Chapter 4 Compounds and Their Bonds 4 1

Learning Goals l Using the octet rule, write the symbols of the simple ions for the representative elements. l Using charge balance, write the correct formula for an ionic compound. l Given the formula of an ionic compound, write the correct name; given the name of an ionic compound, write the correct formula. l Write the name and formula of a compound containing a polyatomic ion. l Given the formula of a covalent compound, write its correct name; given the name of a covalent compound, write its formula. l Use electronegativity to determine the polarity of a bond. l Predict the three-dimensional structure of a molecule and classify it as polar or nonpolar. 2

Octet Rule An octet • is 8 valence electrons. • is associated with the stability of the noble gases. He is stable with 2 valence electrons (duet). He Ne Ar Kr 2 2, 8, 8 2, 8, 14, 8 valence electrons 2 8 8 8 3

Ionic and Covalent Bonds Atoms form octets • to become more stable. • by losing, gaining, or sharing valence electrons. • by forming ionic bonds or covalent bonds. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 4

Metals Form Positive Ions Metals form positive ions • by a loss of their valence electrons. • with the electron configuration of the nearest noble gas. • that have fewer electrons than protons. Group 1 A metals ion 1+ Group 2 A metals ion 2+ Group 3 A metals ion 3+ Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 5

Formation of a Sodium Ion, Na+ Sodium achieves an octet by losing its one

Charge of Sodium Ion, Na+ With the loss of its valence electron, the sodium ion has a +1 charge. Sodium atom 11 p+ 11 e 0 Sodium ion 11 p+ 10 e 1+ 2, 8 Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 7

Formation of Mg 2+ Magnesium achieves an octet by losing its two valence electrons.

Charge of Magnesium Ion Mg 2+ With the loss of two valence Electrons, magnesium forms a positive ion with a +2 charge. Mg atom 12 p+ 12 e 0 Mg 2+ ion 12 p+ 10 e 2+ Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 9

Learning Check A. The number of valence electrons in aluminum is 1) 1 e-. 2) 2 e-. 3) 3 e-. B. The change in electrons for octet requires a 1) loss of 3 e-. 2) gain of 3 e-. 3) a gain of 5 e-. C. The ionic charge of aluminum is 1) 3 -. 2) 5 -. 3) 3+. D. The symbol for the aluminum ion is 1) Al 3+. 2) Al 3 -. 3) Al+. 10

Solution A. The number of valence electrons in aluminum is 3) 3 e-. B. The change in electrons for octet requires a 1) loss of 3 e-. C. The ionic charge of aluminum is 3) 3+. D. The symbol for the aluminum ion is 1) Al 3+. 11

Formation of Negative Ions In ionic compounds, nonmetals • achieve an octet arrangement. • gain electrons. • form negatively charged ions with 3 -, 2 -, or 1 charges. 12

Formation of a Chloride, Cl. Chlorine achieves an octet by adding an electron to

Charge of a Chloride Ion, Cl. By gaining one electron, the chloride ion has a -1 charge. Chlorine atom 17 p+ 17 e 0 Chloride ion 17 p+ 18 e 1– Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 14

Ionic Charge from Group Numbers • The charge of a positive ion is equal to its Group number. Group 1 A(1) = 1+ Group 2 A(2) = 2+ Group 3 A(3) = 3+ • The charge of a negative ion is obtained by subtracting 8 or 18 from its Group number. Group 6 A(16) = 6 - 8 = 2 or 16 - 18 = 2 - 15

Some Ionic Charges ICopyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Learning Check A. The number of valence electrons in sulfur is 1) 4 e-. 2) 6 e-. 3) 8 e-. B. The change in electrons for octet requires a 1) loss of 2 e-. 2) gain of 2 e-. 3) a gain of 4 e-. C. The ionic charge of sulfur is 1) 2+. 2) 2 -. 3) 4 -. 17

Solution A. The number of valence electrons in sulfur is 2) 6 e-. B. The change in electrons for octet requires a 2) gain of 2 e-. C. The ionic charge of sulfur is 2) 2 -. 18