Bond Character and Molecular Polarity How does atom electronegativity affect bond character and molecular polarity? Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Electronegativity The electronegativity value measures an atom’s tendency to attract electrons from other atoms is higher for nonmetals than for metals Why does this happen? What is going on in the atom with Coulombic attraction?

Some Electronegativity Values for Group A Elements Electronegativity decreases ` Electronegativity increases High values ` Low values

Nonpolar Covalent Bonds A nonpolar covalent bond occurs between nonmetals is an equal or almost equal sharing of electrons has almost no electronegativity difference (below 0.4) Examples: Electronegativity Atoms Difference Type of Bond N-N 3.0 - 3.0 = 0.0 Nonpolar covalent Cl-Br 3.0 - 2.8 = 0.2 Nonpolar covalent H-Si 2.1 - 1.8 = 0.3 Nonpolar covalent

Nonpolar Covalent Bond

Polar Covalent Bonds A polar covalent bond occurs between nonmetal atoms is an unequal sharing of electrons has a moderate electronegativity difference (0.4 to 1.7) Examples: Electronegativity Atoms Difference Type of Bond O-Cl 3.5 - 3.0 = 0.5 Polar covalent Cl-C 3.0 - 2.5 = 0.5 Polar covalent O-S 3.5 - 2.5 = 1.0 Polar covalent

Polar Covalent Bond

Comparing Nonpolar and Polar Covalent Bonds Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Ionic Bonds An ionic bond occurs between metal and nonmetal ions is a result of electron transfer has a large electronegativity difference (above 1.7) Examples: Electronegativity Atoms Difference Type of Bond Cl-K 3.0 – 0.8 = 2.2 Ionic N-Na 3.0 – 0.9 = 2.1 Ionic S-Cs 2.5 – 0.7 = 1.8 Ionic

Ionic Bond

Learning Check Use the electronegativity difference to identify the type of bond between the following: nonpolar covalent (NP), polar covalent (P), or ionic (I). A. K-N B. N-O C. Cl-Cl D. H-Cl < 0.4 Nonpolar covalent 0.4 to 1.7 Polar covalent > 1.7 Ionic Electronegativity Difference

Some Electronegativity Values for Group A Elements Electronegativity decreases ` Electronegativity increases High values ` Low values

Not all molecules with polar bonds are polar You will learn more about this when you study molecular geometry

Crosscutting Concepts Patterns in chemistry, and other sciences, we are always looking for patterns you were able to determine a pattern of nature of bonds formed when different atoms interact

Crosscutting Concepts Models in chemistry, and other sciences, we often use models to help us understand phenomenon you used a computer simulation to model the effect of changing electronegativity

Crosscutting Concepts Structure and Function in chemistry, and other sciences, the way an object is shaped or structured determines many of its properties and functions the structure of a molecule determines if it is polar or nonpolar

Nature of Science and Scientific Inquiry Laws vs Theories law-behavior of natural phenomenon or generalized relationships under certain conditions theory-well substantiated explanation of some aspect of natural world theories do not become laws even with additional evidence

Nature of Science and Scientific Inquiry Data vs Evidence data-measurements, observations, and findings collected as part of an investigation evidence-analyzed data and interpretation of the analysis