(Reference: Chang 9.2)Excellent! The valence number of the Group A elements come from their Group number.Perfect! 2. Explain the following: (3 points)a.Ionic bondIonic bonds are a type of electrostatic bond between two atoms that is weaker thancovalent bonds, but usually stronger than hydrogen. They are formed from themutual attraction of ions. Typical participants in an ionic bond are a metal and anon-metal, such as sodium and chlorine. Ionic bonds can be explained using the theory of electron orbitals. Every atom hasa number of electron orbitals equal to or greater than one. Each orbital has amaximum electron limit, after which a new orbital is created. The number oforbitals in the elements we know ranges from one for hydrogen or helium, to six,2Copyright © 2017 by Thomas Edison State University. All rights reserved.
seven, or eight for the larger molecules with atomic numbers greater thanuranium.Electron orbitals "want" to have the maximum number of electrons. That's whenthey're at their lowest, or most stable energy state. When an atom missing only asingle electron from its top orbital comes into contact with an atom that only hasone electron in its top orbital, the "wanting" atom "steals" an electron from theother atom, thereby stabilizing its orbital. The consequence is that it now has onemore electron than it has protons, making it negatively charged. The "victim" ofthe stolen electron correspondingly gains a positive charge. In electromagnetictheory, opposites attract, so the atoms are forced to hang around each other untilthey get broken up by, say, heat. That is what ionic bonds are.b.Nonpolar covalent bondA nonpolar bond is a covalent bond between atoms in which electrons are sharedequally between the atoms. The equal sharing of electrons results in the formationof a nonpolar molecule that has no electric dipole moment, or separation ofelectric charge. Two identical atoms will form a nonpolar bond because they haveequal electronegativities.A common example of a nonpolar bond can be found in diatomic oxygen. Eachoxygen atom has six electrons in its outer shell, needing two more to reach thestable eight-electron noble gas configuration. In the oxygen molecule, the atomsshare a set of four electrons equally in double bonds, satisfying each atom’s needfor an extra two electrons. Each of these bonds would be considered a nonpolarbond.Nonpolar covalent bonds tend to be found in diatomic molecules, where twoidentical atoms are bonded together. These include iodine, hydrogen, andnitrogen. The overall polarity of a molecule should not be confused with thepolarity of its bonds.c.Polar covalent bondA polar bond is a type of covalent chemical bond in which the electromagneticcharge of the molecule is split between both ends; i.e., one end of a molecule hasan overall positive charge and the other end has an overall negative charge. Thelinking of positive and negative charges in separate molecules allows them tobond with one another. The likelihood of atoms to form a polar bond depends on
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- Spring '08