The Nature of Matter Textbook Inside the Atom. 1) Explain how scientists discovered particles of an atom.

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1 Models of the Atom The Nature of Matter Textbook Inside the Atom 1) Explain how scientists discovered particles of an atom. 2) Explain how today's model of the atom was developed. 3) Describe the structure of the nuclear atom. Lesson objectives Teachers' notes 1

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12 Lesson notes: Learning Target: Subject: Topic: Grade(s): Prior knowledge: The Nature of Matter Inside the Atom Scientists 6 Knowledge of atoms Students will be able to identify two models of the atom and their creators. Bell Work: Look through the periodic table. What elements to do you recognize? Make a list and identify where you find them. Lesson objectives Teachers' notes 12

13 Models of the Atom The Nature of Matter Inside the Atom John Dalton combined the idea of elements with Greek theory of the atom. Crookes invented the Cathode Ray tube examining positive and negative particles. Why are these men important to Science? Ernest Rutherford discovered the current model of the atom. J. J. Thomson discovered the electron. 13

14 John Dalton Combined Greek theory of the Atom with the idea of elements. Propose ideas about matter: 1) Matter is made up of atoms. 2) Atoms cannot be divided into smaller pieces. 3) All atoms of an element are exactly alike. 4) Different elements are made of different kinds of atoms. 14

15 John Dalton = Ideas about Matter 1. Matter is made up of atoms 2. Atoms cannot be divided smaller 3. All atoms of an element are exactly alike 4. Different elements are made of different kinds of atoms 15

16 John Dalton Dalton imagined an atom as a hard sphere that was the same throughout. 16

17 William Crookes Crookes also tested theories about atoms. He completed his experiments using a glass tube. This was know as his Cathode Ray Tube or CRT. 17

18 1870 William Crookes CRT Experiments with a glass tube; cathode ray tube. Electrodes (metal pieces) were connected to wires Anode Electrode Positive charge Negative charge 18

19 How did Crookes make the Cathode Ray Tube work? Cathode creates a negative charge. When a battery is connected with the glass tube, a green glow appeared. A shadow of the object appeared at the opposite end of the tube at the anode. Something was traveling from the cathode to the anode. The cross was getting in the way! Anode creates positive charge. Shadow which was created. 19

20 J. J. Thompson J. J. Thompson continues Crookes's discovery of a beam of light with the CRT. He placed magnets beside the beam of light, and the beam bent. Thompson concluded that the light was not really a light at all. It was charged particles. He also concluded that the particles in the tube were negatively charged called electrons. There was now evidence that particles smaller than the atom exists. Click on the links below to see examples and learn more. 20

21 Draw a model of Thomson's and Rutherford's idea of the atom. 21

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23 1897 JJ Thompson Charged Particles Light can be bent by a magnet; therefore beam is made up of charged particles Electrons Negatively charged particles 23

24 Ernst Rutherford Ernest Rutherford experimented with Thompson's findings. Rutherford wanted to see what would happen when they fired fast moving, positively charged bits of matter called alpha particles at gold (a form of metal). Rutherford thought that the particles would go straight through the gold. His experiment did not go as planned and some of the particles bounced back. He hypothesized that most charges are crammed into a small region of space at the center of the atom called the nucleus. 24

25 Today's Model With Rutherford's findings, a new model of the atom developed. Though, some of the data did not make sense. According to Rutherford's model the only other particle in the atom was a proton. That meant that the mass of the atom should have been equal to the mass of the protons. This did not add up because the mass of most atoms was at least twice as great as the mass of its protons. The scientists were puzzled. Where did the extra mass come from? It was thought that the extra mass came from another particle in the nucleus. This particle would be called a neutron, and had the same mass at the proton. The particle was neutral. 25

26 Proton 1906 Ernest Rutherford Failed experiment results in new hypothesis: the mass of the atom & its positively charged particles are located in the nucleus. Electrons Neutron Negatively charged particles have almost no mass. Extra mass accounted for as the neutron is discovered; has no charge so is neutral. 26

27 Today's Model After the neutron was discovered, Neil Bohr's calculations showed that it was impossible to know where the electrons were located in a particular time. This inspired more research. New theories of the atomic model were developed. Scientists believed that since electrons were impossible to locate, then they must be traveling in the region around the nucleus called the electron cloud. They also were more likely to be traveling closer to the nucleus since the electrons are attracted to the positive charges of the protons. 27

28 Electron Movement Niels Bohr Electrons do NOT orbit the nucleus; they are in constant unpredictable motion Electron Cloud The region around the nucleus where the electrons exist. 28

29 Let's Reveal and Review! Erase and reveal today's model of the atom with it's important parts. Protons Neutrons electrons 29

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31 Models of the Atom The Nature of Matter Textbook Inside the Atom EXIT TICKET... Go back to page 8B and answer questions 1 3 again. Is your answer different? Lesson objectives Teachers' notes 31

32 Learning Target: Students will be able to identify two models of the atom and their creators. DID WE MEET OUR LEARNING TARGET? 32

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