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Covalent Bonds

Covalent Bonds. Terminology. Molecule – two or more atoms held together by covalent bonds Diatomic Molecule – molecule containing only 2 atoms Molecular Formula – shorthand notation for a covalently bonded substance showing the number and type of atoms example: C 6 H 12 O 6.

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Covalent Bonds

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  1. Covalent Bonds

  2. Terminology • Molecule – two or more atoms held together by covalent bonds • Diatomic Molecule – molecule containing only 2 atoms • Molecular Formula – shorthand notation for a covalently bonded substance showing the number and type of atoms example: C6H12O6

  3. Atoms held together by covalent bonds can only be separated by chemical reactions • Organic elements tend to form covalent bonds • Octet Rule – bonds tend to form so that an atom has an octet (8) of electrons in its last main energy level

  4. Forming the Bond • Orbitals overlap to form a bond • When 2 atoms approach the nucleus of one attracts the electron orbitals of the other • At the same time the nuclei of the two atoms repel • When the attraction outweighs the repulsion, the potential energy is lowest and the bond forms

  5. The non-bonding electrons repel as the atoms approach one another Force of attraction As the atoms get closer, the nuclei also start to repel

  6. Bond Length and Energy • Bond length is distance between two bonded atoms • Bond energy is energy needed to break the bond • In general, as bond length increases, the bond energy decreases (long bonds weaker)

  7. Bond Strength Bonded atoms Bond strength kJ/mol Bond length nm C-H 412 0.109 H-H 436 0.074 C-C 348 0.154 O-H 463 0.096 C-O 360 0.143 C-Cl 338 0.177 C-Br 276 0.193 C-I 238 0.214

  8. Multiple Bonds • Single Bond – share 1 pair of electrons • Double Bond – share 2 pair of electrons • Triple Bond – share 3 pair of electrons

  9. Only one pair of electrons holding the nuclei together Two pairs of electrons hold the nuclei tighter and closer

  10. Carbon bonds example Bonded atoms Bond strength kJ/mol Bond length nm C-C 348 0.154 C=C 612 0.134 C=C 837 0.120 As number of shared pairs of electrons increases the bond length decreases and bond energy increases

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