11/3/09

Test Tomorrow

- 40 questions, no calculations
- Know where the groups in the periodic table are and know their names
- Be able to give examples of electron configuration

Exceptions to the Octet Rule

• Exceptions to the octet rule include those for atoms that cannot fit eight electrons, and for those that can fit more than 8 electrons, into their outermost orbital
• Hydrogen - forms bonds in which it is surrounded by only two electrons
• Boron - has just three valence electrons, so it tends to form bonds in which it is surrounded by six electrons
• Main group elements in periods three and p can form bonds with expanded valence, involving more than eight electrons

Electron-Dot Notation

• to keep track of valence electrons, it is helpful to use electron-dot notation
• electron-dot notation is an electron configuration notation in which only the valence electrons of an atom of a particular element are shown, indicated by dots placed around the element's symbol. the inner shell electrons are not shown

Lewis Structures

• electron-dot configuration can also be used to represent molecules (ex. H:H)
• the pair of dots between symbols represents the shared electron pair of the Hydrogen-Hydrogen covalent bond
• for a molecule of fluorine, F2, the electron-dot notations of the two fluorine atoms are combined
• an unshared pair, also called a lone pair, is a pair of electrons that is not involved in bonding and that belongs exclusively to one atom
• the pair of dots representing a shared pair of electrons in a covalent bond is often replaced by a long dash (ex. H-H)
• a structural formula indicates the kind, number, and arrangement, and bonds but not the unshared pairs of atoms in a molecule