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Unformatted text preview: ic charge and the H Example HF atom a slightly charge of equal magnitude. Aligns in an electric field. Aligns Polar molecules posses a Polar
12/04/09 Zumdahl Chapter 13 , μ.
9 Electronegativity (EN) vs. Electron Affinity (EA) • Electron affinity is a measure of the energy required to detach an electron from an atom or molecule: detach A− → A + e− , ∆ E ≡ EA EA (a large EA means a strong attraction of electrons) means • Electronegativity is a measure of the ability of an atom in a molecule to attract shared electrons to itself. in shared 12/04/09 Zumdahl Chapter 13 10 The Person Behind the Science Linus Pauling (1901-1994 )
Moments in a Life
1954 Nobel Prize in chemistry 1954 – Chemical Bonding, molecular biology • 1962 Nobel Peace Prize 1962 – Health (Vitamin C advocate) and Health Nuclear testing (banning atmospheric tests ) tests Electronegativity Scale: concept of partially ionic bonds. – fluorine with x = 4 is the most electronegative element, francium with x = fluorine 0.7 the least. Percent Ionic Character – x values can also be used to estimate the dipole moment and ionic character of bonds. character Pauling: Electronegativity is the power of an atom in a molecule to attract in electrons to itself. – x differs from the electron affinity of the free atom although the two run of roughly parallel. roughly 12/04/09 Zumdahl Chapter 13 11 • • • • The Pauling Electronegativity Values The as Updated by A.L. Allred in 1961 as Note: Note:
12/04/09 Zumdahl Chapter 13 12 Expected H−X bond energy =
1/2 [(H−H bond energy) (X−X bond energy)]1/2 [( (Geometric Mean of H−H and X−X Bond Energies) (Geometric Bond energy = expected bond energy if Bond expected Δ = EN(H) −EN(X) = 0. The larger Δ is, the stronger the H−X bond is. Ionic vs. Covalent Bonding
12/04/09 Zumdahl Chapter 13 13 Dipole moment: μ = Q r
1 debye(D)= 3.34*10^-30Cm Ionic Character = 100% if μ = Q r where where r = bond length (μ & r det’d experimentally) det’d bond Q = electron charge electron 12/04/09 Zumdahl Chapter 13 14 Non-Polar Covalent Non-Polar Bonding Bonding 12/04/09 Zumdahl Chapter 13 15 Ca: [Ar]4s2 Ca: [Ar]4s O: O:
12/04/09 Lose 2 electrons Ca2+: [Ar] or [Ne] [He] [He] 2s22p4Gain 2 electrons O2−: [He] 2s22p6 [He]
Zumdahl Chapter 13 16 Sizes of ions related to positions of elements in the periodic table.
Atomic Radii In In picometers picometers Cations: smaller Cations: than parent atom than Anions: larger than parent atom than Isoelectronic series: series: O2FNa+ Mg2+ 12/04/09 Zumdahl Chapter 13 Al3+ 17 Formation of Binary Ionic Compounds
Step 1: Vap. Of Li Step 2: Ion. Of Li Step 3: Dissoc. Of F2 Step 4: Electron Affinity for F Step 5: Lattice energy of LiF(s) Lattice Energy (5) can be calculated using a modified version of Coulomb’s Law (see text, p. 229) (see Li(s) + ½ F2(g) LiF(s) Li(s)
12/04/09 Zumdahl Chapter 13 18 Partial Ionic Character of Covalent Bonds Percent Ionic Character Covalent e.g., H2, Cl2 N2 Polar Covalent e.g., HF, H2O The relationship betwe...
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