Molecular Compounds and Covalent Bonding

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Molecular Compounds andCovalent Bonding
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Ionic Bonding quick review

• Involve positive ions (cations) and negative ions
  (anions). Usually contains a metal ion (cation)
  and a non-metal ion (anion). Remember, opposites
  attract!
• Ions will gain or lose electrons to achieve a
  noble gas configuration (full s and p orbitals).
• Metals lose electrons and non-metals gain
  electrons.
• Ionic compounds form crystals with high melting
  points.

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Ionic vs. Covalent bonding

• Both types of bonding still obey the octet rule.
  The difference is how the octet is achieved.
• Ionic compounds involve a transfer of electrons
  from the cations to the anions.
• Covalent bonding entails a sharing of electrons.
• Covalent bonding usually occurs between
  nonmetals.

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Electronegativity differenceis the key.

• electronegativity is an atoms ability to attract
  electrons to itself when bonded.

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Percent Ionic Character

• Greater EN difference, the more ionic
• Less EN difference, the more covalent

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Classifying bonds

• The type of atoms and their EN difference
  determine the type of compound and bond type
• Ionic 1.67
• Covalent ( 2 types)
• Polar covalent (electrons not shared equally)
• gt .2 but less than 1.67
• Non-polar covalent (electrons shared equally) .2

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Classifying and naming Compounds
The system for naming an ionic compound is
different from that for naming a covalent
compound, so before a compound can be named, it
must be classified as ionic or covalent using the
EN difference.
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Naming Covalent Compounds
Covalent compounds are named by adding prefixes
to the element names.
A prefix is added to the name of the first
element in the formula if more than one atom of
it is present. (The less electronegative element
is typically written first.)
A prefix is always added to the name of the
second element in the formula. The second element
will use the form of its name ending in ide.
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Naming Covalent Compounds
Prefixes
Note When a prefix ending in o or a is added
to oxide, the final vowel in the prefix is
dropped.
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Naming Binary Covalent Compounds Examples
N2S4
dinitrogen tetrasulfide
NI3
nitrogen triiodide
XeF6
xenon hexafluoride
CCl4
carbon tetrachloride
P2O5
diphosphorus pentoxide
SO3
sulfur trioxide
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Naming Compounds Practice
SiF4
silicon tetrafluoride
two nonmetals ? covalent ? use prefixes
Na2CO3
sodium carbonate
metal present ? ionic ? no prefixes Na ? group I
? no Roman numeral
N2O
dinitrogen monoxide
two nonmetals ? covalent ? use prefixes
K2O
potassium oxide
metal present ? ionic ? no prefixes K ? group I
? no Roman numeral
Cu3PO4
copper (I) phosphate
metal present ? ionic ? no prefixes Cu ? not
group I, II, etc. ? add Roman numeral (PO4 is 3-,
each Cu must be 1)
CoI3
cobalt (III) iodide
metal present ? ionic ? no prefixes Co ? not
group I, II, etc. ? add Roman numeral (I is 1-,
total is 3-, Co must be 3)
PI3
phosphorus triiodide
two nonmetals ? covalent ? use prefixes
NH4Cl
ammonium chloride
NH4 ? polyatomic ion present ? ionic ? no
prefixes
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Writing Formulas for Covalent Compounds
The names of covalent compounds contain prefixes
that indicate the number of atoms of each element
present.
If no prefix is present on the name of the first
element, there is only one atom of that element
in the formula (its subscript will be 1).
A prefix will always be present on the name of
the second element. The second element will use
the form of its name ending in ide
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Writing Formulas for Binary Covalent Compounds
Examples
nitrogen dioxide
NO2
diphosphorus pentoxide
P2O5
xenon tetrafluoride
XeF4
sulfur hexafluoride
SF6
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Writing Formulas Practice
carbon tetrafluoride
CF4
prefixes ? covalent ? prefixes indicate subscripts
Na3PO4
sodium phosphate
metal ? ionic ? balance charges ? 3 Na1 needed
for 1 PO43-
Cu2SO4
copper (I) sulfate
metal present ? ionic ? balance charges ?2 Cu1
needed for 1 SO42-
Al2S3
aluminum sulfide
metal present ? ionic ? balance charges ?2 Al3
needed for 3 S2-
N2O5
dinitrogen pentoxide
prefixes ? covalent ? prefixes indicate subscripts
NH4NO3
ammonium nitrate
polyatomic ion present ? ionic ? balance charges
? 1 NH41 needed for 1 NO31-
PbO2
lead (IV) oxide
metal present ? ionic ? balance charges ?1 Pb4
needed for 2 O2-
Fe2(CO3)3
iron (III) carbonate
metal present ? ionic ? balance charges ?2 Fe3
needed for 3 CO32-
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Covalent Bonding

• Hydrogen and nonmetals of Groups 4,5,67 often
  become stable and gain noble gas electron
  configurations by sharing electrons to form
  covalent bonds. Atoms will usually share
  electrons to follow the octet rule or the duet
  rule

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• When atoms share one pair of electrons to form a
  covalent bond, it is called a single covalent
  bond. The electrons shared between the atoms are
  a shared pair. A dash instead of two dots is
  used to represent the shared pair. Any other
  electrons on the atoms are unshared pairs or
  lone pairs.

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Rules for Writing Lewis Structures

• Add up the valence electrons from all the atoms
  (Look at group ). Dont worry about keeping
  track of which electrons come from which atoms.
• Use a pair of electrons to form a bond between
  each pair of bound atoms.
• Arrange the remaining electrons to satisfy the
  duet rule for Hydrogen and octet rule for
  everything else
• If necessary, change bonds to double or triple.

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VSEPR

• VSEPR stands for Valence Shell Electron Pair
  Repulsion.  
• Basically, the idea is that covalent bonds and
  lone pair electrons like to stay as far apart
  from each other as possible under all
  conditions. 
• This is because covalent bonds consist of
  electrons, and electrons don't like to hang
  around next to each other much because they have
  the same charge (like charges repel).

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• VSEPR explains why molecules have their shapes. 
  If carbon has four atoms stuck to it (as in CH4),
  these four atoms want to get as far away from
  each other as they can.  This isn't because the
  atoms necessarily hate each other, it's because
  the electrons in the bonds hate each other. 
  That's the idea behind VSEPR.

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Molecular Geometry Hybridization