1. Chapter 6 Introduction to Atoms

2. Ch 6 Sec 1 Development of Atomic Theory

3. Vocabulary Atom Electron Nucleus Electron cloud

4. Vocabulary Atom – Smallest unit of an element that still maintains the properties of that element Electron – Subatomic particle – Negative charge

5. Vocabulary Nucleus – Atom’s central region – has protons and neutrons Electron Cloud – Region around the nucleus where electrons are found

6. Beginning of Atomic Theory Democritus – Greek philosopher 440 BCE – Thought you cut any thing till at some point you could cut it down into anything simplier Atomos – Not able to be divided

7. Dalton’s Atomic Theory By 1700s science was in full swing John Dalton – Wanted to know why compounds always form in set ratios – Set forth 3 key theories All substances made of atoms. Atoms cannot be created or destroyed Atoms of same elements are identical Atoms join with other atoms to make new substances

8. Thomson’s Discovery of Electrons In 1837 JJ Thomson discovered the electron – Proved that the atom isn’t the smallest particle Found negatively charged particle – Electron Thought electrons scattered throughout the atom – Plum pudding model

9. Rutherford’s Atomic “Shooting Gallery” In 1909 Ernest Rutherford wanted to tested Thomson’s subatomic particle idea Aimed positive particles at a thin sheet of gold foil – Most positive particles passed through but some bounced off to side and some bounced back

10. Nucleus and the Electrons Rutherford’s experiment proved that there’s a nucleus – Dense center of the atom – Positive charge

11. Copy these diagrams

12. Nucleus & Electrons Bohr’s electrons levels – Electron’s move in definite energy levels outside the nucleus. – Electrons only in those energy levels, never in between

13. Nucleus & Electrons Modern Atomic Theory – Electrons still in energy levels – But can move from level to level

14. Ch 6 Sec 2: The Atom

15. Vocabulary Proton Atomic mass unit Neutron Atomic number Isotope Mass number Atomic mass

16. Vocabulary Define on your own!

17. Parts of the Atom There are 3 main subatomic particles – Proton Positive charge – Neutron No charge, neutral – Electron Negative charge

18. Parts of an Atom The number of subatomic particles determine how the atoms behaves – Change the # of protons = change the element – Change the # of neutrons = change the weight of the atom – Change the # of electrons = change how the atom may form chemical bonds

19. Parts of an Atom Only protons and neutrons have measurable mass Mass measured in “amu” units – Atomic mass unit

20. Parts of an Atom Electrons – Compared to protons & neutrons, electrons have extremely small mass – Negative charge of one electron cancels the positive charge of one proton – Ion An atom with unequal # of electrons vs protons Very important to chemical bonding!

21. Atoms and Elements Role of Neutrons – Act as a buffer to the positive charges of the protons Otherwise the nucleus would tear apart – Nucleus does not have to equal number of neutrons and protons Generally more neutrons than protons inside an atom’s nucleus

22. Atoms and Elements Atomic number of an element = number of protons – Every oxygen atom has 8 protons – If you change the number of protons, you change the element!

23. TEST ALERT….. # of protons = Atomic Number

24. Isotopes Can vary the number of neutrons Isotopes – Atoms of the same elements, but with different number of protons

25. Isotopes Radioactive atoms – Have unstable nucleus and decay at fast rates Nearly all isotopes of the same elements have similar chemical and physical properties

26. Isotopes Difference in isotopes – Mass number = sum of protons and neutrons MN = P + N – Carbon isotope 6 protons 10 neutrons mass number = 6 + 10 = 16

27. Isotopes Naming Isotopes – Write the name of the element, followed by a hyphen and the mass number oxygen-18 Mass = protons + neutrons 18 = 8 protons + ____ neutrons 18 = 8 protons + 10 neutrons

28. Isotopes Atomic mass – Weighted average of all the isotope mass numbers naturally occurring – Most elements found in nature contain a mix of 2 or more isotopes

29. Forces in Atoms Gravitational force – Pulls particles together Electromagnetic Force – Particles with same charge repeal each other – Reason for neutrons in a nucleus

30. Forces in Atoms Strong Force – Helps to keep protons near each other Weak Force – In radioactive isotopes Plays role when neutrons change to protons or electrons – Changing is nuclear reaction