Electronegativity and Polarity PDF

Essential Questions How is electronegativity used to determine bond type? How do polar and nonpolar covalent bonds and polar and nonpolar molecules compare and contrast? What are the characteristics of covalently bonded compounds? Copyright © McGraw-Hill Education Electronegat...

Essential Questions How is electronegativity used to determine bond type? How do polar and nonpolar covalent bonds and polar and nonpolar molecules compare and contrast? What are the characteristics of covalently bonded compounds? Copyright © McGraw-Hill Education Electronegativity and Polarity Vocabulary Review New electronegativity polar covalent bond Copyright © McGraw-Hill Education Electronegativity and Polarity Electronegativity and Bond Character Electron affinity measures the tendency of an atom to accept an electron. Noble gases are not listed because they generally do not form compounds. Copyright © McGraw-Hill Education Electronegativity and Polarity Electronegativity and Bond Character This table lists the character and type of chemical bond that forms with differences in electronegativity. Copyright © McGraw-Hill Education Electronegativity and Polarity Electronegativity and Bond Character Unequal sharing of electrons results in a polar covalent bond. Bonding is often not clearly ionic or covalent. This graph summarizes the range of chemical bonds between two atoms. Copyright © McGraw-Hill Education Electronegativity and Polarity Polar Covalent Bonds Polar covalent bonds form when atoms pull on electrons in a molecule unequally. Electrons spend more time around one atom than another resulting in partial charges at the ends of the bond called a dipole. Copyright © McGraw-Hill Education Electronegativity and Polarity Polar Covalent Bonds Covalently bonded molecules are either polar or non-polar. Non-polar molecules are not attracted by an electric field. Polar molecules align with an electric field. Compare water, H2O, and CCl4. – Both bonds are polar. – The molecular shapes, determined by VSEPR, is bent and tetrahedral, respectively. – O – H bonds are asymmetric in water, so has a definite positive end and definite negative end. Thus, polar. The C – Cl bonds are symmetrical in CCl4. The electric charge measured at any distance from the center is identical on all sides and partial charges are balanced. Thus nonpolar. Copyright © McGraw-Hill Education Electronegativity and Polarity Polar Covalent Bonds Note: If bonds are polar, asymmetrical molecules are polar and symmetrical molecules are nonpolar. Copyright © McGraw-Hill Education Electronegativity and Polarity Polar Covalent Bonds Solubility is the property of a substance’s ability to dissolve in another substance. Polar molecules and ionic substances are usually soluble in polar substances. Non-polar molecules dissolve only in non-polar substances. Copyright © McGraw-Hill Education Electronegativity and Polarity Properties of Covalent Compounds Covalent bonds between atoms are strong, but attraction forces between molecules are weak. The weak attraction forces are known as van der Waals forces. The forces vary in strength but are weaker than the bonds in a molecule or ions in an ionic compound. Non-polar molecules exhibit a weak dispersion force, or induced dipole. The force between two oppositely charged ends of two polar molecules is a dipole-dipole force. A hydrogen bond is an especially strong dipole-dipole force between a hydrogen end of one dipole and a fluorine, oxygen, or nitrogen atom on another dipole. Copyright © McGraw-Hill Education Electronegativity and Polarity Properties of Covalent Compounds Many physical properties are due to intermolecular forces. Weak forces result in the relatively low melting and boiling points of molecular substances. Many covalent molecules are relatively soft solids. Molecules can align in a crystal lattice, similar to ionic solids but with less attraction between particles. Solids composed of only atoms interconnected by a network of covalent bonds are called covalent network solids. Quartz and diamonds are two common examples of network solids. Copyright © McGraw-Hill Education Electronegativity and Polarity Review Essential Questions How is electronegativity used to determine bond type? How do polar and nonpolar covalent bonds and polar and nonpolar molecules compare and contrast? What are the characteristics of covalently bonded compounds? Vocabulary polar covalent bond Copyright © McGraw-Hill Education Electronegativity and Polarity