SO2, XeF2, ClF3, SF4, XeF4, BrF5, PCl5, SF6 Exceptions to the octet rule fall into one of three categories: (1) incomplete octet, (2) odd-electron molecules, and (3) an expanded octet. Incomplete Octet: In some compounds, the number of electrons surrounding the central atom in a stable molecule is fewer than eight. Beryllium is an alkaline earth metal and so may be expected to form ionic bonds. However, its very small size and somewhat higher ionization energy compared to other metals actually lead to beryllium forming primarily molecular compounds. Since beryllium only has two valence electrons, it does not typically attain an octet through sharing of electrons. Odd-Electron Molecules: are a number of molecules whose total number of valence electrons is an odd number. It is not possible for all of the atoms in such a molecule to satisfy the octet rule. An example is nitrogen dioxide (NO2). Each oxygen atom contributes six valence electrons and the nitrogen atom contributes five for a total of seventeen. Expanded Octets: Atoms of the second period cannot have more than eight valence electrons around the central atom. However, atoms of the third period and beyond are capable of exceeding the octet rule by having more than eight electrons around the central atom. Starting with the third period, the d sublevel becomes available, so it is possible to use these orbitals in bonding, resulting in an expanded octet. MOLECULE POLARITY Part 6: Two atoms screen Explain all the ways you can change the polarity of the two-atom molecule. Draw this table in your notebook Representation Response to change in Effect on molecule polarity electronegativity Bond Dipole Partial Charges Electrostatic Potential Part 7: Three atoms screen Explain any new ways to change the molecule polarity of the three-atom molecule. How does the ABC-bond angle effect molecule polarity? Tip: Try changing the bond angle in the simulation.
SO2, XeF2, ClF3, SF4, XeF4, BrF5, PCl5, SF6 Exceptions to the octet rule fall into one of three categories: (1) incomplete octet, (2) odd-electron molecules, and (3) an expanded octet. Incomplete Octet: In some compounds, the number of electrons surrounding the central atom in a stable molecule is fewer than eight. Beryllium is an alkaline earth metal and so may be expected to form ionic bonds. However, its very small size and somewhat higher ionization energy compared to other metals actually lead to beryllium forming primarily molecular compounds. Since beryllium only has two valence electrons, it does not typically attain an octet through sharing of electrons. Odd-Electron Molecules: are a number of molecules whose total number of valence electrons is an odd number. It is not possible for all of the atoms in such a molecule to satisfy the octet rule. An example is nitrogen dioxide (NO2). Each oxygen atom contributes six valence electrons and the nitrogen atom contributes five for a total of seventeen. Expanded Octets: Atoms of the second period cannot have more than eight valence electrons around the central atom. However, atoms of the third period and beyond are capable of exceeding the octet rule by having more than eight electrons around the central atom. Starting with the third period, the d sublevel becomes available, so it is possible to use these orbitals in bonding, resulting in an expanded octet. MOLECULE POLARITY Part 6: Two atoms screen Explain all the ways you can change the polarity of the two-atom molecule. Draw this table in your notebook Representation Response to change in electronegativity Effect on molecule polarity Bond Dipole Partial Charges Electrostatic Potential Part 7: Three atoms screen Explain any new ways to change the molecule polarity of the three-atom molecule. How does the ABC-bond angle effect molecule polarity? Tip: Try changing the bond angle in the simulation.
1Molecule%20Shapes.docx