Chapter 5 Compounds and Their Bonds

Chapter 5Compounds and Their Bonds 5.1Octet Rule and Ions

Octet Rule An octet • is 8 valence electrons • is associated with the stability of the noble gases • does not occur with He; He is stable with 2 valence electrons (duet) Valence Electrons He 1s22 Ne 1s22s22p68 Ar 1s22s22p63s23p6 8 Kr 1s22s22p63s23p64s23d104p6 8

Ionic and Covalent Bonds Atoms form octets • to become more stable • bylosing, gaining, orsharingvalence electrons • by forming ionicor covalent bonds

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 1A(1) metals ion 1+ Group 2A(2) metals ion 2+ Group 3A(3) metals ion 3+

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

Charge of Sodium Ion, Na+ With the loss of its valence electron, a sodium ion has a 1+ charge. Sodium atom Sodium ion 11p+ 11p+ 11e–10e– 0 1 +

Formation of Magnesium Ion, Mg2+ Magnesium achieves an octet by losing its two valence electrons.

Charge of Magnesium Ion, Mg2+ With the loss of two valence electrons magnesium forms a positive ion with a 2+ charge. Mg atom Mg2+ ion 12p+ 12p+ 12e–10e– 0 2+

Learning Check A. The number of valence electrons in aluminum is 1) 1e– 2) 2e– 3) 3e– B. To acquire an octet of electrons in aluminum requires 1) a loss of 3e– 2) a gain of 3e– 3) a gain of 5e– C. The ionic charge of aluminum is 1) 3– 2) 5– 3) 3+ D. The symbol for the aluminum ion is 1) Al3+ 2) Al3– 3) Al+

Solution A. The number of valence electrons in aluminum is 3) 3 e– B. To acquire an octet of electrons in aluminum requires 1) a loss of 3e– C. The ionic charge of aluminum is 3) 3+ D. The symbol for the aluminum ion is 1) Al3+

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

Formation of a Chloride Ion, Cl– Chlorine achieves an octet by adding an electron to its valence electrons.

Charge of a Chloride Ion, Cl– • By gaining one electron, the chloride ion has a –1 charge. Chlorine atom Chloride ion 17p+ 17p+ 17e–18e– 0 1–

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

Some Typical Ionic Charges

Group Number and Ionic Charge Ions • achieve the electron configuration of their nearest noble gas • of metals in Groups 1A(1), 2A(2), or 3A(13) have positive 1+, 2+, or 3+ charge. • Of nonmetals in Groups 5A(15), 6A(16), or 7A(17) have negative 3–, 2–, or 1– charge.

Groups Numbers for Some Positive and Negative Ions

Learning Check A. The Group number for sulfur is 1) 4A(14) 2) 8A(18) 3) 6A(16) B. The number of valence electrons in sulfur is 1) 4e 2) 6e 3) 8e C. The change in electrons for an octet requires a 1) gain of 2e2) loss of 2e3) a gain of 4e D. The ionic charge of sulfur is 1) 2+ 2) 2 3) 4

Solution A. The Group number for sulfur is 3) 6A(16) B. The number of valence electrons in sulfur is 2) 6e C. The change in electrons for octet requires a 1) gain of 2e D. The ionic charge of sulfur is 2) 2

Sizes of Atoms and Their Ions Metals • lose their valence electrons • form ions that are smaller than their atoms Nonmetals (in ionic compounds) • gain valence electrons • form ions that are larger than their atoms

Metal Ions are Smaller In Group 1A(1), the ions are smaller than their corresponding atoms.

Nonmetal Ions are Larger In Group 7A(17), the ions are larger than their corresponding atoms.

Learning Check Select the larger atom or ion in the following: 1. Mg or Mg2+ 2. S or S2 3. Br or Br

Solution Select the larger atom or ion in the following: 1. Mg or Mg2+ Mg 2. S or S2 S2 3. Br or Br Br

Chapter 5 Compounds and Their Bonds