1. Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 3 How Atoms Differ

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 3 The Atom Objectives Describe the size of an atom. Name the parts of an atom. State how atoms of different elements differ. State how isotopes differ. Calculate atomic masses. Describe the role of electrons in an atom. Chapter 4

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 3 The Atom How Small Is an Atom? Scientists know that aluminum is made of average- sized atoms. An aluminum atom has a diameter of about 0.00000003 cm. Chapter 4

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 3 The Atom What Is an Atom Made Of? The Nucleus Protons are positively charged particles Neutrons have no electrical charge. Outside the Nucleus Electrons are the negatively charged particles in electron clouds. Chapter 4

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 3 The Atom Chapter 4 Parts of an Atom

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 3 The Atom What Is an Atom Made Of? The Nucleus positively charged particles called protons. Each proton has a mass of about 1 amu. The SI unit used to express the masses of particles in atoms is the atomic mass unit (amu). Neutrons In nucleus that have no electrical charge. Neutrons have a mass of about 1 amu Chapter 4

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 3 The Atom What Is an Atom Made Of?, continued Outside the Nucleus Electrons are negatively charged particles in atoms. Electrons are found around the nucleus within electron clouds. The charges of protons and electrons are opposite but equal, so their charges cancel out. Because an atom has no overall charge, it is neutral. Chapter 4

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 2 The Atom How Do Atoms of Different Elements Differ? Starting Simply The hydrogen atom has one proton and one electron. The helium atom has two protons, two neutrons, and two electrons. Chapter 4

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 2 The Atom How Do Atoms of Different Elements Differ?, continued Building Bigger Atoms For bigger atoms, simply add protons, neutrons, and electrons. Protons and Atomic Number atomic number = number of protons Atomic mass = number of protons + number of neutrons Chapter 4

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. Atoms Atoms are electrically neutral, so: Protons = Electrons = Atomic Number Neutrons does not have a specific relationship to protons Atomic Mass = Protons + Neutrons –Electrons have almost no mass

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. Reading the Periodic Table Name Atomic Number Symbol Avg. Atomic Mass

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. Periodic Table

13. Copyright © by Holt, Rinehart and Winston. All rights reserved. Reading the Periodic Table - Quiz How Many Protons are in –Boron (B) –Platinum (Pt) How many electrons are in: –Radium (Ra) –Magnesium (Mg) An element contains 66 electrons. What is it? An element contains 14 protons. What is it? 5 78 88 12 Dysprosium Silicon

14. Copyright © by Holt, Rinehart and Winston. All rights reserved. Calculating Protons & Neutrons ElementAtomic Mass Atomic Number ProtonsNeutronsElectrons B 24.305 8 19 11 55 5 6 Mg 12 O 168 88 K 19 201939

15. Copyright © by Holt, Rinehart and Winston. All rights reserved. Why are Atomic Masses not Even Numbers? What is the atomic mass of Carbon (C)? –12.011 What is the atomic mass of Chlorine (Cl)? –35.453 If Protons = 1 and Neutrons = 1, where does the.453 come from?

16. Copyright © by Holt, Rinehart and Winston. All rights reserved. Why not whole Numbers? Mass of both Neutron and Proton is 1.67x10 -24 Small units/hard to work with Scientists set standard based on Carbon 12 –1 atomic mass unit = 1/12 of carbon atom So Silicon is 29.974 instead of 30 –This is only part of the reason…

17. Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 2 The Atom Isotopes have the same number of protons but different numbers of neutrons. Chapter 4

18. Copyright © by Holt, Rinehart and Winston. All rights reserved. Isotopes Another thing Dalton got wrong Isotopes occur as a mixture in nature –Example Potassium: 93.25% have 20 neutrons 6.7302% have 22 neutrons 0.117% have 21 neutrons ALL have 19 Protons and 19 Electrons Isotopes have the Same Atomic Number but a Different Atomic Mass

19. Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 2 The Atom Isotopes, continued Telling Isotopes Apart by its mass number. How Many Neutrons? Calculate Neutrons = Atomic Mass – Atomic number Properties of Isotopes An unstable atom has a nucleus that will change over time. This type is radioactive. Chapter 4

20. Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 2 The Atom Isotopes, continued Chapter 4

21. Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 2 The Atom Isotopes, continued Naming Isotopes Write the name of the element followed by a hyphen and the mass number. Example: C-14 is Carbon 14 (8 neutrons) instead of 6 (C-12 is normal) Calculating the Mass of an Element The atomic mass of an element is the weighted average of the masses of the isotopes of that element. Chapter 4

22. Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 3 The Atom Math Focus Chapter 4