Frederick A. Bettelheim William H. Brown Mary K. Campbell Shawn O. Farrell William H. Brown, Beloit College Chapter 3 CHEMICAL BONDS
3-2 Lewis Model of Bonding • In 1916, Gilbert N. Lewis pointed out that the lack of chemical reactivity of the noble gases indicates a high degree of stability of their electron configurations. He 1s 2 Ne Ar Kr Xe [He]2s 2 2p 6 [Ne]3s 2 3p 6 [Ar]4s 2 4p 6 [Kr]5s 2 5p 6 Noble gas Noble gas notation
3-3 The Octet Rule • Octet rule: Octet rule: The tendency of group 1A-7A elements to react in ways that achieve an electron configuration of eight valence electrons. • An atom that loses one or more electrons becomes a positively charged ion called an cation. cation. • An atom that gains one or more electrons becomes a negatively charged ion called a anion. anion.
3-4 The Octet Rule • Example: In losing one electron, a sodium atom forms a sodium ion, which has the same electron configuration as neon. Na (11 electrons): 1s 2 2s 2 2p 6 3s 1 Na + (10 electrons): 1s 2 2s 2 2p 6
3-5 The Octet Rule • Example: In gaining one electron, a chlorine atom forms a chloride ion, which has the same electron configuration as argon. Chlorine atom (17 electrons): 1s 2 2s 2 2p 6 3s 2 3p 5 Chloride ion (18 electrons): 1s 2 2s 2 2p 6 3s 2 3p 6
3-6 The Octet Rule • The octet rule gives us a good way to understand why Group 1A-7A elements form the ions they do; but it is not perfect: • Ions of Period 1 and 2 elements with charges greater than +2 are unstable. For example, boron does not lose its three valence electrons to become B 3+ , nor does carbon lose its four valence electrons to become C 4+ . • Ions of Period 1 and 2 elements with charges greater than -2 are also unstable. For example, carbon does not gain four valence electrons to become C 4- . • The octet rule does not apply to Group 1B-7B (transition elements), most of which form ions with two or more different positive charges.
3-7 Naming Cations • Elements of Groups 1A, 2A, and 3A form only one type of cation. • The name of the cation is the name of the metal followed by the word “ion”. Li + H + Hydrogen ion Lithium ion Sodium ion Potassium ion Ion K + Na + Mg 2+ Magnesium ion Calcium ion Strontium ion Barium ion Ca 2+ Sr 2+ Ba 2+ Al 3+ Aluminum ion Name Ion Name Ion Name Group 1A Group 2A Group 3A
3-8 Naming Cations • For cations derived from transition and inner transition elements, most of which form more than one type of cation: • Use either Roman numerals to show charge or • Use the suffix -ous -ous to show the lower positive charge and the suffix -ic -ic to show the higher positive charge.
3-9 Naming Cations • Table 3.2 Names of Cations from Four Metals That Form Two Different Positive Ions Fe 3+ Fe 2+ Hg + Hg 2+ Cu 2+ Cu + Copper(I) ion Copper(II) ion Iron(II) ion Iron(III) ion Mercury(I) ion Mercury(II) ion Cuprous ion Cupric ion Ferrous ion Ferric ion Mercurous ion Mercuric ion Cupr- from cuprum , the Latin name for copper Hg from hydrargyrum , the