Lecture_3 - Today's Lecture Atoms, Molecules and Ions 2.6...

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1 Atoms, Molecules and Ions Today’s Lecture 2.6 The Modern View of Atomic Structure 2.7 Molecules and Ions 2.8 An Introduction to the Periodic Table 2.9 Naming Simple Compounds 1 Modern View of Atomic Structure ± the simplest view of the atom: ± consists of a tiny nucleus with a diameter of ~ 10 -13 cm ± electrons move about the nucleus at an average distance of about ~ 10 -8 cm Figure 2.13 2 ± the nucleus is assumed to contain protons (positively charged particles) and neutrons (neutral particles) ± how do we know this?
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2 Atomic Structure (cont’d) ± the mass and charge of the electron, proton and neutron Particle Mass Charge Electron 9.11 x 10 -31 kg -1 Proton 1.67 x 10 -27 kg +1 Neutron 1.67 x 10 -27 kg 0 ± note that the magnitude of the electron and the proton chargeis1 .60x10 -19 C 3 ± summary: ± the nucleus is small relative to the overall size of the atom but it has a huge mass relative to the total mass of the atom (i.e. the nucleus has an extremely high density) Atomic Structure (cont’d) ± chemists are generally satisfied with a relatively crude picture of the nucleus ± why? ± another question ± “if all atoms are made up of these same components (electrons, protons and neutrons), why do different tmsh diff thmi l ti s?” 4 atomshavedifferentchemicalproperties?”
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3 Notation for Atoms ± where X A Z ± X = element symbol (e.g. H, He, Li, etc.) ± Z = atomic number = # of protons = # of electrons ± A = mass number = (# of protons + # of neutrons) ± # of neutrons = (A - Z) 5 ± e.g. He 4 2 Isotopes ± a l latomsofthesamee lementhavethesamenumberof protons and electrons but they can have different numbers of neutrons ± atoms of the same element with different number of neutrons are called isotopes ± e.g. there are 3 isotopes for hydrogen ± protium H 1 1 6 ± deuterium ± tritium H 2 1 H 3 1
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4 Isotopes (cont’d) ± in nature, most elements contain a mixture of isotopes: ± e.g. Carbon (C) carbon 12 (98 892% ± carbon-12 (98.892%) ± carbon-13 (1.108) ± carbon-14 (negligible) ± e.g. Silicon (Si) ± silicon-28 (92.23%) Why do isotopes of a particular element show almost identical chemical properties? 7 ± silicon-29 (4.67%) ± silicon-30 (3.10%) ± e.g. Rubidium (Rb) ± rubidium-85 (72.17%) ± rubidium-87 (27.83%) Isotopes (cont’d) Pt (atomic number 78) Tc (atomic number 43) ± for some elements, several isotopes exist (e.g. platinum) ± mass number 190 (0.014%) ± mass number 192 (0.782%) ± mass number 194 (32.967%) ± mass number 195 (33.832%) ± mass number 196 25 242% ±
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Lecture_3 - Today's Lecture Atoms, Molecules and Ions 2.6...

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