burge_ch6_notes

burge_ch6_notes - Chapter 6 Representing Molecules 2011...

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©2011 Donald L. Siegel, All Rights Reserved Chapter 6 Chapter 6 Representing Molecules
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©2011 Donald L. Siegel, All Rights Reserved Octet/Duplet Rule Octet/Duplet Rule W In forming covalent bonds, atoms share enough electrons to complete their valence shell (8 electrons except for H or He which take 2) W Shared elecrons (as pairs) are called bonding pairs W Pairs of electrons that are not shared are called lone pairs
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©2011 Donald L. Siegel, All Rights Reserved Lewis structures Lewis structures W Show all the valence electrons W Bonding pair are represented by dashes W Lone pairs are indicated by : W The electrons do not have to be where they started Step 1: Count all the electrons in the valence shell of all the atoms Step 2: Start pairing up unpaired electrons in various atoms to complete the octets of all the atoms
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©2011 Donald L. Siegel, All Rights Reserved Multiple Bonds Multiple Bonds W What if a pair of atoms shares more than 2 electrons? Many bonds include more than 2 electrons. Each pair we call a bond. So 2 pairs between the same atoms we call a double bond. O=O N N
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©2011 Donald L. Siegel, All Rights Reserved Examples Examples
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©2011 Donald L. Siegel, All Rights Reserved
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©2011 Donald L. Siegel, All Rights Reserved Extra energy? Extra energy? W It takes 436 kJ to pull apart H 2 and 159 kJ to separate F 2 W Thus it should take (436+159)/2 = 298 kJ separate H-F W It actually takes 565 kJ W Where does the extra energy come from? In addition to the energy from the chemical bond, there is some electrostatic interaction The F is partly negative and the H is partly postive W Linus Pauling developed a scale based on the sum of the electron affinity and the ionization energy
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©2011 Donald L. Siegel, All Rights Reserved What What electronegativity electronegativity means means W The more electronegative an atom is, the strong the pull on the electron pair W The thing that matters is the difference in electronegativity If one atom is enough more electronegative, the electrons spend all the time around that atom (ionic) If the difference is zero, the electrons are shared equally (covalent)
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©2011 Donald L. Siegel, All Rights Reserved
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©2011 Donald L. Siegel, All Rights Reserved Ionic vs. covalent Ionic vs. covalent W By combining electron affinity and ionization energy, we get a predictor or
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burge_ch6_notes - Chapter 6 Representing Molecules 2011...

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