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Atomic Theory Part 1 History and Scientists Chemistry
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)
Anticipatory Activity What’s in the Box? Lab What’s in the Box? Lab – to be done prior to beginning lecture from this PowerPoint
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
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
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
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
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
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
III. The Scientists and their Discoveries
Democritus ATOM Smallest particle
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
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
Molecules made of atoms John Dalton Atomic Theory
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
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
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
Mendeleev’s Periodic Table
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
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.
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.
William Crookes 1. Date = 1887 2. Discovery = a. discovered metals contain negatively charged particles 3. Importance = early indication of the electron
J.J. Thomson “Plum Pudding” model Electrons are negative
J.J. Thomson 1. Date = 1898 2. Discovery = a. discovered electrons b. electrons are negative 3. Importance = atoms have both negative and positive particles
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.
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
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
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
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?
The Answers Target #1 Target #2
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
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
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….)
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
Discovery Education Early Nuclear Theory
Niels Bohr Electrons in energy levels (orbits)
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
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
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
3. Importance = electrons orbit around nucleus in a certain pathway like planets around the sun. This is the Bohr Model
Bohr’s Model and What It Led To Discovery Streaming VIDEO
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
Erwin Schrödinger Atoms have no charge Same number of protons and electrons Quantum Mechanical Model
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
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
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
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
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
Projects Atomic Timeline - For more on other contributors and exciting moments in atomic theory history click on this linklink FactBook Page for Scientist - linklink
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?
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?
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?
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
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