TYPES OF CHEMICAL BONDS

THREE TYPES OF BONDS Metallic bonds occur between metal atoms. This type of bond does not form compounds. Ionic bonds result from a transfer of electrons and will occur between a highly electronegative atom (nonmetal) and an atom of low electronegativity (metal). The oppositely charged ions formed from the transfer of electrons attract. 3. Covalent bonds result from sharing of electrons and will occur between two highly electronegative atoms (nonmetals).

Ionic bond ·· ·· Na · + · F  Na+ ·· ·· F ·· ·· ·· An ionic bond may result from electron transfer Atoms are held together by electrostatic attraction between positive and negative ions. ·· ·· – Na · + · F  Na+ ·· ·· F ·· ·· ··

IONIC COMPOUNDS Ionic bonding (strong) Properties high melting point, boiling point mostly water soluble solid is electrical insulator, liquid and solutions of ionic compounds are conductor Hard & brittle ex: NaCl

Covalent bond Shared electrons are in the outer energy level of both atoms The valence (outer) energy level of both of these H atoms now have 2 electrons. H H ··

POLAR COVALENT NONPOLAR COVALENT

partial positive charge partial negative charge Polar covalent bonds +  ·· H F – ·· ·· Less electronegative partial positive charge More electronegative partial negative charge

Covalent bond ·· ·· ·· ·· F · + · F  F ·· ·· ·· ·· F ·· ·· ·· ·· ·· Bonding electron pairs Nonbonding electron pairs, also called lone pairs ·· ·· ·· ·· F · + · F  F ·· ·· ·· ·· F ·· ·· ·· ·· ·· or ·· ·· F F ·· – ·· ·· ··

COVALENT COMPOUNDS Mostly lower melting points than ionic compounds Solid, liquid and aqueous solutions do not conduct electricity Some are soluble in water and some are not Do not break along planes

Trends in electronegativity Increases because Zeff increases, which attracts electrons more strongly. Outermost electrons are in same energy level (same n). Increases because valence electrons are closer to the nucleus (orbitals are smaller) so they are more strongly attracted to the atom.

Difference in Electronegativity Electronegativity Difference 0.00 0.65 0.94 1.19 1.43 1.67 1.91 2.19 2.54 3.03 Percent Ionic Character 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% Percent Covalent Character 100% Difference in Electronegativity 1.67 and greater 0 to .40 .40 to 1.67 NONPOLARCOVALENT POLAR COVALENT IONIC

Multiple bonds ·· ·· F F ·· – ·· ·· ·· ·· ·· O=O ·· ·· NN ·· ·· Atoms can share more than two electrons single bond F2 double bond O2 triple bond N2 ·· ·· F F ·· – ·· ·· ·· ·· ·· O=O ·· ·· NN ·· ··

Multiple bonds are fatter and stronger N2 O2 F2 triple bond double bond single bond

Metallic bond Metallic bonding can be pictured as positive metal ions in a sea of freely-moving negative electrons (delocalized electrons) Metallic bonding is moderate to strong Occurs between metal atoms.

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Metallic Solid Infinite array of atoms held together by metallic bonding Metallic bonding is like positive metal ions in a sea of freely-moving negative electrons Metallic bonding is moderate to strong Properties: moderate-to-high melting point, boiling point may be hard or soft electrically conductive solid and liquid malleable, ductile lustrous