Chemical Bonding: By: Ms. Buroker

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Chemical BondingBy Ms. Buroker
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• Imagine getting onto a crowded elevator. As
  people squeeze into the confined space, they come
  in contact with each other. Many people will
  experience a sense of being too close together.
• When atoms get close enough, their outer
  electrons repel each other. At the same time,
  however, each atoms outer electrons are strongly
  attracted to the nuclei of the surrounding atoms.
• The degree to which these outer electrons are
  attracted to other atoms determines the kind of
  chemical bonding that occurs between the atoms.

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Chemical Bonding

• The force that holds two atoms together is
  known as a chemical bond.

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Compounds are formed from chemically bound atoms
or ions
Substances become more stable through chemical
bonding, where 2 or more atoms are joined
together by a simultaneous attraction.
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Bonding involves only the valance electrons.
Na
Cl
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Ionic Bonds
Chemical Bonding that results from the electrical
attraction between cations and anions is called
ionic bonding.
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Ionic Bonds
When you consider that for an ionic bond to form
there must be a difference in charge between the
ions, can you predict what two types of atoms
allow this to occur?
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Ionic Bonds
Non- Metals
Metals
Ionic Bonding occurs between metals and
non-metals. This happens when metals lose an
electron(s) (positive charged ion) and non-metals
gain electron(s) (negatively charged ion). of
e- transferred of valance e-
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Ionic Bonds
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What is the Octet Rule?

• That atoms have a tendency toward a full
  valence shell with 8 e-.

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Why Do Atoms Bond In The First Place?

• Metals and non- metals react to form ionic
  compounds electrons are transferred in order
  for both atoms to have a full valence shell.
• BUT!!!!!!!!!!!!!!!
• Sometimes two atoms both need to gain
  electrons and can have an attraction for the
  valence electrons. Sharing of electrons is
  another way in which atoms can bond!

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Covalent Compounds

• Covalent Bonds are those chemical bonds that
  result from the sharing of electrons.

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Ionic or Covalent
In pure ionic bonds- electrons are completely
given away to other atoms. In pure covalent
bonds- electrons are totally owned by both
atoms. It turns out neither is completely
true. In actuality, the truth lies somewhere in
between. What makes the difference is how
strongly the atoms of each element attract
electrons.
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Electronegativity
Electronegativity is a measure of the ability of
an atom in a chemical compound to attract
electrons from another atom in the compound.
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Electronegativity
We can use Electronegativity values to determine
whether a compound is ionically bound or
covalently bound.
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Factors Determining Electronegativity
When you subtract the electronegativity values of
two atoms bound together you use the value to
determine what kind of bond you have. Non-polar
covalent 0-0.3 Polar Covalent Bonds 0.3- 1.7
Ionic Bonds 1.7- 3.3
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Covalent Bonds
Polar- Covalent Bond a covalent bond in which
the bonded atoms have an unequal attraction for
the shared electrons. Non-polar covalent Bond a
covalent bond in which the bonding electrons are
shared equally by the bonded atoms, resulting in
a balance distribution of electrical charge.
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Molecules
When compounds are covalently bonded, they form
molecules.
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Molecular Formula
When we have molecules we have to write their
formula, or what theyre made of. Molecular
Formulas show the type and numbers of atoms
combined in the covalently bonded compound.
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Covalent Bond Formation
Everything in nature favors stability covalent
bonds form from a need for stability. There is a
perfect distance apart the atoms need to be.
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Structural Properties
The strength of covalently bound compounds or
molecules depends on distance separating the
atoms (size will affect this).
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Property Factors

• There are two factors we have to think about
  when dealing with bonds of any kind.
• 1.) Bond Length
• 2.) Bond Energy- the amount of energy it takes to
  break a bond.

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Property Factors
What relationship can you observe on page 182 of
your book where the bond lengths and bond
strengths are listed?
In general the Longer the bond length the
weaker the bond!!! The opposite is true, shorter
bond lengths tend to be stronger!!
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Electron Dot Structures and Lewis Structures
We use electron dot structures as a way to
symbolize the number of valance electrons an atom
has.
6e-
7e-
To put it simply, Lewis Structures are our way of
explaining how atoms in a covalent bond share
their valance electrons. Its our best guess at
whats going on in the covalent bonding process.
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Lewis Structures

• Lewis structures use dots and/or dashes to
  represent bonding pairs of electrons and what we
  call lone pairs (electrons not directly involved
  in bonding.

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Drawing Lewis Structures

• Step 1 Sum the valence electrons from all the
  atoms- this is how many electrons are available
  for sharing.
• Step 2 Draw the skeletal structure for the
  compound and bond all the terminal atoms to the
  central atom- the central atom is in general, the
  least electronegative atom. Hydrogen will always
  be a terminal atom
• Step 3 Complete the octet for each atom-
  hydrogens octet is 2 e-, in general, other atoms
  need 8 e-
• Step 4 Once every atom is happy, if there are
  too many electrons being shown, multiple bonds
  will be needed (double, or triple)
• Step 5 Once every atom is happy, If there are
  electrons are left over, then add the extra
  electrons to the central atom

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Exceptions to the Octet Rule

• 1.) Be 4e-
• 2.) B 6e-
• 3.) Elements Beyond Period 2 can hold more than
  8e-, they can accommodate 10 or even 12e- if they
  have to..

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Structural Properties

• During the formation of an ionic compound, the
  positive and negative ions are packed into a
  regular repeating pattern that balances the
  forces of attraction and repulsion between ions
  this is known as ionic crystal.

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Crystal Lattice
We call this three dimensional arrangement of
ions a crystal lattice.
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Crystal Lattice Properties

• High Melting Points and Boiling Points
• Hard, Rigid, Brittle
• They form Electrolytes

Electrolytes are solutions that conduct
electricity.
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Lattice Energy

• The energy required to separate one mole of
  the ions of an ionic compound . In other words
  how strong are the forces holding the ions in
  place?
• There is a relationship between lattice energy
  and the interionic distance.

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Graphically Determine the Relationship Between
the ionic radii and Lattice Energy

• LiF, LiCl, LiI
• Li 76pm, F- 133pm, Cl- 181pm, I- 220pm
• LiF -1032kJ/mol
• LiCl -852 kJ/mol
• LiI -761 kJ/mol
• X-axis ionic radii
• Y- axis lattice energy (use as a positive value)

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Lattice Energy Continued

• The value of lattice energy is also affected
  by the charge of the ion .
• The ionic bond formed from the attraction of
  ions with larger positive or negative charges
  generally has a more negative lattice energy.

  Lattice Energy   Lattice Energy
Compound (kJ/mol) Compound (kJ/mol)
KI -632 KF -808
KBr -671 AgCl -910
RbF -774 NaF -910
NaI -682 LiF -1030
NaBr -732 SrCl2 -2142
NaCl -769 MgO -3795
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Predict

• List the following compounds in order of
  increasing melting point in ?C
• KBr
• KI
• KF
• KCl