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CEM 141 Exam -3 (1) Questions & 100% Verified Correct Answers with complete solutions (Latest update $7.99   Add to cart
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CEM 141 Exam -3 (1) Questions & 100% Verified Correct Answers with complete solutions (Latest update

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CEM 141 Exam -3 (1) Questions & 100% Verified Correct Answers with complete solutions (Latest update

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  • August 15, 2024
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  • 2024/2025
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  • cem 141 exam 3 1

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CEM 141 Exam #3
3-D extended continuous network (shown on tables in notes in red); continuous materials have
higher boiling and melting points than discrete - ANS-What are continuous materials?

small atoms/molecules (shoes on tables in notes in black) - ANS-What are discrete materials?

H2: LDF
He: LDF
Li: metallic bonds (no LDFs in metals) move metal cores relative to one another
c: covalent - ANS-Using the table found on lecture 25 slide 13 what kinds of interactions must
be overcome in order to melt: H2, He, Li, and C?

diamond, graphite, lonsdaleite (not common), buckminsterfullerene, C540, C70, amorphous
(soot), carbon (nanotube) - ANS-What are the allotropes of carbon?

high melting point; hard; brittle (breaks alongs planes); translucent (lets light through); does not
conduct electricity - ANS-What are some characteristics of diamond?

high melting point; soft; slippery; grey, shiny; conducts electricity; opaque - ANS-What are some
characteristics of graphite?

because the arrangement of atoms is different the bonding is different - ANS-Diamond and
graphite are made out of carbon atoms only--how can they have such different properties?

-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.

all of those covalent bonds would have to be overcome; would require a lot of energy, therefore,
diamond does not really melt it decomposes - ANS-If you wanted to "melt" diamond (tetrahedral
carbon) what would have to happen?

metals melt because they have metallic bonds and a sea of electrons that can easily move
about - ANS-why do metals melt and diamonds do not?

bonds; localized - ANS-To explain bonding in carbon, we use valence bond theory to assume
that the atomic orbitals overlap to form _________________.
we consider the bonds to be ___________________ between the two bonded atoms (not like in
MO theory).

, -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 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.

[He] 2s2 2p2 (1 s orbital and 3 p hybridize to make 4 sp3 orbitals) - ANS-What is the electron
configuration of carbon?

using the electron configuration we know a C atom has 4 valence electrons in different types of
orbitals; electrons in a filled s orbital and two half-filled p orbitals
-should give different types of bonds, but the evidence indicates that all four bonds are identical,
therefore, it uses hybrid orbitals - ANS-How can carbon form 4 identical bonds in diamond?

hybrid - ANS-# atomic orbitals in = # ______________ orbitals out

4 - ANS-How many atomic orbitals (on one carbon) should combine to make 4 hybrid orbitals?

-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.

strong directed bonds; these bonds give rise to high mp/decomposition temperature--because
these bonds have to be broken to melt diamond

*these bonds are sigma bonds* - ANS-What do hybridized atomic orbitals (sp3) give rise to?

- ANS-For a better understanding of sigma bonds in diamond refer to diagram on slide 20 of
lecture 26.

3D network of strong bond, you would have to break bonds to disrupt a crystal - ANS-Why is a
diamond hard?

-electrons are located in bonds between atoms-not free to roam

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