Atomic Structure. Atomic weight = m protons + m neutrons Atomic number (Z) = # of protons Isotope corresponds to # of neutrons

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1 Atomic Structure Neutrons: neutral Protons: positive charge (1.6x10 19 C, 1.67x10 27 kg) Electrons: negative charge (1.6x10 19 C, 9.11x10 31 kg) Atomic weight = m protons + m neutrons Atomic number (Z) = # of protons Isotope corresponds to # of neutrons 1 mole = 6.023x10 23 atoms (Avogadro s number) 6

2 Quantum Mechanic: Bohr Atom orbital electrons: n = principal quantum number n=3 2 1 Nucleus: Z = # protons = 1 for hydrogen to 94 for plutonium N = # neutrons 7

3 Quantum Mechanic: Wave Mechanics Quantum Numbers Principle quantum number n = K, L, M, N, O, Subsidiary quantum number or Subshell l = s, p, d, f Magnetic quantum number or Energy States m l = 1, 3, 5, 7 Electron spin quantum number or Spin Moment m s = +½, ½ Structure of an atom = Electron Configuration Electrons occupy the outermost filled shell = Valence Electrons 8

4 Electron Energy States Electrons have discrete energy states tend to occupy lowest available energy state Increasing energy n=4 n=3 n=2 n=1 4s 3s 2s 1s 4p 3p 2p 3d 9

5 Expected Electron Configurations Element ydrogen elium Lithium Beryllium Boron Carbon... Neon Sodium Magnesium Aluminum... Argon... Krypton Atomic # Electron configuration 1s 1 1s 2 (stable) 1s 2 2s 1 1s 2 2s 2 1s 2 2s 2 2p 1 1s 2 2s 2 2p s 2 2s 2 2p 6 (stable) 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 3s 2 1s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p 6 (stable)... 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s (stable) 10

6 give up 1e give up 2e give up 3e Li Be Na K Rb Cs Fr Mg Ca Sr Ba Ra Sc Y The Periodic Table Metal Nonmetal Intermediate accept 2e accept 1e O S Se Te Po F Cl Br I At inert gases e Ne Ar Kr Xe Rn Electropositive elements: Readily give up electrons to become + ions. Electronegative elements: Readily acquire electrons to become ions. 11

7 Bonding Forces and Energies E = F dr 12

8 Type of Bonding Primary or Chemical Bonds Ionic Bonding Covalent Bonding Metallic Bonding Secondary or Physical (van der Waals) Bonds Fluctuating induced dipole bonds Polar molecule induced dipole bonds Permanent dipole bonds 13

9 Chemical Bonds: Ionic Bonding Occurs between + and ions Requires electron transfer Large different electronegativity required Example: NaCl Na (metal) unstable Na (cation) stable electron + Coulombic Attraction Cl (nonmetal) unstable Cl (anion) stable 14

10 Chemical Bonds: Ionic Bonding (con.) Predominant bonding in Ceramics NaCl MgO 2.1 Li 1.0 Na 0.9 K 0.8 Rb 0.8 Cs 0.7 Fr 0.7 Be 1.5 Mg 1.2 Ca 1.0 Sr 1.0 Ba 0.9 Ra 0.9 Ti 1.5 Cr 1.6 Fe CaF2 CsCl Ni Zn As 2.0 O 3.5 F 4.0 Cl 3.0 Br 2.8 I 2.5 At 2.2 e Ne Ar Kr Xe Rn Give up electrons Acquire electrons 15

11 Chemical Bonds: Covalent Bonding Requires share electrons Directional bond Electronegativities are comparable Example: C 4 C has 4 valence eˉ, needs 4 more C4 shared electrons from carbon atom has 1 valence eˉ, needs 1 more C shared electrons from hydrogen atoms 16

12 Chemical Bonds: Covalent Bonding (con.) Molecule with nonmetals Molecule with metals and nonmetals Compound solids (about column IVA) 2.1 Li 1.0 Be O C(diamond) SiC column IVA C 2.5 O 2.0 F 4.0 e Ne F2 Cl2 Na 0.9 Mg 1.2 Si Cl 3.0 Ar K 0.8 Ca 1.0 Ti 1.5 Cr 1.6 Fe Ni Zn Ga 1.6 Ge As 2.0 Br 2.8 Kr Rb 0.8 Cs 0.7 Sr 1.0 Ba 0.9 Sn Pb I 2.5 At 2.2 Xe Rn Fr 0.7 Ra 0.9 GaAs 17

13 Chemical Bonds: Metallic Bonding Arises from a sea of donated valence electrons (1, 2, or 3 from each atom) Nondirectional bond Primary bond for metals and their alloys Ion cores Sea of valence electrons or electron cloud 18

14 Physical or van der Waals Bonds Arises from atomic or molecular dipoles. Weak in comparison to the primary bonds. 19

15 Physical Bonds: Fluctuating dipoles An electrically symmetric atom asymmetric electron clouds + + secondary bonding An induced atomic dipole ex: liquid secondary bonding Inert gases and electrically neutral and symmetric molecules, ex. 2, Cl 2 Weakest bonds 20

16 Physical Bonds: Polar Molecule Can induce dipoles in adjacent nonpolar molecules. Bond forms between the two molecules, which the magnitude is greater than for fluctuating induced dipoles. 21

17 Physical Bonds: Permanent dipoles Exist between adjacent polar molecules. Energy are greater than induced dipoles. Ex: ydrogen bonding: F, O, or N bond secondary bonding ydrogen Fluoride Polymer 22

18 Summary Type Ionic Covalent Metallic Secondary Bond Energy Large Variable large Diamond small Bismuth Variable large Tungsten small Mercury Smallest Comment Nondirectional (ceramics) Directional (semiconductor, ceramics, polymer chains) Nondirectional (metals) Directional (intermolecular, interchain polymer) 23