Early Atomic Theories

Directions Use the terms in the Word Bank to complete the paragraph. Write the terms on the lines.

Electrons were discovered by 1. _______________. He used a cathode-ray tube to prove that they existed. The tube contained a(n) 2. _______________ at each end. One was positively charged and called the 3. ______________. The other was negatively charged and called the 4. _______________. When electricity passed through the electrodes, a glowing beam called a cathode ray appeared. This ray could be deflected by a(n) 5. _______________. This meant that the beam must contain 6. _______________. It was proposed that this ray contained negatively charged particles that are in all elements. Later, 7. _______________ determined the charge and mass of an electron.

Directions Label each statement by the scientist who suggested it. Use D for Dalton or T for J. J. Thomson.

_________ 8. Atoms cannot be divided into smaller parts.

_________ 9. Chemical reactions occur when atoms separate, join, or rearrange.

_________ 10. All elements contain negatively charged particles.

_________ 11. All atoms of an element have identical properties.

_________ 12. A cathode ray contains matter, not energy.

Directions Answer each question on the lines. Use complete sentences.

13. Explain the difference between the atomic models of Dalton and Thomson.

14. What was being studied when electrons were discovered?

15. Why did the discovery of electrons mean that an atom must contain some positive charge?

© Pearson AGS Globe. Permission is granted to reproduce for classroom use only. Chemistry

Name Date Period Workbook Activity

Chapter 8, Lesson 1 48

Word Bankanode

cathode

electrode

J. J. Thomson

magnet

matter

Robert Millikan

08_662_Chem_TRL_WA.indd 1 3/28/06 4:06:33 PM