CHEM151Chapter 7

Chemistry (MasteringChemistry Series)

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10/7/2008 1 C HAPTER 7 Covalent Bonds 1 and Molecular Structure C OVALENT B OND  There is an optimum distance that will maximize attraction. This is the bond length: calculated by adding the radii of two atoms. S TRENGTHS OF C B ONDS  Closer nuclei result in a stronger bond. Shorter bond = stronger bond.  Energy is required (absorbed) to break a bond Energy is required (absorbed) to break a bond. Energy is given off (released) when a bond is formed.
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10/7/2008 2 DIFFERENCES IN COVALENT BONDS  Covalent bond: electrons shared between atoms  Atoms don’t always share electrons equally  Electronegativity : the ability of an atom in a molecule to attract e to itself. What other atomic property does this remind you of?  Pauling found that HF has a stronger bond than the average of the H 2 and F 2 bonds. He attributed this extra strength to partial ionic character. ~ From bond strengths, he assigned relative values of electronegativity 4 E LECTRONEGATIVITY (EN) P OLAR OR N ONPOLAR ?  Bonds can be found with a range of polarities, from nonpolar covalent (F 2 , CH) to polar covalent (HF) to ionic (LiF). The greater the difference in EN, the more ionic a bond is.  Red = high electron density  Blue = low electron density  Green = in between 6
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10/7/2008 3 BONDING  Identify the type of bond (ionic, polar covalent, nonpolar covalent) holding atoms together in the following compounds.  NaCl Electronegativities  H 2  PCl 3  H 2 O  CaBr 2  CH 4  NaNO 3 H 2.1 N 3.0 Na 0.9 O 3.5 Ca 1.0 Cl 3.0 P 2.1 Br 2.8 C 2.5 F 4.0 M ORE E XAMPLES  Identify the type(s) of bonds (ionic, polar covalent, nonpolar covalent) holding atoms together in the following compounds:  MgCl 2  NCl 3  MgCO 3  Cl 2 L EWIS D OT S YMBOLS  Covalent bonding focuses on interactions of valence electrons of two or more atoms  Can use Lewis Dot Symbols to represent the numbers of valence electrons for each atom (based on electron configurations)
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10/7/2008 4 E LECTRON -D OT S TRUCTURES  Used to show how electrons are shared between nonmetals in a covalent bond. Use valence electrons to give each atom an octet, with a few exceptions (e.g., H). M OLECULES & I ONS WITH L EWIS S  1 st given Molecular Formula  2 nd Identify center atom ~ Lower group number in the center (lower electronegativity) ~ Usually the first one in formula is center  3 rd draw a bond from the center atom to each surrounding atom  4 th Using dots draw the lone pairs ~ make sure each atom has the correct # of electrons it started with  5 th Verify each atom obeys the octet rule M L S C ONT .  Tips or shortcuts ~ H–one bond ~ C – 4 bond C – 4 bonds ~ N–3 bonds ~ O–2 bonds ~ Halogens–1 bond when they are surrounding atoms (F is always a surrounding atom)
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10/7/2008 5 S INGLE B ONDS  Single bond represented as H:H or H H  : 14 valence electrons tota F 2 : 14 valence electrons total . . .
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CHEM151Chapter 7 - 10/7/2008 C HAPTER 7 Covalent Bonds and...

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