Nature of Science

1. Nature of Science • Bell Ringer: How do you know something exists if you have never seen it before? Important Vocabulary • Inference • Indirect evidence

7. The Black Box Lab • Purpose • Materials • Procedure • Results Table (20 pts) • Post Lab Questions (30 pts)

10. Results (20 pts)

11. Post Lab Questions (30pts) • How did you construct your model of what was in the boxes? • How do you know if something exists if you have never seen it before? • How does this lab relate to the scientific method? • To create a more accurate model, what would you want to do next without looking inside the boxes? • How do you think scientists use or have used empirical evidence to create models? (hint: think about topics in this class)

12. Contents of Each Box • Box 1- Wooden block • Box 2 - 3 Pennies • Box 3 - 2 Straws • Box 4 - 10 Stickers • Box 5 - Pill Canister • Box 6 – 2 Rubber bands • Box 7 - 1 Dice • Box 8- 10 Beads • Box 9 - 10 Lima Beans • Box 10 - 2 Cotton Balls

13. What does an atom actually look like? Closure: watch video “have you ever seen an atom?” Exit Pass – how does today’s lab relate to the discovery of the atom?

14. Historical Scientists Jigsaw Activity • It is now your turn to do some research… • You will be assigned a scientist to become an expert on • This scientist had an impact on the historical development of the atom • YOUR JOB: give a creative, informative poster on your scientist and how they influenced the historical development of the atom • You are then going to share your poster with others to inform them about your scientist.

15. Textbook Info • Dalton – pg 77-78 • Thomson – pg 79 • Rutherford – pg 81 • Bohr – pg 91 • DeBroglie – pg 91

16. Atoms New section in table of contents

17. Aristotle & Democritus • First philosophers to start thinking about the atom and its component • Smallest divisible component vs. indivisible particle

18. Dalton • Billiard Ball Model • Provided evidence for how we know atoms exist

19. EQ 1: How do we know atoms exist? • KC 1: Law of definite proportions – a chemical compound always contains the same elements in exactly the same proportions by weight or mass • KC 2: Law of conservation of mass • KC 3: Law of multiple proportions – when 2 elements combine to form 2 or more compounds, the mass of one element that combines with a given mass of the other is in the ratio of small whole numbers

20. EQ 2: What are the five postulates of Dalton’s atomic theory • The ancient Greeks tried to explain matter, but the scientific study of the atom began with John Dalton in the early 1800's.

21. EQ 2: What are the five postulates of Dalton’s atomic theory • KC 1: All matter is composed of extremely small particles called atoms, which cannot be subdivided, created, or destroyed • Many ancient scholars believed matter was composed of such things as earth, water, air, and fire. • Many believed matter could be endlessly divided into smaller and smaller pieces

22. EQ 2: What are the five postulates of Dalton’s atomic theory • KC 2: Atoms of a given element are identical in their physical and chemical properties • KC 3: Atoms of different elements differ in their physical and chemical properties

23. EQ 2: What are the five postulates of Dalton’s atomic theory • KC 4: Atoms of different elements combine in simple, whole-number ratios to form compounds • KC 5: In chemical reactions, atoms are combined, separated, or rearranged but never created, destroyed, or changed

24. Thomson • Plum pudding model • Introduced the idea that electrons are located outside the nucleus

25. Rutherford • Discovered the nucleus • Used the gold foil experiment

26. EQ 3: What model of the atom will we use? • KC 1: Bohr suggested that electrons move in circular orbitals around the nucleus • Bohr’s model of the atom gives us a good starting point for understanding more about the atom

27. EQ 3: What model of the atom will we use? KC 2: How to draw a Bohr model of an atom • Find your element on the periodic table. • Determine the number of electrons – it is the same as the atomic number. • Determine the number of circular orbits the atom has. • Add electrons = atomic number - 1st shell can hold two - 2nd and 3rd can hold eight

28. Bohr model of the atom Elements in the 1st period have one energy level. Elements in the 2nd period have two energy levels, and so on.

29. Bohr model of the atom C Draw a nucleus with the element symbol inside. Carbon is in the 2nd period, so it has two energy levels, or shells. Draw the shells around the nucleus.

30. Bohr model of the atom Element name Atomic number = number of protons = number of electrons (for now…) Element symbol Average atomic mass

31. Bohr model of the atom • Add the electrons. • Carbon has 6 electrons. • The first shell can only hold 2 electrons. C

32. Bohr model of the atom • Since you have 2 electrons already drawn, you need to add 4 more. • These go in the 2nd shell. • Add one at a time -starting on the right side and going counter clock-wise. C

33. Bohr model of the atom • Check your work. • You should have 6 total electrons for Carbon. • Only two electrons can fit in the 1st shell. • The 2nd shell can hold up to 8 electrons. • The 3rd shell can hold 18, but the elements in the first few periods only use 8 electrons. C

34. Bohr model of the atom • KC 3: The lowest allowable energy state of an atom is called its ground state. • KC 4: When an atom gains energy, it is in an excited state. • Wavelike properties of electron help relate atomic emission spectra, energy states of atoms, and atomic orbitals

36. Bohr model of the atom • A photon is a particle of electromagnetic radiation having zero mass and carrying a quantum of energy. • When a photon strikes an atom it gives the atoms more energy. If enough photons strike an atom it may cause electrons to jump levels.

37. Bohr model of the atom KC 5: The excited state occurs when an atom has a higher potential energy than it has at its ground state. When an excited atom falls back to its ground state the substance will give off a unique color of light.

38. Bohr model of the atom • KC 6: The behavior of electrons is still not fully understood, but it is known that they do not move around the nucleus in circular orbits • We use Bohr’s model because it is easy to picture and gives us a basic understanding of the atom

39. Whiteboard Practice • Draw the Bohr model for the following elements: • Boron • Calcium • Chlorine • Nitrogen

40. EQ 4: What is an atom made of?

41. EQ 4: What is an atom made of? • KC 1: An atom is made of a nucleus containing protons and neutrons. Electrons move around the nucleus.

42. EQ 4: What is an atom made of? • KC 2: The number of protons and the mass number define the identity of the atom • Each element contains a unique positive charge in their nucleus

43. What is an atom made of? • KC 3: The number of protons in the nucleus of an atom identifies the element and is known as the element’s atomic number

44. Atoms and Isotopes • All atoms of a particular element have the same number of protons and electrons but the number of neutrons in the nucleus can differ • KC 4: Atoms with the same number of protons but different numbers of neutrons are called isotopes

47. Atomic Mass and Isotopes • The relative abundance of each isotopes is usually constant • Isotopes containing more neutrons have a greater mass • Isotopes have the same chemical behavior • KC 5: The atomic mass is the sum of the protons and neutrons in the nucleus

48. Atomic Mass and Isotopes

49. Isotopes • There are 2 ways you will see isotopes written: Aluminum-27Al 27 13

50. Atomic Mass • One atomic mass unit (amu) is defined as 1/12th the mass of a carbon-12 atom • One amu is nearly, but not exactly, equal to one proton and one neutron.