1. Physical Science 513 Unit 3 3.2 – Atoms and Elements

2. Lesson Objectives 6. 6. Demonstrate an understanding of Chapter 18 vocabulary words 7. 7. Describe the difference between an ion and an atom 8. 8. Explain how isotopes of a given element are different from each other 9. 9. Use a chemical symbol to calculate the number of protons, neutrons, and electrons

3. The Atom Definitions – –Atomic number: – –Mass number: – –Atomic mass: – –Ion : – –Isotope: The number of protons in an atom The number of protons + neutrons in an atom The average mass of an atom in a natural sample of the element An atom that has lost or gained one or more electrons so that it is no longer electrically neutral Atoms with the same number of protons but different number of neutrons

4. Chemical Symbols Example: Magnesium Mg Atomic Number (# of protons in nucleus)? – –12 – –Written in lower left hand corner of chemical symbol Mass Number (# of protons and neutrons)? – –24 – –Written in upper left hand corner of chemical symbol – –Can also be written after element name   Magnesium-24 or Mg-24 12 24

5. Isotopes Will isotopes of magnesium have different atomic numbers? – –No – –Why not? Will isotopes of magnesium have different mass numbers? – –Yes! – –Why? – –Example: Mg-24, Mg-25, and Mg-26 – –How many neutrons are in each of these?

6. Isotopes Isotopes are atoms of the same element that contain a different number of neutrons Hydrogen has 3 naturally occurring isotopes: – –Protium: 1p, 0n – –Deuterium: 1p, 1n – –Tritium: 1p, 2n Isotopes are identified by their mass number Protium has a mass number of 1 – –Can be written as hydrogen-1 – –Can also be written as H 1 1

7. Ions Will a magnesium ion have a different atomic number? – –No – –Why not? Will a magnesium ion have a different mass number? – –No – –Why not?

8. Ions Ion - an atom that has lost or gained one or more electrons No longer electrically neutral All that will change is the CHARGE Mg How many protons, neutrons, and electrons are represented above? 12 24 +2

9. Atomic Mass Periodic tables give atomic mass instead of mass number Atomic mass is the sum of all of the masses of the electrons, protons and neutrons The average atomic mass of the various isotopes of each element is shown on the periodic table What is the atomic mass for Magnesium? – –24.31