1. General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake 3.3 The Atom Chapter 3 Atoms and Elements © 2013 Pearson Education, Inc. Lectures

2. © 2013 Pearson Education, Inc. Chapter 3, Section 3 Dalton’s Atomic Theory 2 Dalton theorized that Atoms  are tiny particles of matter too small to see,  are able to combine with other atoms to make compounds, and  are similar to each other for each element and different from atoms of other elements. A chemical reaction is the rearrangement of atoms. Images of nickel atoms are produced when nickel is magnified millions of times by a scanning tunneling microscope (STM). This instrument generates an image of the atomic structure.

3. © 2013 Pearson Education, Inc. Chapter 3, Section 3 Subatomic Particles Atoms contain subatomic particles such as  Protons, which have a positive (+) charge;  electrons, which have a negative (–) charge; and  neutrons, which have no charge. Experiments show that like charges repel and unlike charges attract. 3

4. © 2013 Pearson Education, Inc. Chapter 3, Section 3 Rutherford’s Gold-Foil Experiment In Rutherford’s gold-foil experiment, positively charged particles were aimed at atoms of gold and  most went straight through the atoms, but  some were deflected only occasionally. Conclusion: There must be a small, dense, positively charged nucleus in the atom that deflects positive particles that come close. 4

5. © 2013 Pearson Education, Inc. Chapter 3, Section 3 Rutherford’s Gold-Foil Experiment 5 (a) Positive particles are aimed at a piece of gold foil. (b) Particles that come close to the atomic nuclei of gold are deflected from their straight path.

6. © 2013 Pearson Education, Inc. Chapter 3, Section 3 Structure of the Atom An atom consists of  a nucleus that contains protons and neutrons, and  electrons in a large, empty space around the nucleus. 6

7. © 2013 Pearson Education, Inc. Chapter 3, Section 3 Atomic Mass Scale On the atomic mass scale for subatomic particles, 1 atomic mass unit (amu) is defined as 1/12 of the mass of the carbon-12 atom. Therefore,  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, 0.00055 amu. 7

8. © 2013 Pearson Education, Inc. Chapter 3, Section 3 Particles in the Atom 8

9. © 2013 Pearson Education, Inc. Chapter 3, Section 3 Learning Check Identify each statement as describing a(n) proton, neutron, or electron. 1. _____________ 2. _____________ 3. _____________ 4. _____________ 9 Found outside the nucleus Has a positive charge Is neutral Found in the nucleus

10. © 2013 Pearson Education, Inc. Chapter 3, Section 3 Solution Identify each statement as describing a(n) proton, neutron, or electron. 1. electron 2. proton 3. neutron 4. protons, neutrons 10 Found outside the nucleus Has a positive charge Is neutral Found in the nucleus