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ch 4 notes sept 30 oct 1.notebook CHAPTER FOUR: THE STRUCTURE OF THE ATOM Sep 244:05 PM Section 4.1 Early Ideas About Matter • Compare and contrast the atomic models of Democritus, Aristotle, and Dalton. • Understand how Dalton's theory explains the conservation of mass. October 01, 2013 The Structure of the Atom Section 4.1 Section 4.2 Section 4.3 Section 4.4 Early Ideas About Matter Defining the Atom How Atoms Differ Unstable Nuclei and Radioactive Decay Sep 2711:26 AM The Atom Smallest particle of an element that retains the properties of that element * made of much smaller particles * our concept is a result of generations of work theory: an explanation supported by many experiments; is still subject to new experimental data, can be modified, and is considered successful if it can be used to make predictions that are true 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. Sep 2711:27 AM Early atomic theory begins with... Democritus * 400 BC * Claimed the world was nothing but empty space and atoms "All matter is made of very small particles much too small to see." Sep 2411:24 AM Aristotle *criticized Democritus* (384322 BC) *thought the world was made of "hyle" (continuous matter) *Did NOT believe in atoms *Thought all matter was continuous atomos: indivisible * different types of atoms = different sizes, shapes and movement = different types of properties * believed that atoms could not be created, destroyed or further divided. Sep 147:27 AM * He couldn't wrap his mind around the concept of empty space! Sep 2410:40 AM 1 ch 4 notes sept 30 oct 1.notebook If these spheres represent atoms and molecules in the gas phase, what is between them? October 01, 2013 Aristotle believed that matter is made of... Sep 3010:35 AM But really, what did it matter what philosophers thought when they had no experimental data to support their ideas? Sep 244:11 PM • Democritus (460–370 B.C.) was the first person to propose the idea that matter was not infinitely divisible, but made up of individual particles called atomos. • Aristotle (484–322 B.C.) disagreed with Democritus because he did not believe empty space could exist. • Aristotle’s views went unchallenged for 2,000 years until science developed methods to test the validity of his ideas. Sep 244:13 PM Sep 2711:30 AM Law of Conservation of Mass Mass is neither created nor destroyed during ordinary chemical reactions or physical changes 2H2O 100.00g Improved balances helped scientists accurately measure masses of elements and compounds. This lead to several laws: 1. Law of Conservation of Mass 2. Law of Definite Proportions 3. Law of Multiple Proportions Sep 2410:46 AM 2H2 + O2 11.21g H H Antoinne LaVoisier H H 88.79g O O O H H H H O Sep 2410:49 AM 2 ch 4 notes sept 30 oct 1.notebook Law of Definite Proportions October 01, 2013 Not to be confused with THE LAW OF MULTIPLE PROPORTIONS Proust 2 or more different compounds can be composed of the same elements A chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound H2O2 vs H2 O water vs. hydrogen peroxide H 2O CO vs CO2 carbon monoxide vs. carbon dioxide 2:1 Sep 148:24 AM Sep 168:09 AM John Dalton * 1800's * Studied experiments of others * Came up with a feasible theory about atoms Sep 2410:37 AM Sep 309:15 AM Section 4.2 Defining the Atom Section 4.1 Assessment Who was the first person to propose the idea that matter was not infinitely divisible? A. Aristotle B. Plato C. Dalton D. Democritus Dalton’s theory also conveniently explained what? A. the electron B. the nucleus C. law of conservation of mass D. law of Democritus • Define atom. • Distinguish between the subatomic particles in terms of relative charge and mass. • Describe the structure of the atom, including the locations of the subatomic particles. model: a visual, verbal, and/or mathematical explanation of data collected from many experiments atom cathode ray electron nucleus proton neutron An atom is made of a nucleus containing protons and neutrons; electrons move around the nucleus. Sep 2711:31 AM Sep 2711:34 AM 3 ch 4 notes sept 30 oct 1.notebook October 01, 2013 The Atom: smallest particle of an element that retains the properties of the element. The Atom Xe on nickel CO molecules on Pt Made with atomic force microscope • An instrument called the scanning tunneling microscope (STM) allows individual atoms to be seen. Sep 244:42 PM Sep 148:36 AM Scanning Tunneling Microscope Iron on copper Nanotechnology Sep 244:48 PM How was the electron discovered? * study of electricity and matter Crooke's Tube Sep 3010:32 AM Thomson found the charge/mass ratio of an electron * JJ Thomson (1897) * cathode ray tube: tubes with nearly a vacuum inside Cathode rays = electrons * determined the mass to be much tinier than a H atom * Dalton was wrong! * Nobel Prize for Thomson in 1906! Woot! Cathode rays were deflected by a magnet just like an electric current () Cathode rays moved a small paddle wheel (had mass) The mass of the particle was much smaller than that of a hydrogen atom. Sep 148:15 AM Sep 245:00 PM 4 ch 4 notes sept 30 oct 1.notebook Robert A Millikan What he discovered: October 01, 2013 The Electron (cont.) • Matter is neutral. * mass of the electron is about 1/1837 the mass of the simplest hydrogen atom * confirmed the electron carries a negative electric charge • J.J. Thomson's plum pudding model of the atom states that the atom is a uniform, positively changed sphere containing electrons. * all elements produce identical cathode rays * proved atoms are divisible What still needed figuring out: 1. something must be in the atom to balance the charge 2. atoms must have some type of particle to produce so much mass Sep 168:27 AM Sep 272:39 PM Ernest Rutherford The Nucleus • In 1911, Ernest Rutherford studied how positively charged alpha particles interacted with solid matter. (with Geiger and Marsden) The Gold Foil Experiment • By aiming the particles at a thin sheet of gold foil, Rutherford expected the paths of the alpha particles to be only slightly altered by a collision with an electron. 1. discovered the nucleus 2. nucleus was very small yet packed with matter 3. nucleus was + Sep 272:39 PM The Nucleus (cont.) Sep 168:30 AM The Nucleus (cont.) • Rutherford refined the model to include positively charged particles in the nucleus called protons. • All atoms are made of three fundamental subatomic particles: the electron, the proton, and the neutron. • James Chadwick received the Nobel Prize in 1935 for discovering the existence of neutrons, neutral particles in the nucleus which accounts for the remainder of an atom’s mass. • Atoms are spherically shaped. • Atoms are mostly empty space, and electrons travel around the nucleus held by an attraction to the positively charged nucleus. Sep 272:41 PM Sep 272:42 PM 5 ch 4 notes sept 30 oct 1.notebook October 01, 2013 The Nucleus (cont.) • Scientists have determined that protons and neutrons are composed of subatomic particles called quarks. Section 4.2 Assessment Atoms are mostly ____. A. positive B. negative C. solid spheres D. empty space • • • • A B C D • Chemical behavior can be explained by considering only an atom's electrons. Section 42 Sep 272:42 PM Sep 2711:11 AM Section 4.3 How Atoms Differ What are the two fundamental subatomic particles found in the nucleus? A. proton and electron B. proton and neutron C. neutron and electron D. neutron and positron • • • • A B C D • Explain the role of atomic number in determining the identity of an atom. • Define an isotope. • Explain why atomic masses are not whole numbers. • Calculate the number of electrons, protons, and neutrons in an atom given its mass number and atomic number. periodic table: a chart that organizes all known elements into a grid of horizontal rows (periods) and vertical columns (groups or families) arranged by increasing atomic number atomic number isotopes mass number atomic mass unit (amu) atomic mass Section 42 Sep 2711:11 AM Let's focus on the PROTONS: What is going on inside the nucleus? Protons: p+ opposite the charge of an electron Sep 272:44 PM Atomic Number Neutrons: no high energy particles with no charge same mass as proton quarks, gluons, mesons... • Each element contains a unique positive charge in their nucleus. • The number of protons in the nucleus of an atom identifies the element and is known as the element’s atomic number. Nuclear forces: shortrange p/n, p/p and n/n forces that make them sticky Sep 168:31 AM Oct 18:54 AM 6 ch 4 notes sept 30 oct 1.notebook October 01, 2013 # OF PROTONS = IDENTITY Z = atomic number 47 • All atoms of a particular element have the same number of protons and electrons but the number of neutrons in the nucleus can differ. Ag average atomic mass 107.8682 Sep 168:36 AM Sep 272:46 PM Remember this guy? • Atoms with the same number of protons but different JJ Thomson numbers of neutrons are called isotopes. * he was the first to discover that • Adding the # of protons to the # neutrons = atoms of neon could have different masses. Neon-22 Neon-20 MASS NUMBER (A) * he was the first to discover the existence of stable isotopes Oct 18:58 AM Oct 19:05 AM ISOTOPES # of Neutrons =determines which isotope Isotope Protium hyphen notation # protons 1 # neutrons 0 Mass number 1 Nuclide Hyphen symbol notation 1 H Hydrogen-1 H Hydrogen-2 1 2 nuclide symbol Deuterium 1 1 2 1 3 A X Hydrogen1 Z 1 name of element mass number (A) Sep 168:36 AM 1 Tritium 1 2 3 1 H Hydrogen-3 H Oct 13:50 PM 7 ch 4 notes sept 30 oct 1.notebook October 01, 2013 Although isotopes have different masses, they do not differ significantly in their chemical behavior. Isotopes of the same element can have different uses: Sep 272:46 PM Oct 19:11 AM Relative atomic mass: use carbon12 as the standard Mass of Atoms • One atomic mass unit (amu) is defined as 1/12th the mass of a carbon12 atom. atomic mass units • One amu is nearly, but not exactly, equal to one proton and one neutron. • When we are talking about the mass of ONE atom, we label it as amu. Carbon12 = 12 amu Sep 168:40 AM Sep 272:46 PM Carbon14 Carbon13 Halflife = 5730 years Natural abundance Isotopic tracing Notice that isotopes of the same for metabolism radioactive dating Sep 178:19 AM element do NOT occur in the same amounts in nature. Oct 19:16 AM 8 ch 4 notes sept 30 oct 1.notebook October 01, 2013 For the isotope Mg-24: The actual mass of Mg-24 is a) Find the # of protons, electrons and neutrons atomic mass is 23.985 042 amu b) Using the number of protons, neutrons and electrons, calculate WHY???????????? the mass of an atom of Mg-24: Oct 110:24 AM Oct 110:26 AM Calculating the average atomic mass on * Protons and neutrons are not exactly 1 amu the periodic table Isotope * electrons have mass 6 * small amount of mass is changed to energy in the creation of a nucleus 7 X X mass (amu) 6.015 7.59% 7.016 92.41% Sep 168:42 AM Oct 18:03 AM Calculate the average atomic mass of Isotope % natural abundance Atomic Mass (amu) Copper63 Copper65 69.17% 30.83% 62.929 599 64.927 793 magnesium: Isotope atomic mass % abundance % abundance Mg-24 23.985 78.99% Mg-25 24.986 10.00 Mg-26 25.983 11.01 Average atomic mass? Oct 110:27 AM Sep 168:48 AM 9 ch 4 notes sept 30 oct 1.notebook October 01, 2013 Section 4.3 Assessment Elements with the same number of protons and differing numbers of neutrons are known as what? A. isotopes B. radioactive C. abundant D. ions • • • • A B C D An unknown element has 19 protons, 19 electrons, and 3 isotopes with 20, 21 and 22 neutrons. What is the element’s atomic number? A. 38 B. 40 C. 19 D. unable to determine • A • B • C • D Section 43 Sep 2711:11 AM Section 43 Sep 2711:11 AM 10