1. Chapter 14: Inside the Atom Pages 404 - 423

2. First Thoughts of the Atom “Cannot be divided” Keep dividing matter until only one particle remains Chemistry – study of matter

3. A Model of the Atom Element – matter made of atoms of only one kind Dalton’s Concept – –Matter is made up of atoms –Atoms cannot be divided into smaller pieces –All atoms of an element are exactly alike –Different elements are made of different kinds of atoms *Thought was like tiny marble

4. William Crookes Experiment –Showed particles were traveling in a straight line from the negative electrode to the positive –CRT – once used in TV’s and computer monitors

5. Discovering Charged Particles J.J. Thomsom – used magnet on CRT and beam was bent towards it Proved that this was not light, but made of charged particles of matter Electrons – negatively charged particles Particles smaller than atoms do exist

6. Atomic Model: –Sphere of positive charge –Negatively charged electrons spread evenly throughout positive charge –Positive=Negative –Atom is neutral –Later discovered not all atoms are neutral –More positive electrons = + atom –More negative electrons = - atom

7. Questions 1.What does the word atom mean? 2.What 4 concepts did Dalton propose about atoms? 3.What did William Crookes experiment show? 4.How did Thomson prove particles were in the CRT and not light? 5.What type of particle did Thomson discover? 6.Describe what an atom looks like. 7.How do we know if an atom is neutral or has a positive or negative charge?

8. Rutherford’s Experiments Tested Thomson’s model to see if correct Alpha particles bombarded gold foil Most passed through or veered slightly, but some bounced right back!

9. A Model with a Nucleus Hypothesized that almost all mass of an atom and all positive charge is crammed into one small space in the center called the nucleus Proton – positively charged particle in the nucleus of an atom The rest of the atom is empty space occupied by almost massless electrons

10. Neutron: –Same mass as a proton –Neutral charge –Located in nucleus –Neutral atom has equal number of protons and electrons

11. Further Developments Electrons – in constant, unpredictable motion, impossible to know precise location of an electron Electrons act as waves Electron Cloud – region surrounding nucleus where electrons travel Electron energy levels – Niels Bohr

12. Questions 1.What did Rutherford discover about the atom from his experiment? 2.What is a proton? 3.What is a neutron? 4.How does an atom get a neutral charge? 5.Describe the behavior of an electron in an atom. 6.Where are electrons located in an atom?

13. Chapter 14 Section 2: The Nucleus Pages 415 - 423

14. Identifying Numbers Atoms of different elements contain different #s of protons Atomic number is the number of protons in the nucleus of an atom of that element. Smallest: Hydrogen has 1 proton, atomic # is 1 Heaviest: Uranium has 92 protons, atomic # is 92 Elements are identified by their atomic # (doesn’t change for an element)

15. Number of Neutrons Atoms can have a varying # of neutrons in the nucleus. Isotopes are atoms of the same element that have different #s of neutrons. Mass #: the # of neutrons + protons. Strong nuclear force holds protons together that are tightly packed in the nucleus.

16. Radioactive Decay unstable nuclei have too many or too few neutrons. Radioactive decay: nucleus releases particles to become stable If protons are released the element is changed Transmutation is the changing of an element due to radioactive decay.

17. Alpha particle = 2 protons and 2 neutrons. Beta particle = high energy electron that comes from the nucleus, not from the electron cloud. Neutron becomes unstable and splits into a proton (+) and an electron (-) Electron (-) is given off Nucleus now has 1 more proton (+), and is a new element.

18. Questions 1.Define atomic number. 2.What are the smallest and heaviest elements? 3.Define Isotope. 4.What is mass number? 5.What is radioactive decay? 6.How could an element be changed during radioactive decay? 7.What is an alpha particle? 8.How does a beta particle being released affect an element?

19. Rate of Decay Half-life of a radioactive isotope is the amount of time it takes for half of a sample of the element to decay. Not affected by weather, pressure, magnetic/electric fields, or chemical reactions.

20. Carbon Dating Carbon 14 is used to find the age of once living things (fossils, dead animals, plants and humans.) Half-life of Carbon14 is 5,730 years Compare amounts of Carbon14 in old items with the amount of Carbon14 new items to determine age. Uraium 238 is used to date non living things (rocks)

21. Making Synthetic Elements Scientists create new elements by smashing atomic particles into a target element. Isotope iodine131 used to diagnose thyroid problems. Radioisotopes can help discover how pesticides move throughout an ecosystem

22. Questions 1.Define half-life. 2.What is Carbon14 used to date? 3.What is the half-life of Carbon14? 4.What is Uranium238 used to date? 5.How do scientists create new elements? 6.How are synthetic elements useful?