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Chemical Bonding II: Covalent Bonds

Chemical Bonding II: Covalent Bonds. Review. Metals and nonmetals react to form ionic bonds. With ionic bonds, electrons are transferred. The resulting ions have noble-gas configurations. Ionic compounds are written as formula units: ex. NaCl. The Covalent Bond.

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Chemical Bonding II: Covalent Bonds

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  1. Chemical Bonding II:Covalent Bonds

  2. Review • Metals and nonmetals react to form ionic bonds. • With ionic bonds, electrons are transferred. • The resulting ions have noble-gas configurations. • Ionic compounds are written as formula units: ex. NaCl.

  3. The Covalent Bond • Atoms share electrons to achieve a stable octet. The bond that forms from shared electrons is a covalent bond. • Covalent bonding occurs when elements are fairly close to one another on the periodic table. Nonmetals form covalent bonds. This would be groups 14-17. • (video #1)

  4. Covalent bonds form molecules. Carbohydrates, simple sugars, proteins, fats, and DNA are covalently bonded molecules. • Diatoms are atoms that are sharing electrons to achieve a stable octet. They bond with themselves. There are seven diatomic molecules.

  5. Diatomic Molecules • Hydrogen: H2; shares one pair of electrons • Oxygen: O2; shares two pairs • Nitrogen: N2; shares three pairs • Iodine: I2; shares one pair • Bromine: Br2; shares one pair • Fluorine: F2; shares one pair • Chlorine: Cl2; shares one pair

  6. Unshared pairs of electrons are called lone pairs. • When a single pair of electrons is shared, a single covalent bond forms. Hydrogen and group 17 elements form SCBs.

  7. When two pairs are shared, a double covalent bond forms. Group 16 elements form DCBs. • When three pairs are shared, a triple covalent bond forms. Group 15 elements form TCBs.

  8. A triple bond has a shorter bond length than a double bond, and a double bond has a shorter length than a single bond. • The shorter the bond length, the stronger the bond. • Single bonds, therefore, are weaker than double bonds, and double bonds are weaker than triple bonds.

  9. Energy is released when a covalent bond forms, so energy must be added to break the bonds in a molecule. • The amount of energy required to break bonds is called bond dissociation energy, which is always positive.

  10. Endothermic reactions occur when energy is absorbed to break the bonds in the reactants. Exothermic reactions occur when energy is released and forms new bonds.

  11. Review • What is a covalent bond? How does it differ from an ionic bond? • What is a single covalent bond and how does it form? What family forms SCBs? • Why do multiple bonds form? What families form MCBs? • How is bond length related to bond disassociation energy?

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