1. Chapter 3 Atoms and Elements 3.4 Atomic Number and Mass Number 1 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

2. Atomic Number The atomic number is specific for each element is the same for all atoms of an element is equal to the number of protons in an atom appears above the symbol of an element in the Periodic Table Atomic Number Symbol 2 11 Na Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

3. Atomic Number = Protons in Atom For example, atomic number = number of protons: Atomic number H is 1; every H atom has one proton Atomic number of C is 6; every C atom has six protons Atomic number of Cu is 29; every Cu atom has 29 protons 3 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

4. Atomic Number = Protons in Atom 4 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

5. Atoms Are Neutral For neutral atoms, the net charge is zero. number of protons = number of electrons Aluminum has 13 protons and 13 electrons. The net (overall) charge is zero. 13 protons (13+) + 13 electrons (13 – ) = 0 5 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

6. Learning Check 6 Use the periodic table to fill in the atomic number, number of protons, and number of electrons for each of the following elements: ElementAtomic Number ProtonsElectrons N Zn S Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

7. Solution 7 Use the periodic table to fill in the atomic number, number of protons, and number of electrons for each of the following elements: ElementAtomic Number ProtonsElectrons N777 Zn30 S16 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

8. Mass Number 8 The mass number represents the number of particles in the nucleus is equal to the number of protons + the number of neutrons is always a whole number does not appear in the periodic table Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

9. Composition of Some Atoms of Different Elements 9 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

10. Study Tips: Protons and Neutrons Number of protons = atomic number Number of protons + neutrons = mass number Number of neutrons = mass number – atomic number Note: Mass number is given for specific isotopes only. 10 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

11. Learning Check An atom of lead (Pb) has a mass number of 207. A. How many protons are in the nucleus? B. How many neutrons are in the nucleus? C. How many electrons are in the atom? 11 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

12. Solution An atom of lead (Pb) has a mass number of 207. A. How many protons are in the nucleus? atomic number = 82; number protons = 82 B. How many neutrons are in the nucleus? mass number – number protons = number neutrons 207 – 82 = 125 neutrons 12 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

13. Solution An atom of lead (Pb) has a mass number of 207. C. How many electrons are in the atom? An atom is neutral, which means that the number of electrons is equal to the number of protons. An atom of Pb has 82 protons and 82 electrons. 13 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.