Ch 5 Packet - CHAPTER 5 ATOMIC THEORY The Nuclear Model of...

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Chemistry 139 Fall 2009 page 1 CHAPTER 5: ATOMIC THEORY: The Nuclear Model of the Atom Problems: 1-2, 9, 13, 15, 17, 19, 21, 25, 27, 29, 31, 34, 35, 37, 39, 43, 45 DALTON’S ATOMIC THEORY 1. An element is composed of tiny, indivisible* particles called atoms. 2. All atoms of an element are identical* and have the same properties. 3. Atoms of one element will differ from atoms of another element. 4. Compounds contain atoms in small whole number ratios. e.g., each water molecule (H 2 O) has one O atom and 2 H atoms 5. Atoms can combine to form different compounds. e.g., carbon and oxygen can combine to form CO 2 or CO * Later proven wrong SUBATOMIC PARTICLES Michael Faraday, William Crookes, and many other scientists carried out experiments discovery of electrons (e ) , tiny negatively charged subatomic particles J.J. Thomson was given credit for discovering electron although evidence had accumulated for 20 years before his group’s determination of the electron’s charge and mass. Eugen Goldstein (late 1880s) – carried out experiments on canal rays and found they consisted of positively charged subatomic particles discovery of protons (p + ) And decades later, James Chadwick won the Nobel Prize winner for his discovery (1935) neutron (n) = neutral subatomic particle Atoms are made up of subatomic particles: electron (e ): negatively charged subatomic particle (charge = –1) proton (p + ): positively charged subatomic particle (charge = +1) neutron (n) = neutral subatomic particle (charge=0) Particle Symbol Location Charge Relative Mass (amu) electron e outside nucleus –1 1/1836 ≈ 0 proton p + inside nucleus +1 1 neutron n inside nucleus 0 1
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Chemistry 139 Fall 2009 page 2 THE NUCLEAR ATOM PLUM-PUDDING MODEL OF THE ATOM Thomson proposed that the atom was a uniform sphere of positively charged matter in which electrons were embedded electrons are like raisins in a pudding of protons proton charge is very diffuse, spread out electron charge is concentrated in tiny spots Evidence: X-rays and radiation can travel through solids THE NUCLEAR ATOM: PROTONS AND THE NUCLEUS Ernest Rutherford was a scientist who did many pioneering experiments in radioactivity He had members of his research group test Thomson’s Plum-Pudding Model using radioactive alpha ( ) particles, basically helium atoms with a +2 charge and much bigger
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Ch 5 Packet - CHAPTER 5 ATOMIC THEORY The Nuclear Model of...

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