Ch5 notes - Atoms and Subatomic Particles Chapter 5...

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1 Atoms and Subatomic Particles Chapter 5 § Element: a pure substance that cannot be broken down into simpler pure substances § Compound: a pure substance that can be broken down to two or more simpler substances § Atom: the smallest particle of an element that still has the properties of the element
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2 John Dalton 19th century Experimental observations: - most natural materials are mixtures of pure substances -pure substances are either elements or compounds -a given compound always contains the same proportion, by mass of the elements (The law of definite proportions) e.g.: water always contains 8 grams of oxygen for every 1 gram of hydrogen
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3 Dalton’s Atomic Theory (original early 1800’s) (Atomic Theory of Matter) pg. 130 Modern Version w All matter is made up of small, neutral particles called atoms. There are 117 different types of atoms. Each type corresponds to a different element. w All atoms of a given element are similar to one another. w Atoms of a given element are different from those of any other element. w Atoms of one element combine with atoms of other elements to form compounds. w A compound always has the same relative numbers and types of atoms. w During a chemical reaction, changes occur only in the way atoms are grouped together ie: atoms are neither created nor destroyed in chemical reactions
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4 Prediction: Atoms of a given pair of elements could combine in different proportions and produce different compounds. e.g: N nitrogen and O oxygen 1 : 1 NO nitric oxide, colourless gas 1 : 2 NO 2 nitrogen dioxide, brown gas 2 : 1 N 2 O nitrous oxide, colourless gas, (laughing gas) 3 different pure substances (compounds) each with its own distinct set of chemical and physical properties but made up from the same two elements.
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5 Charge § A piece of amber rubbed with cloth will attract some objects to it and repel others. § A glass rod rubbed with silk will attract some objects and repel others. § The glass rod will repel other glass rods that have been rubbed with silk; the amber will repel other pieces of amber that have been rubbed with cloth. The glass rod and the amber will attract each other. § The amber and the glass rod have become “charged” § By convention the amber is assigned a NEGATIVE charge. § The glass rod has a POSITIVE charge § Like charges repel, opposite charges attract
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6 Structure of the Atom -Subatomic Particles Electrons: 1890’s J. J. Thomson observations: -atoms of any element could be made to emit tiny negative particles -same (-) ve particle no matter which element conclusion: - all atoms contain negative particles (called electrons), that have almost negligible mass
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This note was uploaded on 05/12/2011 for the course CHEM 110 taught by Professor Sophielavieri during the Fall '09 term at Simon Fraser.

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Ch5 notes - Atoms and Subatomic Particles Chapter 5...

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