Lewis Dot Structures

1
Lewis Dot Structures

• Putting atoms together to make compounds

2
Single Atom Lewis Structures

• What do they look like? (instructor will draw one
  on the board)
• Procedure
• Write element symbol
• Add valence electrons (dots) around element
  symbol
• If valence electrons are paired in an orbital,
  pair them on the structure, if not, dont (keep
  them single)
• Do Carbon on the board
• More Practice H, He, F, P, Mg, N, Kr

3
Lets Put Them Together!Ionic bonds (Salts!!!)

• Transfer of one or more electrons from one
  species to anotherUsually A Metal Nonmetal
• Can be combinations of Polyatomic Ions (will
  explain these later)
• They Make Ionic Lattices! LiF Li F-
• (Graphic on Next Slide)

4
A Lithium Fluoride Crystal
5
Another Representation of Crystals (aka Ionic
Lattices)
6
Ionic Lattices are also called Salts!

• The representative formulas are called Formula
  Units (the simplest way to express what is in the
  crystal).
• Every element has to have 8 electrons (or 2 in
  some casesmore about that later) when bonding
  with another one.
• We transfer dots (e-) from one Lewis Structure to
  another to make Ionic Bonds.
• Put every ion in brackets R and its charge
  outside the brackets when finished.
• Show example on board

7
Periodic Chart Charges

• (1) Alkali Metals1
• (2) Alkaline Earth Metals2
• (3-12) Transition MetalsMany Possible Chargesif
  you do these, you will be given the charge to
  use!
• (13) Boron Family3

8
Periodic Chart Charges (cont)

• (14) Carbon Family4
• (15) Nitrogen Family3-
• (16) Oxygen Family2-
• (17) Halogen (or Halides) Family1-
• (18) Noble GasesNo Charge ?
• These are only TRENDS!

9
Draw Lewis Structures

• Examples to do in class NaCl, RbBr, MgI2, LiF,
  Na2O
• Problem Set MgCl2, NaI, Ca3N2, SrBr3, Rb2O, HCl,
  HeI (Draw Lewis Structures for ones that are
  possible, label Doesnt Work for ones that are
  not)

10
Covalent Lewis Structures (nonmetalnonmetal)

• Called Molecules!
• Share valence electrons.
• Occur in single, discrete (not attached to
  anything else) structures.
• Here are 4 molecules of C2H6 (ethane)
• Notice they are not attached to each other like
  salts!!!

11
Covalent Lewis Structures Procedure

• Sum the valence electrons for entire molecule.
• Put two electrons between central and adjacent
  atoms.
• Using a line to represent a pair of bonding
  electrons, draw in a single bond between atoms.

12
Covalent Procedure (cont)

• Distribute the remaining electrons to achieve a
  noble gas configuration (8 or 2 e-) for each
  element
• Duet Rule H and He
• Octet Rule All other elements.
• Electrons only travel in pairs!

13
Hints for Success!

• No rings (circles, triangle, etc) except for
  Hydrocarbon Molecules
• The single element usually goes in the middle.
• If single bonds will not work, try double bonds
  (first) and then triple bonds (second).

14
For Polyatomic Ions (nonmetal-nonmetal w/ charge)

• () sign means subtract one e- from molecule
  total.
• (-) sign means add one e- to molecule total.
• Do NO3- (nitrate) and C2O42- (oxalate) on board

15
Exceptions to the Rules ?

• Boron family can have only six e- if they have
  to.
• Elements from 3p and down can have more than 8 e-
  if they have to.
• Examples Water, CO2, CN-, HF, N2, NH4CH4, CF4,
  and NO
• Homework O2, O3, H2, F2, Cl2, PF3, XeO4, SeF2,
  POCl3, C2H4, PH3, CH3Cl, C2H2, N2O, NCS, NH3, He2

16
Ionic/Covalent Combinations

• Figure out which polyatomic ions are present
  (there will be more than two different elements
  and is not a hydrocarbon)
• Draw Lewis Structure for the polyatomic ion and
  then for the other ion.
• Put them together (remember the brackets!)
• Problem Set NaNO3, CaSO4, Li2C2O4, NH4ClO3,
  LiBrO3