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week03

# week03 - CH 2 Atoms ions and the periodic table Daltons...

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1 CH 2. Atoms, ions and the periodic table Dalton’s Atomic Theory Structure of the Atom • Ions Atomic Mass – Math toolbox 1.1 (pp. 36 - 37) The Periodic Table Dalton’s ( modern ) Atomic Theory Dalton’s Atomic Theory has 4 postulates: 1. All matter is composed of exceedingly small, indivisible particles called atoms . 2. All atoms of a given element are identical both in mass and in chemical properties . However, atoms of different elements have different masses and different chemical properties. 3. Atoms cannot be created or destroyed in chemical reactions. 4. Atoms combine in simple, fixed, whole-number ratios to form compounds. This was proven wrong later - see isotopes Structure of the Atom – “Nuclear Atom” Atom is divisible and made of subatomic particles Subatomic particles include: – Electrons: outside nucleus; negatively charged – Particles in the nucleus • Protons: positively charged • Neutrons: uncharged

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2 The Discovery of Electrons (1897) Figure 2.5 J.J. Thomson proved The existence of electron Negative charge “Pudding” model ( incorrect ) Charge/mass ratio Charge by oil drop experiment (Millikan, see p.58) Rutherford: The Nuclear Atom Subatomic Particles ( Table 2.1, p.60 ) Proton ( p ): – Q = +1.6022 x 10 -19 C (expressed as +1 ) m = 1.6726 x 10 -24 g ( hydrogen atom ) Neutron ( n ): – no charge m = 1.6749 x 10 -24 g • Electron ( e ): – Q =- 1.6022 x 10 -19 C (expressed as - 1 ) m = 9.1094 x 10 -28 g (1/1836 of a H atom) No need to memorize numeric values of masses and charges; but need to know the “relative” values in red
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week03 - CH 2 Atoms ions and the periodic table Daltons...

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