CHEM 1150 Lecture Notes - Oxonium Ion, Fluorine, Beryllium

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27 Apr 2018
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Step 1: (count up)
Step 2: think about atom placement (more complicated b/c more than
one atom)
Step 5: (for H by sharing lone pairs and making additional bonds)
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Very important rules:
Hydrogen and fluorine (v electronegative and will never form a double
bond to anything) form a single bond and are ALWAYS surrounding
atoms!
1)
Carbon atoms form (at most) 4 bonds always!
2)
Sometimes 3 but never 5
Nitrogen atoms typically form 3 bonds (sometimes 4)!
3)
Oxygen atoms like to form 2 bonds (sometimes 1 and 3 [like oxonium])!
4)
Halogens form 1 bond IF they are surrounding atoms but multiple if they
are central atom! But remember: fluorine is always a surrounding atom
(see 1)!
5)
-
Octet Rule Exceptions:
Electron Deficient Molecules:
2 elements need to keep in mind: Be (Beryllium) ok w/ 4 and B
(Boron) w/ 6
Ex:
®
§
Expanded Octets
S, P, Cl, Br, I, or At
Esp P, S, Cl
§
Period 3 or higher elements; they contain an empty d orbital that
can accommodate more electrons
§
Odd Electron Molecules
NO2
§
They contain a lone un-paired electron which makes them
paramagnetic
§
We call them free radicals
§
-
Lewis Structures for Charged Molecules
SO42-
§
Valence electrons from periodic table
§
Non-bonding valence electrons around atoms
§
Bonding electrons: # of electrons in bonds/ 2
§
Formal charge= valence electrons- non-bonding- bonding electrons
§
Add up all charges (the ones by each atom) and get the 2- on SO4
§
So resonance to try another Lewis Structure
Move outer electrons to middle to form double bonds
(that's the green)
®
§
-
Video notes: CHEM 1150 S18 Molecular Lewis
Structures
Wednesday, April 11, 2018
12:25 AM
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Document Summary

Step 2: think about atom placement (more complicated b/c more than one atom) Step 5: (for h by sharing lone pairs and making additional bonds) Hydrogen and fluorine (v electronegative and will never form a double bond to anything) form a single bond and are always surrounding atoms! Carbon atoms form (at most) 4 bonds always! Nitrogen atoms typically form 3 bonds (sometimes 4)! Oxygen atoms like to form 2 bonds (sometimes 1 and 3 [like oxonium])! Halogens form 1 bond if they are surrounding atoms but multiple if they are central atom! But remember: fluorine is always a surrounding atom (see 1)! 2 elements need to keep in mind: be (beryllium) ok w/ 4 and b (boron) w/ 6. Period 3 or higher elements; they contain an empty d orbital that can accommodate more electrons. They contain a lone un-paired electron which makes them paramagnetic. Bonding electrons: # of electrons in bonds/ 2.

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