles of matter.
of an element are similar and different from other elements.
of two or more different elements combine to form compounds.
are rearranged to form new combinations in a chemical reaction.
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

3. Subatomic Particles Atoms contains subatomic particles,
protons have a positive (+) charge.
electrons have a negative (-) charge.
like charges repel and unlike charges attract.
neutrons are neutral.
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

4. Rutherford’s Gold-Foil Experiment
In Rutherford’s gold-foil experiment, positively
charged particles
were aimed at atoms of gold.
mostly went straight through the atoms.
were deflected only occasionally.
Conclusion:
There must be a small, dense, positively charged nucleus in the atom that deflects positive particles that come close.

5. Rutherford’s Gold-Foil Experiment
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Publishing as Benjamin Cummings

6. Structure of the Atom An atom consists
of a nucleus that contains protons and neutrons.
of electrons in a large empty space around the nucleus.
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

7. Atomic Mass Scale On the atomic mass scale for subatomic particles,
1 atomic mass unit (amu) has a mass equal to 1/12 of the mass of the carbon-12 atom.
a proton has a mass of about 1 (1.007) amu.
a neutron has a mass of about 1 (1.008) amu.
an electron has a very small mass, amu.

8. Particles in the Atom

9. Learning Check Identify each statement as describing a
1) proton 2) neutron 3) electron
A. found outside the nucleus
B. has a positive charge
C. is neutral
D. found in the nucleus

10. Solution Identify each statement as describing a
1) proton 2) neutron 3) electron
A found outside the nucleus
B has a positive charge
C is neutral
D. 1, 2 found in the nucleus