Chapter 11- Introduction to Atoms

1. 8th Grade Science Chapter 11- Introduction to Atoms

2. Alabama Course of Study • #2 Describe the structure of atoms, including the location of protons, neutrons, and electrons. • Identifying the charge of each subatomic particle • Identifying Democritus and Dalton as contributors to the atomic theory

3. Chapter 2- Introduction to Atoms Section 1: Development of the Atomic Theory Section 2: The Atom

4. Outcomes • Students will: • Describe some of the experiments that led to the current atomic theory. • Compare the different models of the atom. • Explain how the atomic theory has changed as scientists have discovered new information about the atom.

5. Development of the Atomic Theory What Do You Think? Imagine that you have cut a penny in half. Then, you take one piece and half it again. Will this continue forever, or will you come to a point where no more cutting is possible?

6. Remember, matter what everything is made of. • The smallest part of matter are called atoms. • All matter is made of atoms. • It started with a man, a knife, and an apple.

7. Development of the Atomic Theory • Democritus was a Greek philosopher who theorized that all matter was made of invisible particles called atoms. • The word atom means uncuttable or indivisible. Democritus of Abdera, about 460-370 BCE

8. Development of the Atomic Theory • His views contrasted those of Aristotle, who believed in the four elements; earth, water, air, fire.

9. Development of the Atomic Theory • Most of our knowledge of Democritus comes from negative remarks about him in others’ writings.

10. Development of the Atomic Theory • Dalton, a British chemist and teacher, did studies and experiments in weather, colorblindness, and gases. John Dalton 1766-1844

11. Development of the Atomic Theory He noticed that elements, a substance that cannot be separated or broken down into simpler substances by chemical means, combine in specific proportions to form compounds, a substance made up of atoms of two or more different elements joined by chemical bonds,, and theorized that their atoms combine at the same proportions

12. Development of the Atomic Theory Thomson’s experiments using a cathode-ray tube showed that smaller particles make up atoms Joseph John “J.J.” Thomson 1856-1940

13. Development of the Atomic Theory Thomson received the Nobel Prize in physics in 1906 for his discovery of the electron.

14. Plum-pudding Model • Thomson proposed that electrons were located throughout an atom like plums in a pudding, as shown in this model. • Today, you might call Thomson’s model the chocolate chip ice-cream model.

15. Bell Ringer • Prediction: • What do you think was wrong with the plum- pudding model? Explain.

16. VIDEO • Jot Notes as you watch the video • Duell Chemistry • Gold Foil Experiment

17. Development of the Atomic Theory • Rutherford, a former student of Thomson’s from New Zealand, tested his teacher’s theories in his Gold Foil Experiment. • He expected his alpha particles to go straight through the foil, and most of them did. Ernest Rutherford 1871- 1937

18. Development of the Atomic Theory • But some of the particles were deflected or bounced straight back! • This showed that a nucleus with a positive charge makes up the center of an atom. Rutherford’s Gold Foil Experiment

19. Rutherford’s Model of the Atom • Rutherford’s model of the atom had electrons surrounding the nucleus at a distance. • He calculated that the diameter of the nucleus was 100,000 times smaller than the diameter of the gold atom. Similar to a stick pin on a football field.

20. Development of the Atomic Theory Bohr, a Danish scientist who worked with Rutherford, described the motion of electrons around the nucleus. Niels Bohr 1885-1962

21. Development of the Atomic Theory Bohr said that electrons orbit the nucleus at specific energy levels, and can move from one level to another. Bohr’s Atomic Model

22. Development of the Atomic Theory To do this, Bohr said, the electrons must absorb or release energy, often in the form of light.

23. Development of the Atomic Theory Erwin Schrödinger and Werner Heisenberg’s work with the uncertainty principle explained that electrons do not travel in orbits. In fact, the exact path of a moving electron cannot be predicted. Schrödinger & Heisenberg

24. Development of the Atomic Theory The current atomic theory states that there are regions inside an atom where electrons are likely to be found. These regions are called electron clouds. Electron Cloud Model

25. Summary • Democritus thought that matter is composed of atoms. • Dalton based his theory on observations of how elements combine. • Thomson discovered electrons in atoms. • Rutherford discovered that atoms are mostly empty space with a dense, positive nucleus. • Bohr proposed that electrons are located in levels at certain distances from the nucleus. • The electron-cloud model represents the current atomic theory.

26. Quiz • What error did Thomson find in Dalton’s atomic theory? • What is the name for Thomson’s model of the atom • What is the current model of the atom called?

27. Quiz • What error did Thomson find in Dalton’s atomic theory? • What is the name for Thomson’s model of the atom • What is the current model of the atom called? • Thomson discovered that atoms are made of smaller parts. • The plum-pudding model • The electron-cloud model

28. Homework Create this table.

29. Bell Ringer What Do You Think? Which scientist do you think made the most important discovery in regards to the atom? Explain.

30. Turn and Talk Share your table with your neighbor.

31. Today you are going to create a book showing how the atomic theory has changed over time. • Materials: • Copy Paper (7 pieces per group) • 1 of the pages is a title page • Colored Pencils/Markers/Crayons • Pens or Pencils • Stapler (to bind the book) • Yesterday’s Notes

32. Steps: • 1. You will work in the groups that I assign you. • 2. You will receive two grades for today’s assignment. • 1 for participation • 1 for the following criteria • 2. You MUST include the following in your book: • Pictures of the different atomic models • The names of the scientists that we discussed • What they discovered • The dates that the discovery happened • If time permits, you may also want to include: • Drawings of the experiments • Drawings of the people • 3. Be Creative and colorful! • 4. Staple the left side of all the pages together in the correct order.

33. The Atom What Do You Think? What is the smallest thing you have ever seen? How does it compare to the size of an atom?

34. How Small is an Atom? • Think about a penny. • It contains about 2 X 10²² atoms. • (20,000,000,000,000,000,000,000 atoms) • That’s 20 thousand billion billion atoms • In other words, atoms are really small!

35. Scientists know that aluminum is made of average-sized atoms. • An aluminum atom has a diameter of about 0.00000003 cm. That’s three one-hundred-millionths of a centimeter. • Aluminum foil is about 50,000 atoms thick!

36. Parts of the Atom The atom is made up of even smaller parts. Protons Neutrons Electrons Because the masses of particles in atoms are so small, scientists made a new unit for them. The SI unit used to express the masses of particles in atoms is the atomic mass unit. (amu) Nucleus

37. Parts of the Atom The nucleus is the small, dense, positively charged center of the atom. It contains most of its mass. Protons are positively charged particles in the nucleus of the atom. Neutrons are particles in the nucleus that have no charge Nucleus

38. A neutron walks into a diner and orders a glass of orange juice at the lunch counter. When the waiter brings the juice, the neutron asks, “How much do I owe you?” • The waiter replies, “For you, no charge.”

39. Parts of the Atom Nucleus The electrons are negatively charged particles found in the electron clouds out side the nucleus. The size of the electron cloud determine the size of the atom.

40. Parts of the Atom The current atomic theory states that there are regions inside an atom where electrons are likely to be found. These regions are called electron clouds. Electron Cloud Model

41. Parts of the Atom The compared to protons and neutrons, electrons are very small in mass. It takes more than 1,800 electrons to equal the mass of 1 proton. The mass of an electron is so small that it is usually thought of as almost zero. Electron Cloud Model

42. Charges • 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. • What happens if the numbers of electrons and protons are not equal? • The atom becomes a charged particle called an ion. • An atom that loses and electron becomes a positively-charged ion. • An atom that gains one or more extra electrons become a negatively-charged ion.

43. The following image shows Na losing an electron and Cl gaining an electron • Thus the Na becomes Na+ • The Cl becomes Cl-

44. VIDEO • Atoms vs. Ions

45. How does an atom become a positively-charged ion?

46. How does an atom become a positively-charged ion? • An atom becomes a positively-charged ion when it loses an electron.

47. Create a Visual • Create a visual representation of the element Aluminum changing from an Aluminum atom to an Aluminum ion.

48. The Atom What Do You Think? What are some differences you use to tell one of your classmates from another?

49. Brainstorm • Brainstorm: • How do you think you calculate the atomic number? • Write down your ideas.

50. How do Atoms of Different Elements Differ? • There are more than 110 different elements. • The atoms of each of these elements are different from the atoms of all other elements. • Imagine that you could build an atom by putting together protons, neutrons, and electrons.