Professor Lynn Cominsky Joanne del Corral Al Janulaw Michelle Curtis July 3, 2003

1. Professor Lynn CominskyJoanne del CorralAl JanulawMichelle CurtisJuly 3, 2003 The Atom’s Family NBSP Physical Science Leadership Institute

2. Standard Connections • Students know that all matter is made of small particles called atoms, too small to see with the naked eye (3) • Students know that all matter is made of atoms…(5) • Students know that each element is made of one kind of atom… (5) Prof. Lynn Cominsky

3. Some questions about the atom • What is an atom? • What are the parts of an atom? • How do we “see” the parts of the atom? • What is the structure of the atom? • Students know the structure of the atom, and know it is composed of protons, neutrons and electrons (8) Prof. Lynn Cominsky

4. Atoms – the historical view • Students know people once thought that earth, wind, fire and water were the basic elements that made up all matter (3) • The Greek Empedocle (around 492-432 BC.) divided matter into four elements, that he also called "roots": earth, air, fire and water • The word "atom" comes from the greek "a-tomos" and signifies "indivisible". This notion was invented by Leucippe of Milet in 420 BC Prof. Lynn Cominsky

5. Atoms – the historical view • In ancient times, many elements were known, including C, S, Cu, Ag, Au, Fe, Sn, Sb and Pb. The names of most of these are from the Latin words. • From 1000-1869, about 50 additional elements were discovered, many by alchemists, including As, Zn, P, Pt, Ni, N, O, Cl and Al. Prof. Lynn Cominsky

6. History (continued) • Mendeleyev’s periodic table (1869) classified and sorted elements based on common chemical properties. His table had 62 known elements, and left space for 20 elements that were not yet discovered. The elements were arranged in order of atomic number. Prof. Lynn Cominsky

7. History (continued) • The electron was discovered in 1897 by Thomson. He imagined the atom as a “raisin pudding” with electrons stuck in a cake of positive charge • In 1912, Rutherford discovered the nucleus by doing scattering experiments. He concluded the atom was mostly empty space, with a large dense body at the center, and electrons which orbited the nucleus like planets orbit the Sun Prof. Lynn Cominsky

8. History (continued) • Rutherford also realized that the nucleus must contain both neutral and positively charged particles. The neutron was then discovered in 1932 by Chadwick. Prof. Lynn Cominsky

9. First activity – Rutherford revisited • Given: a large wooden board, a mystery shape and marbles • Try to identify the shape that is hiding under the wooden board. You can only roll marbles against the hidden object and observe the deflected paths that the marbles take. Take at least five minutes to "observe" a shape. Then do a second shape. • Place a piece of paper under the board for sketching the paths of the marbles. Then analyze this information to determine the object's actual shape. Prof. Lynn Cominsky

10. Rutherford activity analysis • Black vertical line shows path of incoming marble • Red line shows path of outgoing marble • Green dotted line bisects the angle made by the incoming and outgoing lines • Reflecting surface is perpendicular to bisecting line Prof. Lynn Cominsky

11. Questions about Rutherford activity • Draw a small picture of each shape you studied in your lab notebook. • Can you tell the size of the object as well as its shape? • How could you find out whether the shape has features that are small compared to the size of your marbles? • Without looking, how can you be sure of your conclusions? Prof. Lynn Cominsky

12. What Rutherford really did • Rutherford shot alpha-particles (Helium nuclei) at a thin gold foil. He found that most went right through. However, some were deflected, and a percentage of those bounced right back at him! He said that “it was like firing a cannonball at tissue paper, and having it ricochet off!” • Can you see how he concluded that the nucleus was a hard small sphere, and that most of the atom was empty space? (As opposed to a plum pudding?) Prof. Lynn Cominsky

13. Vocabulary • Electron: negatively charged fundamental particle • Proton: positively charged fundamental particle • Neutron: uncharged fundamental particle • Nucleus: small, central unit in the atom that contains neutrons and protons • Atom: smallest unit of an element Prof. Lynn Cominsky

14. ELD Activities: Analogies, Imagery and Student Involvement • Rutherford simplified -- Have a small group of students (5-6) represent an atomic nucleus, by standing in a circle facing outward. • Have the rest of the students stand around at random spots, to represent the alpha particles. • Assign these students a straight path - either toward the circle or missing it. • If they bump into the circle, they should turn around and the children in the circle gently push them back to where they came from. • Some will bounce back and some will keep going. Prof. Lynn Cominsky

15. Publisher’s Materials • Take some time to look through the state-adopted texts to find activities relating to atoms that could be used in your classroom. Prof. Lynn Cominsky

16. Break – some things to think about • We all know that “opposites attract” and “like charges repel” –SO: • If electrons are negatively charged and protons are positively charged, why don’t the electrons fall into the nucleus? ? Prof. Lynn Cominsky

17. Standard connections • Science experiments show that there are more than 100 different types of atoms, which are presented in the periodic table of the elements (3) • Students know that the elements are organized in the periodic table by their chemical properties (5) • Students know how to use the periodic table to identify elements in simple compounds (8) Prof. Lynn Cominsky

18. Some questions: • What is an element? • Why are nuclei and atoms stable? • What is a molecule? http://www.caffeinearchive.com/images/molecule.gif Prof. Lynn Cominsky

19. Key Concepts and Vocabulary: Atoms, Elements and Molecules • Atom: smallest unit of an element • Element: any of more than 100 fundamental substances that consist of atoms of only one kind • Molecule: a collection of atoms, bound together. • Molecules can be made from only one element, such as H2 or O2 • Molecules can be made from different elements, such as H2O or CO2 Prof. Lynn Cominsky

20. p n e Parts of an Atom • Each element in the Periodic Table has a different number of protons in its nucleus • Protons have positive charge • Change the number of protons  change elements • This is called nuclear physics • The element also has the same number of electrons • Electrons have negative charge • Change the number of electrons  ionize the element • This is called chemistry • Some elements also have neutrons • Neutrons have no charge • They are in the nuclei of atoms Prof. Lynn Cominsky

21. p e The Hydrogen Atom • One electron orbiting a nucleus • 1 proton = Z = atomic number • 0 neutrons = N • Total mass = A = Z+N =1 • Singly ionized Hydrogen is missing one electron = 1H+ • Add a neutron and you have Deuterium = 2H = D 1H Prof. Lynn Cominsky

22. p p n n e e The Helium Atom • Two electrons orbiting a nucleus • 2 protons = Z = atomic number • 2 neutrons = N • Total mass = A = Z+N =4 • Singly ionized Helium is missing one electron =4He+ • Doubly ionized Helium is missing both electrons =aparticle =4He++ 4He Prof. Lynn Cominsky

23. p n n p p n e e e Isotopes and Elements • If Helium loses one of its protons (and one of its electrons), it becomes a different element • If Helium loses one of its neutrons, it becomes an isotope 3H (Tritium) 3He Prof. Lynn Cominsky

24. History of the atom (Part 2) • Following Rutherford’s planetary model of the atom, it was realized that the attraction between the electrons and the protons should make the atom unstable • Bohr proposed a model in which the electrons would stably occupy fixed orbits, as long as these orbits had special quantized locations Prof. Lynn Cominsky

25. History of the atom (continued) • In the Bohr model, the electron can change orbits, accompanied by the absorption or emission of a photon of a specific color of light. Prof. Lynn Cominsky

26. History of the atom (continued) • Modern quantum theories lead to stable locations of electrons, which are not exact planetary orbits, but are characterized by specific quantum numbers. • Each electron shell is characterized by a different principle quantum number, usually called n. Prof. Lynn Cominsky

27. History of the atom (continued) • In quantum theory, the electron shells are not fixed orbits, but clouds of probability. You can’t measure the exact location of the electron. • Each electron orbital has a different shape, and no two electrons can be in the same orbital (unless they have opposite spins.) Prof. Lynn Cominsky

28. History of the atom (continued) • The quantum rules for the electron orbitals in an atom determine the row structure in the periodic table. • The geometry of the electron orbitals determines the structure of an atom Prof. Lynn Cominsky

29. History of the atom (continued): • The spin of the electron is another quantum property. In the planetary model, it is similar to the spin of the Earth on its axis. There are two choices for the orientation of the electron’s spin axis: up or down. Some further questions: • What is periodic about the periodic table? • What types of chemical properties are used to classify the elements? Prof. Lynn Cominsky

30. ELD Activity: Visual Imagery and Identifying elements • Make a list of all the element names that you know (e.g., Carbon, Oxygen, Silicon) • What are some of the common household items that contain these elements? • Draw a picture of the items Element Item Drawing Prof. Lynn Cominsky

31. Lunch puzzler • How do nuclei stay together when they are filled with positive charges? ? Prof. Lynn Cominsky

32. Periodic Table of the Elements Review: What are the numbers in each box? Prof. Lynn Cominsky

33. Navigating the Periodic Table • The rows are the “periods” • Each period starts a new shell of electrons • The periods are numbered starting with 1 at the top • The columns are the “groups” • Each group has similar chemical properties • The groups are numbered starting with 1 at the left • Elements with similar properties have the same number of electrons in the outermost shell Prof. Lynn Cominsky

34. Electron shells and atomic structure • The first shell will hold up to two electrons. The orbital is spherical, and called 1s. The first row of the periodic table consists of 2 elements with 1s electrons. • The second (and third) rows each add eight electrons. The shells that are filled are made of a spherical orbital that holds 2 electrons, called 2s or 3s, and 3 non-spherical orbitals that hold a total 6 electrons, called 2p or 3p. Prof. Lynn Cominsky

35. Electron shells and atomic structure • In the fourth row of the periodic table, the 4s orbital fills first, then a new orbital, 3d, begins to be filled. It can hold 10 electrons. p-orbitals Prof. Lynn Cominsky

36. Electron shells and atomic structure • What orbital is being filled in row 4 after 3d is filled? • What is the pattern that repeats in row 5? d-orbitals Prof. Lynn Cominsky

37. Electron shells and atomic structure • In row 6, a new type of orbital, 4f, appears in between elements 57 and 72. All the elements with 4f electrons have very similar chemical properties. They are known as the Lanthanides (after element Z=57, Lanthanum) or rare earths. • A similar pattern repeats in row 7, with the 5f orbitals filling between elements 89 and 104. These elements also have similar chemical properties, and are called the Actinide elements (after element Z=89, Actinium). • There are 7 different f-orbitals: each can hold 2 electrons for a total of 14 in the 4f or 5f orbitals. Prof. Lynn Cominsky

38. p p p e e e Third activity: Shell structure • Carbon=C • Sodium=Na • Neon=Ne • Chlorine=Cl How many protons and electrons do these elements have? Draw the electron shell structure for each. Review: what is this element? Prof. Lynn Cominsky

39. Shell structure: thinking deeper • Where are the elements with very stable outer shells in the periodic table? What do we call them? • Where are the elements with one electron outside a filled shell? • Where are the elements that need one electron to fill their shells? • What happens when these two types of elements are combined chemically? • So, what are some rules for making molecules? Prof. Lynn Cominsky

40. Key concepts: Periodic Table • The number of elements in each of the horizontal rows (periods) in the periodic table, are due to the quantum rules that govern the electron orbitals. • In vertical columns (groups) in the periodic table, similar chemical properties are due to the number of electrons in filled or unfilled shells. • Completely filled shells make an atom very stable • Elements with 1 or 2 electrons outside of filled shells or with 1 or 2 missing electrons are very chemically reactive. They always try to combine with other elements that can fill their shells. Prof. Lynn Cominsky

41. Vocabulary • Atomic number: the number of protons in the nucleus of an element • Atomic mass: the total mass in one atom of an element • Ionization: removal of electrons from an atom • Quantum: a very small discrete unit of light or energy Prof. Lynn Cominsky

42. ELD Activities:Academic Language • What is meant by the phrase quantum leap? • Is this phrase consistent with the scientific definition of the word quantum? ELD Activities:Visual Imagery • Use modeling clay to represent atomic structure. Use different colors for protons, neutrons and electrons. Have the students try different combinations for different elements Prof. Lynn Cominsky

43. Publisher’s Materials • Take some time to look through the state-adopted texts to find activities relating to the periodic table that could be used in your classroom. • Examples: HC p. C46 Prof. Lynn Cominsky

44. F = k q1 q2 r2 Thinking deeper: The forces in the atom • Electrons are bound to nucleus by the Coulomb (electromagnetic) force • Protons in nucleus are held together by the strong nuclear force • Neutrons can decay into protons by weak nuclear force, emitting an electron and an anti-neutrino. The weak force is also responsible for radioactivity. n = p + e+n Prof. Lynn Cominsky

45. Thinking deeper: The forces in the atom • There are four fundamental forces in physics. • Gravity and the electromagnetic forces both have infinite range but gravity is 1036 times weaker at a given distance • The strong and weak forces are both short range forces (<10-14 m) • The weak force is 10-8 times weaker than the strong force within the nucleus Prof. Lynn Cominsky

46. Standard connections • Students know metals have properties in common, such as high electrical conductivity (5) • The organization of the periodic table is based on the properties of the elements and reflects the structure of atoms. Students know how to identify regions corresponding to metals, nonmetals and inert gases (8) Prof. Lynn Cominsky

47. Fourth Activity: Electrical conduction • How can we tell which elements are good electrical conductors? • Are all metals good conductors? • Are all good conductors metals? • How can we tell which materials are good electrical insulators? • How do you think the electrons in conductors differ from those in insulators? Prof. Lynn Cominsky

48. Equipment for Electrical Conduction activity • Insulated wires • Batteries • Bulbs • Other things like rubber, wood, glass, plastic, aluminum, paper clips, etc. • Masking tape Prof. Lynn Cominsky

49. More questions for Electrical Conduction activity • Were you surprised by the some of the items that were conductors? • Were you surprised by some of the items that were insulators? • What did the conductors have in common? • What did the insulators have in common? Prof. Lynn Cominsky

50. Electrical Conductors: A deeper look • The best conductors are Copper (Cu), Silver (Ag) and Gold (Au) • Cu has Z=29, Ag has Z=47 and Au has Z=79 • How are these electrons arranged? 29 = 2+8+8+10+1 47 = 2+8+8+18+10+1 79 = 2+8+8+18 + 18+14+10 +1 • So, why are these elements good conductors? Prof. Lynn Cominsky