Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings Valence Electrons 4.2 Octet Rule and Ions Chapter 4 Compounds and Their Bonds

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 2  The valence electrons are the electrons in the outer shell.  The electrons in the outer shell have the most contact with other atoms and strongly influence the chemical properties of atoms. Valence Electrons

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 3 Number of Valence Electrons For Group A elements, the number of valence electrons is the number of electrons in the s and p subshells of the outer shell. In the electron configuration for phosphorus, there are 5 valence electrons in the s and p subshells with the highest number. 5 valence electrons P Group 5A 1s 2 2s 2 2p 6 3s 2 3p 3

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 4 Valence Electrons for Groups

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 5 Electron Dot Structure An electron-dot structure is a convenient way to represent the valence electrons. For example, the two valence electrons for magnesium are placed as single dots on any two sides of the Mg symbol.

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 6 Electron-Dot Structures Dot structures are used for Group A elements. The valence electrons are placed on the sides of the symbol of an element.

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 7  The stability of the noble gases is associated with 8 valence electrons (He has 2). Ne 2, 8 Ar2, 8, 8 Kr2, 8, 18, 8  Atoms can become more stable by acquiring an octet (8 electrons) in the outer shell.  The process of acquiring an octet involves the loss, gain, or sharing of valence electrons.  Main Group Elements!! Octet Rule

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 8 Ionization Energy Ionization energy is the energy it takes to remove a valence electron. Metals have lower ionization energies and nonmetals have higher ionization energies.

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 9  Metals acquire octets by losing valence electrons.  The loss of electrons converts an atom to an ion that has the electron configuration of the nearest noble gas.  Metals form positive ions because they have fewer electrons than protons. Group 1A metals  ion 1+ Group 2A metals  ion 2+ Group 3A metals  ion 3+ Metals Form Positive Ions

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 10 Sodium forms an octet by losing its one valence electron. Na  – e   Na + 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 (= Ne) A positive ion forms with a +1 charge. Sodium atom Sodium ion 11 p + 11 e - 10 e Formation of a Sodium Ion, Na +

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 11 Magnesium forms an octet by losing its two valence electrons. Magnesium atom Magnesium ion  Mg  – 2e   Mg 2+ 1s 2 2s 2 2p 6 3s 2 1s 2 2s 2 2p 6 (= Ne) A positive ion forms with a +2 charge. 12 p + 12 p + 12 e- 10 e Formation of Mg 2+

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 12  Nonmetals gain electrons to achieve an octet arrangement, they form negative ions.  The ionic charge of a nonmetal is 3-, 2-, or 1-. Formation of Negative Ions

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 13 Fluorine forms an octet by adding an electron to its seven valence electrons.     1 - : F  + e  : F :     1s 2 2s 2 2p 5 1s 2 2s 2 2p 6 (= Ne) A negative ion forms with a -1 charge. Fluorine atom Fluoride ion 9 p + 9 p + 9 e - 10 e – Formation of a Fluoride Ion, F -

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 14 Group Number and Ions The Group number can be used to determine the charge of an ion. The charge of a positive ion is equal to its Group number. Group 3A = 3+ The charge of a negative ion is obtained by subtracting its Group number from 8. Group 6A = - (8-6) = 2-

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 15 Examples of Ionic Charges

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 16 Some Important Ions in the Body

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 17 Chapter 4 Compounds and Their Bonds 4.3 Ionic Compounds 4.4 Naming and Writing Ionic Formulas

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 18  Ionic compounds consist of positive and negative ions.  An ionic bond is an attraction between the positive and negative charges.  In an ionic formula, the total charge of the positive ions is equal to the total charge of the negative ions. total positive charge = total negative charge Ionic Compounds

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 19 The formulas of ionic compounds are determined from the charges on the ions. atoms ions     – Na  +  F :  Na + : F :  NaF     sodium fluorine sodium fluoride The overall charge of NaF is zero (0). (1+ ) + (1-) = 0 Ionic Formulas

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 20 Charge Balance In NaCl The formula does not show the charges of the ions in the compound. The symbol of the metal is written first, followed by the symbol of the nonmetal.

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 21 Charge Balance In MgCl 2

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 22 Write the formula of the ionic compound that forms from Ba 2+ and Cl . Write the symbols of the positive ion and the negative ion. Ba 2+ Cl  Balance the charges until the positive charge is equal to the negative charge. Ba 2+ Cl  two Cl - needed Cl  Write the formula using subscripts for the number of ions for charge balance. BaCl 2 Writing a Formula from Charges

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 23 Names of Ions Positive ions are named like the element. Negative ions are named by changing the end of the element name to –ide.

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 24 The name of a binary ionic compound (two elements) gives the name of the metal ion first and the name of the negative ion second. Examples: NaClsodium chloride K 2 Spotassium sulfide CaI 2 calcium iodide Al 2 O 3 aluminum oxide Naming Ionic Compounds with Two Elements

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 25  Most transition elements have two or more positive ions. Ionic Charges of Transition Metals

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 26 Summary of Common Ions Of the transition metals, silver and zinc are important elements that form only one ion.

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 27 Naming Compounds with Transition Metals Transition metals with two different ions use a Roman numeral following the name of the metal to indicate ionic charge.

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings Covalent Bonds 4.6 Naming and Writing Formulas of Covalent Compounds 4.7 Bond Polarity Chapter 4 Compounds and Their Bonds

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 29  Covalent bonds form between two nonmetals from Groups 4A, 5A, 6A, and 7A.  In a covalent bond, electrons are shared to complete octets. Covalent Bonds

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 30 In hydrogen, two hydrogen atoms share their electrons to form a covalent bond. Each hydrogen atom acquires a stable outer shell of two (2) electrons like helium (He). H  +  H H : H = H  H = H 2 hydrogen molecule H 2, A Covalent Molecule

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 31 Diatomic Elements As elements, the following share electrons to form diatomic, covalent molecules.

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 32 The compound NH 3 consists of a N atom and three H atoms.    N  and 3 H   By sharing electrons to form NH 3, the electron dot structure is written as H Bonding pairs   H : N : H   Lone pair of electrons Covalent Bonds in NH 3

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 33 Number of Covalent Bonds Often, the number of covalent bonds formed by a nonmetal is equal to the number of electrons needed to complete the octet.

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 34 Dot Structures and Models of Some Covalent Compounds

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 35 Multiple Bonds  Sharing one pair of electrons is a single bond. X : X or X–X  In multiple bonds, two pairs of electrons are shared to form a double bond or three pairs of electrons are shared in a triple bond. X : : X or X =X X : : : X or X ≡ X

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 36 In nitrogen, octets are achieved by sharing three pairs of electrons. When three pairs of electrons are shared, the multiple bond is called a triple bond. octets          N  +  N   N:::N  triple bond Multiple Bonds in N 2

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 37 In the name of a covalent compound, the first nonmetal is named followed by the name of the second nonmetal ending in –ide.  Prefixes indicate the number of atoms of each element. Naming Covalent Compounds

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 38 Formulas and Names of Some Covalent Compounds

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 39  Electronegativity is the attraction of an atom for shared electrons.  The nonmetals have high electronegativity values with fluorine as the highest.  The metals have low electronegativity values. Electronegativity

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 40 Some Electronegativity Values for Group A Elements

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 41  The atoms in a nonpolar covalent bond have electronegativity differences of 0.3 or less.  Examples: Atoms Electronegativity Type of Difference Bond N-N = 0.0 Nonpolar covalent Cl-Br = 0.2 Nonpolar covalent H-Si = 0.3 Nonpolar covalent Nonpolar Covalent Bonds

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 42  The atoms in a polar covalent bond have electronegativity differences of 0.4 to 1.6.  Examples: Atoms Electronegativity Type of Difference Bond O-Cl = 0.5 Polar covalent Cl-C = 0.5 Polar covalent O-S = 1.0 Polar covalent Polar Covalent Bonds

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 43 Comparing Nonpolar and Polar Covalent Bonds

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 44 Ionic Bonds  The atoms in an ionic bond have electronegativity differences of 1.7 or more.  Examples: Atoms ElectronegativityType of Difference Bond Cl-K 3.0 – 0.8 = 2.2Ionic N-Na 3.0 – 0.9 = 2.1Ionic S-Cs2.5 – 0.7= 1.8Ionic

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 45 Range of Bond Types

Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings. 46 Predicting Bond Type