1. 1 Chapter 2 Atoms and Molecules 2.2 Inside the Atom Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

2. 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 © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

3. 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 © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

4. 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. 5 Rutherford’s Gold-Foil Experiment Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

6. 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 © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

7. 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, 0.000549 amu.

8. 8 Particles in the Atom

9. 9 Learning Check Identify each statement as describing a 1) proton 2) neutron3) electron A. found outside the nucleus B. has a positive charge C. is neutral D. found in the nucleus

10. 10 Solution Identify each statement as describing a 1) proton 2) neutron3) electron A. 3 found outside the nucleus B. 1 has a positive charge C. 2 is neutral D. 1, 2 found in the nucleus