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CEM 141 Exam -3 Questions And Answers Rated A+ New Update Assured Satisfaction
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CEM 141 Exam #3- ANS-For a better understanding of sigma bonds in diamond refer to diagram on slide 20 of
lecture 26.
- ANS-for more information on sigma and pi bonds in graphite refer to the diagram on slide 26
of lecture 26.
- we are made of carbon
-carbon forms 4 bonds
-it forms bonds to C, H, O, N, S, P and lots of others (including halogens: F, Cl, Br, I , At, UU)
-the properties of compounds are emergent (not just the sum of the elements involved) -
ANS-What are some important facts about bonding in carbon?
-a single bond is always a sigma bond
-all the rest are always pi bonds
-sigma bonds allow for rotation around the bond because sigma bond will not change
-pi bonds do not (it would break/change the pi bond)
-each center of electron density needs one hybrid orbital - ANS-Important facts about sigma
bonds and pi bonds.
-atomic orbitals combine to form an equal number of molecular orbitals
-each orbital can contain up to two electrons
-electrons in bonding orbitals stabilize the system
-electrons in anti-bonding orbital make it less stable
-electrons are delocalized - ANS-Explain the molecular orbital model of bonding.
-atomic orbitals hybridize (mix up) to form bonding orbitals that then combine with orbitals from
other atoms to form a bond
-to form 4 bonds-carbon hybridizes the 4 orbitals that are used for bonding
-since one s and three p orbitals combine we call them sp3 orbitals
-they naturally assume a tetrahedral geometry
-when the hybrid orbitals combine there is a large gap between the bonding and anti-bonding
molecular orbitals - ANS-Explain the bonding in diamond using the valence bond model.
-atomic orbitals overlap to form a bond
-the greater the overlap, the stronger the bond
-each bond made up of two electrons
-electrons are localized in the bond - ANS-Explain the valence bond model of bonding.
-C is sp2 hybridized
-contains C-C double bond
, -one sigma bond (sp2-sp2 overlap)
-one pi bond (sideways p-p overlap)
-restricted rotation around double bond - ANS-What are alkenes?
-CH4
-contains four C-H bonds that are equidistant from each other and identical because of the sp3
hybridization on the carbon
-bond angle is approximately 109 degrees
*Know how to draw a model of CH4--> example can be found in lecture 27 notes* -
ANS-Describe methane?
-contains a metal and a non-metal (one element with low electronegativity (metal) and one
element with high electronegativity (non-metal))
-metals form cations, non-metals form anions
-each ion typically achieves noble gas configuration because this is a trade-iff between energy
required to gain or lose electrons, and stabilization of the system when ionic bonding
interactions are formed
-ionic compounds are neutral - ANS-What is a simple ionic compound?
-contains a polyatomic ion: a group of atoms covalently bonded to each other; the entire particle
has a charge
Ex: NH4+ (ammonium ion); CN- (cyanide ion); NO3- (nitrate ion); CO3 2- (carbonate ion); PO4
3- (phosphate ion); CH3COO- (acetate ion) - ANS-What are complex ionic compounds?
-diamond: covalent network
-water: polar covalent molecular (with intermolecular forces)
-metallic - ANS-What kinds of bonding do you know?
-each carbon forms 4 bonds to 4 identical carbons
-the bonds arrange themselves towards the corners of a 4 sided figure (a tetrahedron)
-tetrahedral geometry
-the C-C-C bond angle is 109 degrees - ANS-Explain the bonding in diamond.
-electrons are located in bonds between atoms-not free to roam
-there is a large "band gap" between the bonding and anti-bonding orbitals - ANS-why does
diamond have a high mp and does not conduct electricity?
-electrostatic potential map (big blob)
-space-filling model (still sort of a blob but with more definite shapes)
-ball-and-stick model
-perspective formula
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