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General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake Chapter 3 Atoms and Elements 3.3 The Atom © 2013 Pearson Education, Inc. Lectures Dalton’s Atomic Theory 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. © 2013 Pearson Education, Inc. 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. Chapter 3, Section 3 2 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. © 2013 Pearson Education, Inc. Chapter 3, Section 3 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. © 2013 Pearson Education, Inc. Chapter 3, Section 3 4 Rutherford’s Gold-Foil Experiment (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. © 2013 Pearson Education, Inc. Chapter 3, Section 3 5 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. © 2013 Pearson Education, Inc. Chapter 3, Section 3 6 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. © 2013 Pearson Education, Inc. Chapter 3, Section 3 7 Particles in the Atom © 2013 Pearson Education, Inc. Chapter 3, Section 3 8 Learning Check Identify each statement as describing a(n) proton, neutron, or electron. 1. _____________ Found outside the nucleus 2. _____________ Has a positive charge 3. _____________ Is neutral 4. _____________ Found in the nucleus © 2013 Pearson Education, Inc. Chapter 3, Section 3 9 Solution Identify each statement as describing a(n) proton, neutron, or electron. 1. electron Found outside the nucleus 2. proton Has a positive charge 3. neutron Is neutral 4. protons, neutrons Found in the nucleus © 2013 Pearson Education, Inc. Chapter 3, Section 3 10