The Structure of the Atom: Mass, Isotopes, and Radioactivity

1. Element song http://www.privatehand.com/flash/elements.html • Sheldon plays the element game http://www.youtube.com/watch?v=AmhWwSJDkaw • Sheldon sings the element song http://www.youtube.com/watch?v=qmC7b6USj40

2. Chapter 4: The Structure of the Atom

3. The parts of the atom The actual masses are 1.7 x 10-24 g for the proton and neutron and 9.1 x 10-28 g for the electron. (Thus the electron’s mass is 1/2000 that of a proton or neutron. “AMU” is a convenient way of describing relative masses.

4. The Atom • Atoms are spherically shaped. • Atoms are mostly empty space, and electrons travel around the nucleus held by an attraction to the positively charged nucleus.

5. Atomic Lingo • Atomic number (Z) = number of protons (identifies element) • (Also equal to the number of electrons in neutral atoms) • Mass number (A) = number of protons + neutrons • Neutrons = Mass # – Atomic #

6. Protons, neutrons, electrons

7. Isotopes • Atoms that have the same number of protons, but different numbers of neutrons. • This causes them to have a different mass number. • They are THE SAME ELEMENT though because they have the same number of protons.

8. Designating Isotopes • Hyphen notation—mass # written after the name of the element. Chlorine-37

9. Designating Isotopes • Nuclear Symbol—the atomic number is supposed to be placed at the bottom left of the atomic symbol and mass number at the top left • Li Mass Number 7 3 Atomic Number

10. A couple of examples 75 P Atomic # = Mass # = # protons = # electrons = # neutrons = As Atomic # = Mass # = # protons = # electrons = # neutrons = 31 33 15

11. A couple more examples 96 137 42Mo Atomic # = Mass # = # protons = # electrons = # neutrons = Ba Atomic # = Mass # = # protons = # electrons = # neutrons =

12. Ions • Ions are atoms that have a charge. • Cation – positive ion; more protons than electrons • Anion – negative ion; more electrons than protons • A cation is formed when an atom LOSES electrons. • An anion is formed when an atom GAINS electrons.

13. Protons, neutrons, electrons of Ions

14. Calculating Atomic Mass • The atomic mass of an element is the weighted average mass of the isotopes of that element. • The average atomic mass on the periodic table is determined by looking at the abundance of all the isotopes of an element.

15. Calculating atomic mass

16. Calculating Atomic Mass What is the atomic mass of the element?

17. Calculating Atomic Mass What is the atomic mass of the element?

18. Silver – 109 • Determine the atomic number, mass number, and # of protons, neutrons, and electrons.

19. Radioactivity • Nuclear reactions can change one element into another element. • In the late 1890s, scientists noticed some substances spontaneously emitted radiation, a process they called radioactivity. • A reaction that involves a change in an atom's nucleus is called a nuclear reaction.

20. Radioactive Decay • Unstable nuclei lose energy by emitting radiation in a spontaneous process called radioactive decay. • Unstable radioactive elements undergo radioactive decay thus forming stable nonradioactive elements.

21. Radioactive Decay • Alpha radiation is made up of positively charged particles called alpha particles. • Each alpha particle contains two protons and two neutrons and has a 2+ charge (a He nucleus)

22. Alpha radiation is not very penetrating—a single sheet of paper will stop an alpha particle.

23. Radioactive Decay • The figure shown below is a nuclear equation showing the radioactive decay of radium-226 to radon-222. +

24. Beta radiation is radiation that has a negative charge and emits beta particles. • Beta particles are very fast-moving electrons emitted when a neutron is converted to a proton. • Each beta particleis an electron with a 1– charge.

25. Beta particles have insignificant mass and a 1– charge. +

26. Beta radiation is a stream of fast moving particles with greater penetrating power—a thin sheet of foil will stop them.

27. Gamma raysare high-energy radiation with no mass & are neutral. • Gamma rays are highly penetrating because they have no charge and no mass. • Gamma rays almost always accompany alpha & beta radiation.

28. Radioactive Decay

30. Atoms that contain too many or too few neutrons are unstable and lose energy through radioactive decay to form a stable nucleus. • Few exist in nature—most have already decayed to stable forms.

31. Nuclear Stability • The area on the graph within which all stable nuclei are found is known as the band of stability. • All radioactive nuclei are found outside the band. • The band ends at Pb-208; all elements with atomic numbers greater than 82 are radioactive.

32. Section 4.4 A reaction that changes one element into another is called what? A.chemical reaction B.beta radiation C.nuclear reaction D.physical reaction

33. Section 4.4 Why are radioactive elements rare in nature? A.They do no occur on Earth. B.Most have already decayed to a stable form. C.They take a long time to form. D.They are too hard to detect.

34. Calculating p, n, and e in ions • A positive ion has LOST electrons. • Ex: Mg+2 has LOST 2 electrons • Ex: Al+3 has LOST 3 electrons • A negative ion has GAINED electrons. • Ex: N-3 has GAINED 3 electrons • Ex: Br- has GAINED 1 electron

35. Fill in the following chart:

36. Fill in the following chart:

37. What did these men do? • Aristotle – • Democritus – • Lavoisier – • Dalton – • Thomson – • Rutherford – • Chadwick –

38. What did these men do? • Aristotle – water, earth, fire, air • Democritus – atoms • Lavoisier – law of cons. of matter • Dalton – List of ideas about atomic theory • Thomson – electron, CRT exp, plum pudding model • Rutherford – nucleus, gold foil exp • Chadwick – neutron

39. Silver has two naturally occurring isotopes. Ag-107 has an abundance of 51.82% and a mass of 106.9amu. Ag-109 has a relative abundance of 48.18% and a mass of 108.9amu. Calculate the atomic mass of silver.

40. Calculating atomic mass

42. Picture on worksheet