Chemistry Atomic Theories Part 1 PDF

Chapter Outline 2.1 Imaging and Moving Individual Atoms 2.2 Early Ideas about the Building Blocks of Matter 2.3 Modern Atomic Theory and the Laws That Led to It 2.4 Atomic Structure 2.5 Atomic Mass: The Average Mass of an Element’s Atoms Skipping 2.6 (chemistry 30) 2.7 The Periodic Table of the Elem...

Chapter Outline 2.1 Imaging and Moving Individual Atoms 2.2 Early Ideas about the Building Blocks of Matter 2.3 Modern Atomic Theory and the Laws That Led to It 2.4 Atomic Structure 2.5 Atomic Mass: The Average Mass of an Element’s Atoms Skipping 2.6 (chemistry 30) 2.7 The Periodic Table of the Elements Copyright © 2023 Pearson Canada Inc. 2-1 2.1 Imaging and Moving Individual Atoms measuring how an electrical current—flowing between a sharp metal tip and a flat metal surface—varied as the distance between the tip and the surface varied 1981, Gerd Binnig and Heinrich Rohrer IBM in Zurich, Switzerland. 1986, joint Nobel Prize in Physics Figure 2.1 Scanning Tunnelling Microscopy Copyright © 2023 Pearson Canada Inc. 2-2 Imaging Atoms If all the words in Library and Archives Canada in Ottawa—20 million books— were written in letters the size of these Kanji characters, they would fit in an area of about 3.5 square millimetres. Figure 2.2 Imaging Atoms [(a) Veeco Instruments, Inc.; (b) IBM Research Division] Copyright © 2023 Pearson Canada Inc. 2-3 2.2 Early Ideas about the Building Blocks of Matter th 5 Century BC Leucippus and Democritus – atomos Aristotle and Plato – earth, air, fire and water 16th Century The Scientific Revolution Copernicus, Bacon, Kepler, Galileo, Boyle, Newton - the scientific method became the established way to learn about the physical world. 17th Century Dalton – atomic theory Copyright © 2023 Pearson Canada Inc. 2-4 2.3 Modern Atomic Theory and the Laws That Led to It The Law of Conservation of Mass In a chemical reaction, matter is neither created nor destroyed. 1789, Antoine Lavoisier Who’s hand is this? Marie-Anne Pierrette Paulze Lavoisier, later Countess von Rumford French chemist and noblewoman pivotal role in the translation of several scientific works standardization of the scientific method Copyright © 2023 Pearson Canada Inc. 2-5 Reaction between Sodium Metal and Chlorine Gas to Form Sodium Chloride [Na and Cl: Charles D. Winters/Science Source; NaCl: Joseph Calev/Shutterstock] Copyright © 2023 Pearson Canada Inc. 2-6 Law of Definite Proportions 1797, French chemist Joseph Proust All samples of a given compound, regardless of their source or how they were prepared, have the same proportions of their constituent elements. Mixture components can be present in whatever ratios. Decompose 18.0 g of water. You will get 16.0 g of oxygen and 2.0 g of 16 𝑔 8 hydrogen, or an oxygen-to-hydrogen mass ratio of 2 𝑔 = 1 hints at the idea that matter might be composed of atoms. Compounds have definite proportions of their constituent elements because the atoms that compose them, each with its own specific mass, occur in a definite ratio. Copyright © 2023 Pearson Canada Inc. 2-7  John Dalton, British chemist Law of Multiple Proportions (1 of 2) When two elements (A and B) form two different compounds, the masses of B that combine with 1 g of element A can be expressed as a ratio of small whole numbers. Dalton already suspected that matter was composed of atoms when two elements, A and B, combined to form more than one compound, an atom of A combined with either one, two, three, or more atoms of B (AB1,AB2,AB3, etc.). the ratio of the masses of B that reacted with a fixed mass of A would always be a small whole number Copyright © 2023 Pearson Canada Inc. 2-8 Law of Multiple Proportions (2 of 2) Mass of O to 1 g C in CO 2 2.67 = = 2.0 Mass of O to 1 g C in CO 1.33 Copyright © 2023 Pearson Canada Inc. 2-9 Overview of the atomic theory https://www.youtube.com/watch?v=xazQRcSCRaY Copyright © 2023 Pearson Canada Inc. 2 - 10 John Dalton and the Atomic Theory 1. Each element is composed of tiny, indestructible particles called atoms. 2. All atoms of a given element have the same mass and other properties that distinguish them from atoms of other elements. 3. Atoms combine in simple, whole-number ratios to form compounds. 4. Atoms of one element cannot change into atoms of another element. In a chemical reaction, atoms only change the way they are bound together with other atoms. Copyright © 2023 Pearson Canada Inc. 2 - 11  English physicist J. J. Thomson (1856– 1940) 2.4 Atomic Structure Discovery of the Electron Figure 2.3 Cathode Ray Tube [© Richard Megna/Fundamental Photographs, NYC] Copyright © 2023 Pearson Canada Inc. 2 - 12 Cathode Ray Tube Experiment glass tube called a cathode ray tube The tube was partially evacuated, (much of the air was pumped out of the tube because air interferes with cathode rays). applied a high electrical voltage between two electrodes at either end of the tube. found that a beam of particles, called cathode rays, travelled from the negatively charged electrode (which is called the cathode) to the positively charged one (called the anode). Copyright © 2023 Pearson Canada Inc. 2 - 13 Electrons Thomson found that these particles had the following properties: they travelled in straight lines, they were independent of the composition of the material from which they originated (the cathode), and they carried a negative electrical charge. Copyright © 2023 Pearson Canada Inc. 2 - 14 Characteristics of Electrical Charge Electrical charge is a fundamental property of some of the particles that compose atoms. It results in attractive and repulsive forces—called electrostatic forces—between those particles. The area around a charged particle where these forces exist is called an electric field. Copyright © 2023 Pearson Canada Inc. 2 - 15 Charge-to-Mass Ratio e /m = –1.76 108 C/g Figure 2.4 Thomson’s Measurement of the Charge-to-Mass Ratio of the Electron Copyright © 2023 Pearson Canada Inc. 2 - 16 Charge-to-Mass Ratio cont. electric and magnetic fields to deflect the electron beam in a cathode ray tube measured the strengths at which the effects of the two fields (electric and magnetic) cancelled exactly and make the beam undeflected (going straight) was able to calculate the charge-to-mass ratio of the electron. Copyright © 2023 Pearson Canada Inc. 2 - 17 Milikan’s Oil Drop Experiment 1909, American physicist Robert Millikan e = –1.6 10 –19 C Figure 2.5 Millikan’s Measurement of the Electron’s Charge Copyright © 2023 Pearson Canada Inc. 2 - 18 Oil Drop Experiment sprayed oil into fine droplets using an atomizer. The droplets were allowed to fall under the influence of gravity through a small hole into the lower portion of the apparatus with a microscope looking in During their fall, the drops acquired electrons that had been produced by bombarding the air in the chamber with ionizing radiation Drops have now negative charge an electric field between two metal plates. Since the lower plate was negatively charged, and since Millikan could vary the strength of the electric field, the free fall of the negatively charged drops could be slowed and even reversed Copyright © 2023 Pearson Canada Inc. 2 - 19 Oil Drop Experiment cont. Measured the size of the electric field required to halt the free fall of the drops determined the masses of the drops themselves (from their radii and density), Millikan calculated the charge of each drop. Each drop must contain an integral (or whole) number of electrons, the charge of each drop must be a whole- number multiple of the electron’s charge. the measured charge on any drop was always a whole- number multiple of 1.60×10−19 C the fundamental charge of a single electron Copyright © 2023 Pearson Canada Inc. 2 - 20 Calculating the Mass of an Electron e /me = −1.76  108 C/g from Thomson’s cathode ray tube e = −1.6  10−19 C from Millikan’s oil drop experiment mass charge  = mass charge −19 1g −28 me = −1.6  10 C = 9.1  10 g −1.76  10 C 8 Copyright © 2023 Pearson Canada Inc. 2 - 21