Inorganic chemistry Assistance Lecturer Amjad Amjad Jumaa  Chemical bonds.  Ionic Bonds,  Covalent Bonds. 1

 Chemical bonds: Is defined as a force that acts between two or more atoms to hold them together as a stable molecule.  Ionic Bonds: Electrostatic attraction between a positive ion (cation), and negative ion (anion),(oppositely charged ions). For example: formation of LiF:  Chemical bonds: Is defined as a force that acts between two or more atoms to hold them together as a stable molecule.  Ionic Bonds: Electrostatic attraction between a positive ion (cation), and negative ion (anion),(oppositely charged ions). For example: formation of LiF:

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 Covalent Bonds The attractive force between atoms created by sharing of an electron pair to form a stable compound called covalent compounds. For example: formation of H 2 molecule:  Covalent Bonds The attractive force between atoms created by sharing of an electron pair to form a stable compound called covalent compounds. For example: formation of H 2 molecule:

Formation of ammonia (NH 3 ) molecule: Formation of HCl molecule:

6  The covalent, or shared electron pair, model of chemical bonding was first suggested by G. N. Lewis of the University of California in Lewis proposed that a sharing of two electrons by two hydrogen atoms permits each one to have a stable closed-shell electron configuration analogous to helium.

7  The Lewis model limits second-row elements (Li, Be, B, C, N, O, F, Ne) to a total of 8 electrons (shared plus unshared) in their valence shells. Hydrogen is limited to 2. Most of the elements that we’ll encounter in this text obey the octet rule: in forming compounds they gain, lose, or share electrons to give a stable electron configuration characterized by eight valence electrons. When the octet rule is satisfied for carbon nitrogen, oxygen, and fluorine, they have an electron configuration analogous to the noble gas neon. Now let’s apply the Lewis model to the organic compounds methane and carbon tetrafluoride.

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9  Carbon has 8 electrons in its valence shell in both methane and carbon tetrafluoride. By forming covalent bonds to four other atoms, carbon achieves a stable electron configuration analogous to neon. Each covalent bond in methane and carbon tetrafluoride is quite strong—comparable to the bond between hydrogens in H2 in bond dissociation energy.  Lewis’s concept of shared electron pair bonds allows for 4-electron double bonds and 6-electron triple bonds. Carbon dioxide (CO 2 ) has two carbon– oxygen double bonds, and the octet rule is satisfied for both carbon and oxygen. Similarly, the most stable Lewis structure for hydrogen cyanide (HCN) has a carbon–nitrogen triple bond.

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