52_100_Lecture_3

52_100_Lecture_3 - 9/3/2007 Polar Vs. Nonpolar Bonds...

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9/3/2007 1 Polar Vs. Nonpolar Bonds Electronegativity: the measure of the ability of an atom to attract electrons in a covalent bond toward itself. 1 Polar Vs. Nonpolar Bonds If there is a difference between the electronegativity of the two atoms bound together, then the bond is polar. HF Flourine is more electronegative than hydrogen This is a polar bond The shift in the electrons toward the fluorine creates a dipole. The dipole points toward the more electronegative atom. δ + δ 2 There is a partial negative charge on the atom that the dipole points toward and a partial positive charge on the atom the dipole points away from.
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9/3/2007 2 Polar Vs. Nonpolar Bonds If the two atoms bound together are the same atom then the bond is a nonpolar bond. Cl Cl There is no electronegativity difference between two atoms of the same element. CH The difference between carbon and hydrogen is so small that C-H bonds are considered nonpolar. 3 Electrolytes and Nonelectrolytes Electrolyte: substances that conduct electricity when dissolved in water or when melted Sodium chloride was an electrolyte Nonelectrolyte: substances that do not conduct electricity when dissolved in water or when melted Sugar was a nonelectrolyte 4 What is the major difference between sugar and salt?
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9/3/2007 3 It is the presence of the ions in the water that allows electricity to be conducted in a salt water solution Electrolytes and Nonelectrolytes Water itself is a very weak electrolyte because it is a molecular compound that can ionize Ionization: the conversion of molecular compounds into ions HO H H + + OH - 5 Hydrogen halides (HF, HCl, HBr, & HI) also ionize quite readily Equilibrium arrow Electrolytes and Nonelectrolytes Chemical Equations Salt and Water Sugar and Water NaCl (s) + H 2 O (l) Na + (aq) + Cl - (aq) C 6 H 12 O 6 (s) + H 2 O (l) C 6 H 12 O 6 (aq) 6 Aq = aqueous – a solution with water as the main component
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9/3/2007 4 Wait! If sugar is not ionic then why does it Wait! If sugar is not ionic, then why does it dissolve in water? 7 Bond Polarity and Molecular Polarity If a molecule has bonds that are polar, it can make the entire molecule polar The geometry of the molecule must be identified in order to The geometry of the molecule must be identified in order to determine the polarity of the molecule Linear : 2 atoms with 180 o angles around the central atom Trigonal planar: 3 atoms with 120 o angles around the central atom 8 Tetrahedral :
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52_100_Lecture_3 - 9/3/2007 Polar Vs. Nonpolar Bonds...

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