Ochem_UNIT_2 - OCHEMUNIT2:STRUCTUREANDBONDING A...

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OCHEM   UNIT 2: STRUCTURE AND BONDING A. ATOMIC STRUCTURE: A REVIEW 1. MODERN VIEW ON THE MICROSCOPIC STRUCTURE OF  MATTER 2. SOME DEFINITIONS atomic number (Z)  = number of protons in the nucleus of an atom. Ex. mass number (A)  = protons + neutrons. Ex. symbol of an atom Ex.   Isotopes  = atoms of the same element with different mass numbers 1
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Ex. See Figure on page 9. atomic weight of X = average weight or mass of all isotopes of a given  element X. Ex.  Note : in the  neutral atom , number of electrons = number of protons cation  = positive ion Ex. anion = negative ion Ex. B. THE PERIODIC TABLE 1. INTRODUCTION - discovered by Mendeleev and Lothar Meyer in 1869 -column = group or family      = elements have similar chemical and physical properties -row = period 2
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2. IMPORTANT ELEMENTS IN OCHEM C, H, O, Si, S, P, Li, Na, Mg, K, and halogens . See Fig. 1.2 Page 10. C. ATOMIC STRUCTURE: THE SHELL MODEL AND  ORBITALS 1. INTRODUCTION -From wave mechanics, electrons in atoms are in energy levels called shells.  In a summary: Shell  subshells orbitals (electron densities) 2. TYPES OF SUBSHELLS a.  s subshells -spherical -one s orbital -can take up to 2 electrons b. p subshells -spherical lobes or dumbbell shape -set of 3 degenerate orbitals (Px, Py, Pz) in a given subshell -can take up to 6 electrons c. d subshells -various shapes -set of 5 d orbitals in a given subshell -can take up to 10 electrons d. f subshells 3
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-various shapes -set of 7 f orbitals in a given subshell -can take up to 14 electrons See Fig. on page 11. Note: Only s and p orbitals are involved in OChem Recall: A node = region with zero electron density. 3. ELECTRON CONFIGURATION EC = Electron distribution in atom Filling order 1s 2s 2p 3s 3p 4s 3d 4p………… Ex. Do Problem 1.1 and 1.2 page 12  D. THE NATURE OF THE CHEMICAL BOND    1. INTRA AND INTERMOLECULAR FORCES: A REVIEW -Intermolecular forces = ion-dipole, dipole-dipole, H bonds, London  Dispersion Forces (or van der Waals’ Forces): determine physical properties -Intramolecular forces = ionic bonds, covalent bonds, coordinate covalent  bonds, metallic bonds: determine chemical properties Note: covalent bonds are the bonds mostly encountered in organic  compounds. 4
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Recall: metal + nonmetal = ionic compound nonmetal + nonmetal = covalent or molecular compound. 2. VALENCE SHELL ELECTRONS -Outermost shell electrons Ex: Na, Cl, Ne Note: only valence electrons are involved in chemical reactions.
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