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Atomic Theory Part 1 History and Scientists Chemistry.

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1 Atomic Theory Part 1 History and Scientists Chemistry

2 Learning Objectives TLW research and describe the historical development of atomic theory (TEKS 6) TLW be introduced to the scientists behind the atomic theory (TEKS 3.F. & 6.A.) TLW begin to describe the relationship among electrons, protons, neutrons, atomic number, mass number, and isotopes (TEKS 6A, 6B, 11A)

3 Anticipatory Activity What’s in the Box? Lab What’s in the Box? Lab – to be done prior to beginning lecture from this PowerPoint

4 Agenda I. Atoms – Building Blocks of Matter & Subatomic Particles II. Mass of Atoms III. Meet the Scientists and Learn About Their Discoveries IV. Modern Day Atomic Theory

5 I. Atoms A. Building blocks of Matter 1. Everything is made up of atoms 2. Atom is Greek for indivisible 3. There are three major parts to the atom called subatomic particles

6 B. Subatomic Particles Most of the atom’s mass. NUCLEUSELECTRONS PROTONSNEUTRONS NEGATIVE CHARGE POSITIVE CHARGE NEUTRAL CHARGE ATOM QUARKS Atomic Number equals the # of... equal in a neutral atom Ions – lose/gain electrons Cation – positive Anion -- negative Isotope – same number of protons, different number of neutrons

7 II. The Mass of Atom A. Protons 1. are positively charge 2. have a mass of 1.67 X 10 -27 kg 3. Found in the nucleus B. Neutrons 1. Neutral 2. have a mass of 1.67 X 10 -27 kg 3. Found in the nucleus C. Electrons 1. are negatively charged 2. Have a mass of 9.11 X 10 -31 kg 3. Found orbiting outside the nucleus

8 To Put Nucleus Size in Perspective If an atom were the size of this stadium, then its nucleus would be about the size of a marble

9 Something “Quarky” About Atoms Quarks are fundamental matter particles that make up protons and neutrons 6 types – up, down, charm, strange, top, bottom Only 2 (up and down) exist in protons and neutrons, others are unstable and randomly occur We have yet to determine their mass Quarks and electrons are considered to be the smallest units of matter in the universe

10 III. The Scientists and their Discoveries

11 Democritus ATOM Smallest particle

12 Democritus (Greek philosopher) 1. Date = 400 B.C 2. Discovery = Theorized the smallest unit of an element 3. Importance = gave the term and definition of atom

13 4. Atom is Greek for “unable to divide” 5. Believed movement of atoms caused changes in matter he observed, but couldn’t prove it with evidence people would accept

14 Molecules made of atoms John Dalton Atomic Theory

15 John Dalton 1. Date = 1803 2. Discovery = a. Every element is made of atoms b. atoms of same element exactly the same c. Atoms of different elements join together to form molecules

16 Importance = proposed the ATOMIC THEORY Atomic Theory (in beginning) = 1. everything is made up of atoms 2. atoms make up molecules 3. atoms of the same element are the same 4. Atoms cannot be divided 5. in chemical reactions, atoms are combined, separated, rearranged.. …. BUT NEVER destroyed 6. aka Law of Conservation of Mass

17 Dimitri Mendeleev 1. Date = ca. 1870 2. Discovery = a. Order of elements is based on the periodic law b. Periodic Law states properties of elements will occur in a regular pattern 3. Importance = First periodic table of elements… ….arranged by mass

18 Mendeleev’s Periodic Table

19 Eugen Goldstein 1. Date = 1886 2. Discovery = a. discovered protons using cathode ray tube. Rays were observed traveling in the direction opposite of the cathode rays. b. protons are positive 3. Importance = atoms have both negative and positive particles

20 4. How? a. Using a cathode ray b. relationship between electricity and matter c. electric current was passed through various gases at low pressure in a glass tube = cathode d. In Goldstein’s Experiment: Rays were observed traveling in the direction opposite of the cathode rays. e. Later we’ll learn that In Thomson’s Experiment: Cathode Rays were attracted to positive electrical charges.

21 Discovery of the Protron In 1886, Eugen Goldstein used a cathode ray tube to discover the presence of a positively charged particle called a proton. Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.

22 William Crookes 1. Date = 1887 2. Discovery = a. discovered metals contain negatively charged particles 3. Importance = early indication of the electron

23 J.J. Thomson “Plum Pudding” model Electrons are negative

24 J.J. Thomson 1. Date = 1898 2. Discovery = a. discovered electrons b. electrons are negative 3. Importance = atoms have both negative and positive particles

25 Discovery of the Electron In 1897, J.J. Thomson used a cathode ray tube to discover the presence of a negatively charged particle called an electron. Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.

26 Max Planck 1. Date = 1899 2. Discovery = a. hot objects don’t emit energy continuously, like in a wave b. instead, energy is emitted in small, specific amounts called quanta 3. Importance = original idea of quantum theory

27 Ernest Rutherford Gold Foil Experiment Electrons outside nucleus Discovered nucleus

28 Ernest Rutherford 1. Date = 1911 2. Discovery = a. discovered nucleus b. did a “gold foil” experiment c. atoms mostly made of space 3. Importance = a. nucleus is very tiny, and positively charged b. electrons outside of nucleus

29 Rutherford’s Gold Foil Experiment  Alpha particles are helium nuclei  Particles were fired at a thin sheet of gold foil  Particle hits on the detecting screen (film) are recorded

30 Try it Yourself! In the following pictures, there is a target hidden by a cloud. To figure out the shape of the target, we shot some beams into the cloud and recorded where the beams came out. Can you figure out the shape of the target?

31 The Answers Target #1 Target #2

32 Rutherford’s Experiment As a follow up to our Introductory Activity of What’s in the Box?… We will now conduct a simple experiment to determine the size and shape of an object by indirect means…. as did Rutherford when he developed Atomic Theory –See pages 45 & 46 in Chemistry Lab Manual (Prentiss Hall) –See IPC Manual pages 122 & 123

33 Marie Skodowska Curie 1. Date = 1911 2. Discovery = a. Radioactivity of isotopes 3. Importance = paved way for use of radioactive isotopes in medical field and other applications

34 Henry Moseley 1. Date = 1913 2. Discovery = used x-ray technology to measure the number of protons in an atom 3. Importance = led to better arrangement of Periodic Table by atomic number (more on the PT later….)

35 Robert Millakan 1. Date = 1916 2. Discovery = a. measured the quantity of charge on the electron b. determined ratio of charge to mass of an electron 3. Importance = determined mass of an electron

36 Discovery Education Early Nuclear Theory

37 Niels Bohr Electrons in energy levels (orbits)

38 Niels Bohr 1. Date = 1913 2. Discovery = a. Electrons are in energy levels b. s, p, d, f orbitals c. 1 st = 2 electrons; 2 nd = 8 electrons; 3 rd = 18 electrons 4 th = 32 electrons

39 Energy Levels (more) Fixed energy levels are analogous to rungs on a ladder A person cannot stand between them, they climb from one to another to reach a greater height Similarly, an electron cannot exist between energy levels To jump from one energy level to another the electron must gain or lose energy

40 Quantums of Energy Have you heard of the term “quantum leap”? A quantum of energy is the amount of energy required to move an electron from its present energy level to the next higher one. The higher the electron is on energy ladder, the farther it is from nucleus

41 3. Importance = electrons orbit around nucleus in a certain pathway like planets around the sun. This is the Bohr Model

42 Bohr’s Model and What It Led To Discovery Streaming VIDEO

43 Wolfgang Pauli 1. Date = 1925 2. Discovery = only one electron can occupy a given quantum state 3. Importance = determined how electrons pair up and the direction of their movement

44 Erwin Schrödinger Atoms have no charge Same number of protons and electrons Quantum Mechanical Model

45 Erwin Schrödinger 1. Date = 1926 2. Discovery = electrons are impossible to find (like moving fan blades) 3. Importance = a. Developed Quantum Mechanical Model b. Atoms are neutral c. Atoms must have the same number of protons and electrons

46 Quantum Mechanical Model Mathematically based Does not define an exact path for electrons as did Bohr’s Model (orbitals) Estimates the probability of finding an electron in a certain position Sheldon from The Big Bang Theory sitcom explains Schrodinger’s Cat Model (YouTube)YouTube Another YouTube video of Schrodinger’s CatYouTube

47 Werner Heisenberg 1. Date = 1927 2. Discovery = can’t simultaneously determine position and momentum of a particle 3. Importance = predicted better known the position, less known of momentum YouTubeYouTube video on Heisenberg’s Uncertainty Principle Another YouTube video on H’s Uncertainty PrincipleYouTube

48 James Chadwick 1. Date = 1932 2. Discovery = demonstrated existence of neutron 3. Importance = this accounted for the additional mass in the nucleus of an atom

49 IV. Modern Day Atomic Theory 1. All matter is composed of atoms 2. Atoms of different elements have different properties and masses 3. Atoms can combine in chemical reactions (law of conservation of mass) 4. Atoms can be divided 5. Elements of the same atom can have different masses –Called isotopes – more later

50 Projects Atomic Timeline - For more on other contributors and exciting moments in atomic theory history click on this linklink FactBook Page for Scientist - linklink

51 IV. Section Questions 1.Which “scientist” gave us the word atom? 2. Which scientist developed the atomic theory? 3. Every element is made of atoms, atoms of the same element are exactly the same, different atoms make up molecules. These statements make up the what?

52 4. Which scientist discovered the electrons? 5. Which scientist discovered the nucleus? 6. Which scientist discovered that electrons were in energy levels? 7. Which scientist said atoms were neutral because they had equal number of protons and electrons?

53 8. What is the mass of protons? 9. What is the mass of neutrons? 10. What is the mass of electrons? 11. Which part of the atom has the least amount of mass?

54 Review Key Points Atoms are building blocks for all matter –Name the subatomic particles Name key scientists and their work in atomic theory List the 5 points of modern atomic theory

55 Independent Practice Atomic Theory Timeline Project linklink or Atomic Theorists FACTBook page linklink Word Search – write the word with its definition on the back Crossword Puzzle


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