Chapter2 - Chapter 2 Atoms Molecules Ions 2.1 Atomic Theory Democritus(5th century BC matter is composed of indivisible particles call atomos

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Chapter 2: Atoms, Molecules, Ions 2.1 Atomic Theory Democritus (5 th century BC) - matter is composed of indivisible particles call atomos Alchemists (100 - 1600 A. D.) - made many discoveries while pursuing metaphysical goals Robert Boyle (17th century) - quantitative measurements of the properties of matter Joseph Priestley and Antoine-Laurent Lavoisier (18 th century) - showed that combustion is a reaction between matter and oxygen John Dalton - Atomic Theory (ca. 1808) 1. Elements are composed of extremely small particles call atoms. All atoms of a given element are identical, having the same size, mass, and chemical properties. The atoms of one element are different from the atoms of all other elements. (Fig.2.1, p. 36) 2. Compounds are composed of atoms of more than one element. In any compound, the ratio of the numbers of atoms of any two of the elements present is either and integer or a simple fraction. ( incorporates laws of definite proportions and multiple proportions ) Law of definite proportions - different samples of the same compound always contain its constituent elements in the same proportions by mass. Law of multiple proportions - If two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in ratios of small whole numbers (use CO and CO 2 as an example: 12 to 16 versus 12 to 32.) Law of conservation of mass - matter can be neither created nor destroyed. 3. A chemical reaction involves only the separation, combination, or rearrangement of atoms; it does not result in their creation or destruction.
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2 Chapter 2 Chem 1303 2.2 The Structure of an Atom An atom is the basic unit of an element that can enter into chemical combinations. But what is an atom made of: Order of discovery: Cathode Ray tube (Figure 2.3) charge to mass ratio -1.76 × 10 8 coulomb/g Millikan Oil drop experiment charge of electron = -1.60 × 10 -19 coulombs mass of the electron is 9.09 × 10 -28 g (very small !) Atoms are composed of electrons negatively charged mass = 9.1096 × 10 -31 kg proton s positively charged mass = 1.6727 × 10 -27 kg neutrons neutral mass = 1.6750 × 10 -27 kg Radioactivity - Radioactive substances emit 3 kinds of particles and/or radiation alpha ( α ) particles (helium nuclei) beta ( β ) particles (electrons) gamma ( γ ) rays Radioactive Particles (Fig. 2.6) Rutherford experiment (Fig. 2.8) relate to α particles Proton
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3 Chapter 2 Chem 1303 Proton Ernest Rutherford discovered that the positive charge was not spread out over the entire volume of the atom but was concentrated in a small, very dense core (the nucleus). Have the same but opposite charge as the electrons, but
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This note was uploaded on 08/22/2011 for the course CHEM 101 taught by Professor C during the Spring '11 term at University of Texas at Dallas, Richardson.

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Chapter2 - Chapter 2 Atoms Molecules Ions 2.1 Atomic Theory Democritus(5th century BC matter is composed of indivisible particles call atomos

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