Review GUide #1

Review GUide #1 - Chem 1057 J Walcott Page 1 LEARNING...

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Chem 1057 Page 1 J. Walcott LEARNING STRATEGIES CENTER Fall 2011 Review Guide #1 Lectures: 8/24/11 – 8/26/11 Chapters 1 and 2 I. Review of Concepts from General Chemistry A. Valence electrons are those in the outermost shell in an atom. The tendency of some atoms to gain, lose or share valence electrons to achieve the noble-gas configuration is known as the octet rule . B Understand the distinction between an ionic bond and a covalent bond . C. You should be able to write line bond (Lewis or Kekule) structures to represent the bonding in simple covalent molecules, including molecules containing double bonds or triple bonds. The general procedure outlined below usually works: 1. Find the total number of valence electrons contributed by all atoms in the molecule. Add one electron for each negative charge. Subtract one electron for each positive charge. 2. Make connections between atoms. The least electronegative atom is usually in the center (note that hydrogen is never the central atom in a molecule). 3. Complete octets around outer atoms by placing lone pairs. 4. If valence electrons remain, place them around the central atom as lone pairs. 5. If no electrons remain, but if the central atom does not have an octet, form enough multiple bonds to give it an octet. Since organic molecules typically only involve a small subset of the main group elements, it is useful to know the number of bonds (the valency) of the elements most commonly encountered in neutral organic molecules: C = 4 bonds; H = 1 bond; O = 2 bonds; N = 3 bonds; halogens = 1 bond. D. You should be able to calculate formal charge: Formal charge = valence electrons in isolated atom non-bonded electrons number of bonds E. Electronegativity is the tendency of an atom to attract electrons to itself in a covalent bond. A bond is polar when electrons are shared unevenly. Electronegatively can sometimes be used to predict whether a bond is ionic, polar covalent and non-polar covalent. F. An atomic orbital is a description of the wave properties of an electron in an atom. A three- dimensional region of space in which the electron is most likely to occur characterizes each
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Review GUide #1 - Chem 1057 J Walcott Page 1 LEARNING...

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