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Chapter 10 Structures of Solids and Liquids
10.3 Electronegativity and Polarity
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Electronegativity Electronegativity
is the relative ability of atoms to attract shared electrons is higher for nonmetals, with fluorine as the highest with a value of 4.0 is lower for metals, with cesium and francium as the lowest with a value of 0.7 increases from left to right going across a period on the periodic table decreases going down a group on the periodic table
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Some Electronegativity Values for Group A Elements
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Learning Check Using the periodic table, predict the order of increasing electronegativity for the elements O, K, and C.
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Solution The metal K on the left of Period 4 has the lowest electronegativity of the three elements. The nonmetal O on the upper right of Period 2 has the highest electronegativity. The nonmetal C, which is on the left of O in the periodic table, has a lower electronegativity than O, but a higher electronegativity than K. Order of increasing electronegativity: K, C, O
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Nonpolar Covalent Bonds
A nonpolar covalent bond occurs between nonmetal atoms consists of an equal (or almost equal) sharing of electrons has a zero (or close to zero) electronegativity difference of 0.0 to 0.4 Examples: Atoms Electronegativity Type of Bond Difference NN = Nonpolar covalent ClBr = Nonpolar covalent HSi = Nonpolar covalent
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Polar Covalent Bonds A polar covalent bond
occurs between nonmetal atoms consists of atoms that share electrons unequally has an electronegativity difference range of 0.5 to 1.7 Examples: Atoms Electronegativity Type of Bond Difference OCl = 0.5 Polar covalent ClC = 0.5 Polar covalent OS = 1.0 Polar covalent
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Comparing Nonpolar and Polar Covalent Bonds
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Ionic Bonds An ionic bond occurs between metal and nonmetal ions
is a result of electron transfer has a large electronegativity difference (1.8 or more) Examples: Atoms Electronegativity Type of Bond Difference ClK – 0.8 = Ionic NNa 3.0 – = Ionic SCs 2.5 – 0.7 = Ionic
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Electronegativity and Bond Types
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Predicting Bond Types
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Learning Check Use electronegativity differences to classify each of the following bonds as nonpolar covalent (NP), polar covalent (P), or ionic (I): A bond between A. K and N B. N and O C. Cl and Cl D. H and Cl
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Solution Atoms in Electronegativity Type of Bond Difference Bond
A. K and N ionic (I) B. N and O polar covalent (P) C. Cl and Cl nonpolar covalent (NP) D. H and Cl polar covalent (P)
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Polar Molecules A polar molecule contains polar bonds
has a separation of positive and negative charge called a dipole indicated by a dipole arrow has dipoles that do not cancel
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Nonpolar Molecules A nonpolar molecule
may contain identical atoms (nonpolar bonds) may have a symmetrical arrangement of polar bonds that cancel dipoles
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Determining Molecular Polarity
The polarity of a molecule is determined from its electron-dot formula shape polarity of the bonds dipole cancellation
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Learning Check Identify each of the following molecules as
(P) polar or (NP) nonpolar: A. PBr3 B. HBr C. Br2 D. SiBr4
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Solution Identify each of the following molecules as
(P) polar or (NP) nonpolar: A. PBr (P) pyramidal; dipoles don’t cancel; polar B. HBr (P) linear; one polar bond (dipole); polar C. Br (NP) linear; nonpolar bond; nonpolar D. SiBr4 (NP) tetrahedral; dipoles cancel; nonpolar
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