Covalent bonding Remember about ionic bonding…     A nonmetal (with a high IE and EA) will take an electron from a metal with a low IE and EA Electrons are TRANSFERRED from the cation to the anion Formulas are ratios of metals to nonmetals that form a crystalline structure NO IONIC MOLECULES!! Covalent bonding     Usually atoms that both have a higher IE and EA (nonmetals) They both want more electrons…but neither want to give them up! Electron pairs are shared between atoms Covalent bonds form molecular compounds or covalent molecules Comparison Ionic     Compounds form crystalline structures Electrons are transferred Bond between a metal and a nonmetal Ex: Covalent     Molecular compounds are formed Electrons are shared Bond between nonmetals Ex: Octet Rule     Atoms are most stable if they have 8 electrons in their valence shell Atoms share electrons in order to satisfy the octet rule A nonmetal will bond with as many atoms as it needs to satisfy the octet rule Double and triple bonding is a possibility for atoms to satisfy the octet rule Octet Rule Cont.  Think of the Lewis Dot of Carbon:  How many valence electrons does it have?  How many bonds will it form? Limits on the octet rule  H, He, Li     All strive for two electrons in their valence shell Li will transfer an electron H will share one electron in a covalent bond to be stable Be  Will sometimes form 2 covalent bonds Limits on the octet rule  B    Boron will form three covalent bonds and become stable The +5 charge of boron’s nucleus would not be strong enough to be stable with 8 v.e. “organometallic” compounds    Some metals will form covalent compounds with nonmetals (Hg, Sn, Ga, and others) The octet rule is only followed for the nonmetal Two or more covalent bonds are formed Limits on the octet rule  P, S, Cl, Se, Br, I   Atoms in the 3rd energy level or lower have an empty d orbital so there is room for more than 8 v.e. These elements at times will make more than 4 covalent bonds Diatomics  Diatomic molecules    A molecule made up of only two atoms Ex. CO Diatomic elements    A molecule made up of two atoms of the same element As pure elements, they form molecules with two atoms Heavenly-7 (H, N, O, F, Cl, Br, I)

Covalent Bonding

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