1. 1 Chapter 4 Atoms and Elements 4.3 The Atom Basic Chemistry Copyright © 2011 Pearson Education, Inc.

2. 2 Dalton’s Atomic Theory Atoms are tiny particles of matter of each element are similar and different from atoms of other elements of two or more different elements combine to form compounds are not created or destroyed in a reaction Basic Chemistry Copyright © 2011 Pearson Education, Inc.

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 Basic Chemistry Copyright © 2011 Pearson Education, Inc. Like charges repel, and unlike charges attract.

4. Thomsen’s “Plum Pudding” Model of the Atom J.J.Thomsen discovered that cathode rays were streams of small negatively charged particles called electrons proposed the “plum pudding” model of an atom in which protons and electrons were distributed throughout the atom 4 Basic Chemistry Copyright © 2011 Pearson Education, Inc.

5. 5 Rutherford’s Gold-Foil Experiment In Rutherford’s gold-foil experiment, positively charged particles were aimed at atoms of gold most went straight through the foil only a few were deflected conclusion: There must be a small, dense, positively charged nucleus in the atom that deflects positive particles that come close Basic Chemistry Copyright © 2011 Pearson Education, Inc.

6. 6 Rutherford’s Gold-Foil Experiment Basic Chemistry Copyright © 2011 Pearson Education, Inc. Positive particles moving toward atoms of gold are deflected from their path by the positive charges of the gold atoms.

7. 7 Structure of the Atom An atom consists of a nucleus that contains protons and neutrons of electrons in the large empty space around the nucleus Basic Chemistry Copyright © 2011 Pearson Education, Inc. In an atom, the protons and neutrons are in the nucleus, whereas the electrons are contained in the large space outside the nucleus.

8. 8 Atomic Mass Scale On the atomic mass scale for subatomic particles, 1 atomic mass unit (amu) is equal to 1/12 of the mass of the carbon-12 atom a proton has a mass of 1.007 amu a neutron has a mass of about 1.008 amu an electron has a very small mass of 0.00055 amu Basic Chemistry Copyright © 2011 Pearson Education, Inc.

9. 9 Particles in the Atom Basic Chemistry Copyright © 2011 Pearson Education, Inc.