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Chemical Bonding

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Chemical Bonding Chapter 12 Determining Bond Polarity Look up the electronegativities of both atoms involved in the bond. If there s a difference, it s a polar bond. – PowerPoint PPT presentation

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Title: Chemical Bonding


1
Chemical Bonding
  • Chapter 12

2
May the force be with you
  • Chemical Bond The force that holds 2 or more
    atoms together and makes them function as a unit.
    (Intramolecular force)
  • Bond Energy The energy required break a given
    chemical bond

3
Types of Chemical Bonds
  • Ionic Bonding Electrons are transferred from one
    atom to another. (Ions are formed)
  • Metal Non Metal

4
  • Covalent Bonding Electrons are shared between
    atoms (NO ions)
  • nonmetal nonmetal

5
Some at ms dont like to share.
  • Electronegativity Tendency of an atom to attract
    electrons in a chemical bond.

6
If one atom in a bond has a greater
electronegativity
  • Polar Covalent Bond Unequal sharing of
    electrons.
  • The electrons still are not completely
    transferred!

Covalent
Polar Covalent
Ionic
7
Determining Bond Polarity
  • Look up the electronegativities of both atoms
    involved in the bond.
  • If theres a difference, its a polar bond.
  • The bigger the difference, the more polar.
  • Polar bonds?
  • O-H, S-H, P-S, F-S, N-O, H-H

8
Representing Polar Bonds
A dipole is drawn with a plus sign on the
lower electronegative element with an arrow
going towards the more electronegative element.
9
More dipoles
More on what polarity means to molecules to come
in later units.
10
A closer look at ionic bonding
  • A few observations

Plus, the noble gases dont react. What does it
all mean?
11
Lets look at the e- configurations
See a pattern?!??!?
12
The envy of the all the elements the noble gases
  • When atoms become ions they want to have a noble
    gas electron configuration
  • Metals lose electrons to reach noble gas
    configuration
  • Nonmetals gain electrons to reach noble gas
    configuration
  • But what do ionic compounds look like?

13
LiF
14
(No Transcript)
15
What about nonmetals?
  • A few things to remember
  • ONLY THE VALENCE ELECTRONS ARE INVOVLVED IN
    CHEMICAL BONDING!!
  • ATOMS WANT TO ACHIEVE A NOBLE GAS e-
    CONFIGURATION
  • A Lewis Structure is a representation of a
    molecule that shows how the valence electrons are
    arranged among the atoms in the molecule

16
Back to noble gases
  • Neon 1s22s22p6 8 valence electrons
  • Argon 1s22s22p63s23p6 8 valence e-
  • Xenon 1s22s22p63s23p64s23d104p6 8 valence e-
  • See a pattern?
  • Octet Rule Atoms (except for hydrogen helium)
    want to be surrounded by 8 electrons in the
    valence principle energy level.
  • Hydrogen and helium want to be surrounded by 2
    valence electrons, known as the duet rule

17
Steps for writing Lewis Structures
  • Obtain the sum of the valence electrons from all
    of the atoms. Do not worry about where the
    electrons come from, just find the sum.
  • Use one pair of electrons (or a line) to form a
    bond between each pair of bound atoms.
  • Arrange the remaining electrons to satisfy the
    octet (or duet) rule.
  • Check to make sure you have the right number of
    electrons and that each atom as the octet rule
    satisfied.

18
Your first Lewis StructureF2
Lone Pairs of e- -Nonbonding pairs -Not
involved with the bonding
Electrons
F
F
More lone pairs
Bonding Electron Pair Shared Between Both Atoms
19
Often, a line will represent a bonding pair of
electrons

F
F
F F
20
Lewis Structure for Water
21
Atoms that really like to share
  • Single bond covalent bond in which 1 pair of
    electrons is shared by 2 atoms
  • Double bond covalent bond in which 2 pairs of
    electrons are shared by 2 atoms
  • Triple bond covalent bond in which 3 pairs of
    electrons are shared by 2 atoms

22
Resonance
  • A molecule shows resonance when more than one
    Lewis structure can be drawn for the molecule

23
What about polyatomic ions?
  • Same rules apply as with molecules, only add or
    subtract the charge of the ion from the total
    valence electrons.
  • Draw the Lewis Structure for CN-
  • Hint There are 10 total valence electrons.

24
C N -
NOTE The Lewis Structure is put in brackets
with the charge outside of it to indicate that
the structure is an ion.
25
There are a few exceptions
  • BF3
  • NO
  • NO2

26
Were going 3D!
  • What do these molecules look like?
  • What is their shape?
  • VSEPR Theory
  • VSEPR Valence Shell Electron Pair Repulsion
  • Electrons have the same charge, so they repel
    each other.
  • VSEPR works on putting electron pairs (both
    bonding and lone pairs) as far apart from each
    other.

27
Steps for VSEPR Theory
  • Draw the Lewis Structure
  • Count the electron pairs and arrange them so that
    they are as far apart from each other as possible
  • Determine the positions of the atoms from where
    the bonding electron pairs are shared.
  • Name the molecular structure based on the
    positions of the atoms

28
Oh the possibilities
29
Remember
  • A double or triple bond acts as a single electron
    pair in VSEPR

30
Polar Bond Polar Molecule?
  • What is a polar bond?
  • Nonpolar bonds never produce polar molecules
  • Polar bonds usually produce polar molecules,
    unless the polar bonds cancel each other out.
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