Chapter_02-Atoms_Molecules_Ions

Chapter_02-Atoms_Molecules_Ions - Chapter 2. Atoms,...

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Chapter 2. Atoms, Molecules and Ions Chapter 2. Atoms, Molecules and Ions Atoms Atoms Non-destructable substances = Elemental substances; Pure compounds consist from a certain relative masses of elements (water = 1 part of hydrogen and 8 parts of oxygen); Idea of elemental substances + idea of atoms atomic theory of matter. John Dalton: 1) Each element is composed of atoms; 2) All atoms of an element are identical; 3) Atoms of one element do not change into another and atoms cannot be destroyed or disappear (in chemical reactions). 4) Compounds are formed from different elements with certain relative number of different atoms . History
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Chapter 2. Atoms, Molecules and Ions Chapter 2. Atoms, Molecules and Ions Atoms Atoms J.J. Thomson: Cathode rays are deflected in electric and magnetic fields, and this is independent from the cathode material discovery of electron, i.e. a negative particle with 1.76*10 8 C/g (coulombs per gram) that is present in all substances. R. Millikan: An electric charge acquired by an oil droplet is always an integral multiples of 1.60*10 -19 C Mass of electron = 9.10*10 -28 g. Discovery of electron
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Chapter 2. Atoms, Molecules and Ions Chapter 2. Atoms, Molecules and Ions Atoms Atoms Three rays of radioactivity E. Rutherford: Radioactive matter emits: light negative (electrons) – beta rays; heavy positive particles – alpha rays; some neutral non-particles – gamma rays As these particles never were observed in chemical reaction, it was supposed that they come from inside of an atom.
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Chapter 2. Atoms, Molecules and Ions Chapter 2. Atoms, Molecules and Ions Atoms Atoms How do electrons (negative charge) the positive charge coexist in atom? Thomson’s “plum- pudding” model Basic idea: negative charge and positive charge attract each to other, therefore they must be close each to other inside atom. Rutherford’s “nucleus” model comes from alpha-particles scattering experiment. The fact that some of angles of scattering are very big tells that all positive charge is concentrated in a volume much smaller than atom – nucleus.
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Chapter 2. Atoms, Molecules and Ions Atoms Atoms Parts of atom Almost all mass of an atom is concentrat ed in nucleus Electric charge = 0 Mass = 1.0087 amu Electric charge = +1; Mass = 1.0073 amu Electric charge = -1; Mass = 5.486*10^(-4) amu For convenience the electric charge and mass of atomic particles can be expressed in electronic charge [e] and atomic mass unit [amu] , but these are not SI units. Converting to SI system (to C and kg): 1 e = 1.60*10^(-19) C; {symbol e often is omitted}. • 1 amu = 1.66*10^(-27 kg); | | | 1-5 Å (Angstrom) | | 1 Å = 10^(-10)m | Typical size of an atom •1 amu is roughly a mass of a hydrogen atom (precise value is 1/12 part of the mass of carbon atom). 1 e is a absolute value of
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This note was uploaded on 01/02/2012 for the course CHEM 114 taught by Professor Sergeiaksyonov during the Fall '11 term at ASU.

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Chapter_02-Atoms_Molecules_Ions - Chapter 2. Atoms,...

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