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Transcript
History of the Atom March 31, 2015 What's Going On? Your Atomic Theory The Atomic Theory A Summary of the Atom Learning Goal I will be able to describe the evolution of The Atomic Theory. 1 History of the Atom March 31, 2015 Your Atomic Theory Based on the information presented on the first 18 elements, come up with your own "atomic theory" by answer the following questions. a. What makes up an atom? b. What does an oxygen atom look like? 2 History of the Atom March 31, 2015 Dalton's Spheres Modern atomic theory began to take shape in the early 1800s. John Dalton reconsidered the ancient idea that each different kind of element is composed of a different kind of atom. 3 History of the Atom March 31, 2015 Dalton's Spheres He imagined that all atoms were like small spheres with different properties. He assumed they might vary in size, mass or colour. 4 History of the Atom March 31, 2015 Dalton's Spheres Dalton's Theory 1. All matter is made of small, indivisible particles called atoms. 2. All atoms of an element are identical in properties such as size and mass. 3. Atoms of different elements have different properties. 4. Atoms of different elements can combine in specific ways to form new substances. 5 History of the Atom March 31, 2015 Dalton's Spheres Dalton also devised a series of element symbols to represent the atoms of different elements. 6 History of the Atom March 31, 2015 Thomson's Electrons J.J. Thomson, an English physicist, researched the idea that atoms might be made from a combination of particles. He experimented with electric currents in glass tubes called cathode ray tubes. 7 History of the Atom March 31, 2015 Thomson's Electrons He was able to cause nonradioactive atoms to produce streams of negatively charged particles. 8 History of the Atom March 31, 2015 Thomson's Electrons Because all of the elements Thomson tested produced electrons, he reasoned that the atoms of all elements contain electrons. Thomson proposed a new model for atoms in 1897 in which each atom was composed of smaller particles. 9 History of the Atom March 31, 2015 Thomson's Electrons Because Thomson had detected negatively charged particles, he reasoned that because atoms have no overall charge, they must also contain positive charges. Thomson imagined the atom as a positive sphere with negative electrons scattered throughout it. 10 History of the Atom March 31, 2015 Rutherford's Nuclei Ernest Rutherford tested Thomson's model by shooting positively charged particles at a thin gold foil. 11 History of the Atom March 31, 2015 Rutherford's Nuclei In the experiment, most of the highspeed positive particles went through the foil, but about 1 in 10 000 bounced back as if deflected by something very massive and positively charged. 12 History of the Atom March 31, 2015 Rutherford's Nuclei He had discovered the nucleus, the centre of the atom! This tiny positively charged part of the atom also contains most of the atom's mass. 13 History of the Atom March 31, 2015 Rutherford's Nuclei Rutherford revised the model and predicted that all atoms contained a nucleus. His model resembled Thomson's but all of the atom's positive charge was concentrated at a tiny point in the centre. 14 History of the Atom March 31, 2015 Rutherford's Nuclei James Chadwick (Rutherford's student), refined the concept of the nucleus. He discovered that the nucleus contains neutral particles called neutrons as well as protons. These neutrons are similar in size to protons but carry no charge. 15 History of the Atom March 31, 2015 Bohr's Energy Levels Niels Bohr transformed Rutherford's model into the model we use today. Below are two "Bohr Diagrams" showing a simplified version of Bohr's model. 16 History of the Atom March 31, 2015 Bohr's Energy Levels Bohr suggested that electrons surround the nucleus in specific energy levels, called shells. He discovered that electrons jump between these shells by gaining or losing energy, and that each shell can contain a limited number of electrons. The first three shells are known to be able to hold two, eight and eight electrons. 17 History of the Atom March 31, 2015 The Quantum Mechanical Model The most advanced, and accurate, model of the atom describes electrons as not existing as tiny points inside an atom. Instead, electrons exist in energy levels and surround the positively charged nucleus in a form resembling a cloud. 18 History of the Atom Dalton Early 1800s March 31, 2015 Thomson 1897 Rutherford 1899 Chadwick 1932 Bohr 1915 Quantum Mechanical Model 19 History of the Atom March 31, 2015 How Big is an Atom? Video! 20 History of the Atom March 31, 2015 A Summary of the Atom All elements of composed of __________, and one ________ is the smallest unit of any element. Atoms are made of different kinds of smaller particles, called __________________ particles. They exist in three types: ______________, ________________ and __________________. 21 History of the Atom March 31, 2015 A Summary of the Atom Each type of subatomic particle has what is known as a relative mass. As the least massive, __________________ are given a relative mass of 1. 22 History of the Atom March 31, 2015 23 Attachments 1D CHEM B1 (History of the Atom) Atomic Theory.mp4
