che106_Lecture18

che106_Lecture18 - Chemistry 106 Lecture 18 Topics: Ionic...

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Chemistry 106 Lecture 18 Topics: Ionic and Covalent Bonds Polarity Chapter 8.1-8.4
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Types of Chemical Bonds Three basic types of bonds Ionic Electrostatic attraction between ions Magnesium Oxide (MgO) Covalent Sharing of electrons Benzene (C6H6) Metallic Metal atoms bonded to other metal atoms
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Ionic Compounds: Sodium Chloride
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Describing Ionic Bonds An ionic bond is a chemical bond formed by the electrostatic attraction between positive and negative ions ( Coulomb’s Law ). This type of bond involves the transfer of electrons from one atom (usually a metal) to another (usually a nonmetal). The number of electrons lost or gained by an atom is determined by its need to be isoelectronic ” with a noble gas. Isoelectronic = “same electron configuration as”
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Metal Non-metal +1 -1 Ionic Compounds: Sodium Chloride
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Describing Ionic Bonds Such noble gas configurations and the corresponding ions are very stable. Therefore, atoms tend toward noble gas character. (often 8 valence e- or an “octet”) The atom that loses the electron becomes a cation (positive). The atom that gains the electron becomes an anion (negative). [Ar] - 1 e ]) Ne ([ Na ) s 3 ] Ne ([ Na + + ) p 3 s 3 ] Ne ([ Cl e ) p 3 s 3 ] Ne ([ Cl 6 2 - 5 2 - +
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Describing Ionic Bonds Consider the transfer of valence electrons from a sodium atom to a chlorine atom. The resulting ions are electrostatically attracted to one another. The attraction of these oppositely charged ions for one another is the ionic bond. e - - + + + Cl Na Cl Na
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Lewis Electron-Dot Symbols A Lewis electron-dot symbol is a symbol in which the electrons in the valence shell of an atom or ion are represented by dots placed around the letter symbol of the element. Ø Note that the group number indicates the number of valence electrons . Na . . . . . Si . . . : P : . . S Mg . . . Al . . : Cl . Ar : : Group 1A Group 2A Group 7A Group 8A Group 6A Group 4A Group 5A Group 3A
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Lewis Electron-Dot Symbols
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Lewis Electron-Dot Formulas A Lewis electron-dot formula is an illustration used to represent the transfer of electrons during the formation of an ionic bond. As an example, let’s look at the transfer of electrons from magnesium to fluorine to form magnesium fluoride (MgF2).
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[Ne]3s2 [He]2s22p5 Lewis Electron-Dot Formulas
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Lewis Electron-Dot Formulas Consequently, magnesium can accommodate two fluorine atoms. : : F . : F . Mg . . Mg [ F ] : : 1- 2+ [ F ] : : 1- The magnesium atom has two electrons to give, whereas the fluorine atoms have only one “vacancy” each.
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Energy Involved in Ionic Bonding If atoms come together and bond, there needs to be a net decrease in energy . The bonded state must be more stable
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che106_Lecture18 - Chemistry 106 Lecture 18 Topics: Ionic...

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