Chemistry

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Chemistry

• Ionic Compounds

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Ionic Compounds
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Recall Ions

• on the left (metals) because they lose
  electrons (become less negative)
• - on the right (non-metals) because they gain
  electrons (become more negative)
• What is the total charge if you have X1 and Y-1
• (1) (-1) 0, therefore the total charge is
  neutral or 0

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Ionic Compounds
Ionic Compounds

• Metal and a non-metal combine to form "Ionic
  Compounds".
• The metal atoms loses electrons to form positive
  ions.
• The non-metal gains the electrons to form
  negative ions.
• The two ions join together
• The result is an electrically neutral ionic
  compound.
• Ion Ion Ionic Compound

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Ionic Compounds
Ionic Compounds

• Ionic compounds are formed when a metal gives one
  or more of its electrons to a non metal.
• When all of the electrons are gone, the metals
  inner orbit of electrons is full. So, the metal
  is stable.
• The Lewis diagram is just the symbol and the
  charge
• The atom has lost electrons so it takes on a
  positive charge

Ca2
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Ionic Compounds
Ionic Compounds

• The non-metal receives one or more electrons to
  fill its outer shell and become stable.
• If we draw the Lewis Structure for a non metal we
  include the full valence orbit, brackets and a
  charge
• Having gained two electrons, the Oxygen is now
  negative.
• The resulting positive metal and negative
  nonmetal stick together by electrostatic
  attraction.

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Ionic Compounds
Ionic Compounds

• Putting the compound together, we can see that
  the overall molecule has a neutral charge (no
  charge).
• This particular example is simple because the
  Calcium and Oxygen want to exchange the same
  number of electrons.
• What would happen if they wanted to exchange
  different numbers of electrons?

Ca2
2 2 0
Try it! Li and O
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Using Lewis StructuresIonic bonding between
Lithium and Oxygen

1. First draw the Lewis structures of the atoms on
   their own.
2. Now use an arrow to show the electron
   transferring from the Lithium atom to the Oxygen
   atom
3. You can see that the Oxygen atom still does not
   have a complete outer shell. Clearly another
   Lithium atom is required to complete the compound.

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Lithium Oxide continued
Using Lewis StructuresIonic bonding between
Lithium and Oxygen

• The Lithium atoms, having lost one electron each
  have a charge of 1.
• The Oxygen atom, having gained two electrons, has
  a charge of -2.
• The final Lewis structure is illustrated here.
• The compound is Li2O.

Gizmo Demo
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Illustrate the bonding between Aluminum and
Oxygen. (Note the ratio here is a little harder
to find.)

• Draw the Lewis Structures of the individual
  atoms.
• Use arrows to show the transfer of electrons.
• Aluminum has one electron left, we need another
  oxygen atom.
• The oxygen atom now needs more electrons so we
  need another aluminum atom.
• The extra electrons on the Aluminum mean we need
  another Oxygen.
• Since, we have been able to make both atoms
  stable, we have hit the correct ratio.

Gizmo Demo
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Aluminum Oxide Continued
Aluminum and Oxygen

• Having lost 3 electrons, the aluminum has a
  charge of 3.
• Having gained 2 electrons, the oxygen has a
  charge of -2.
• Now draw the final Lewis Structure.
• This structure is designed to illustrate the
  transfer of electrons while bonding.

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Naming Ionic Compounds
Naming Ionic Compounds

• Write the name of the metal
• Write the name of the non-metal changing the end
  of the non metal name to ide.
• Examples Sodium Chloride, Calcium Oxide

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Writing the formulas for Ionic Compounds
Writing the Chemical Formula

• The trick to finding the ratio of atoms in the
  molecule.
• The easiest way is to find the number of BONDS
  the ion will make is to again refer to your
  period table as we did last day

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Writing the formulas for Ionic Compounds
Writing the Chemical Formula

1. Number the groups 1-3 going from left to right
   (skip the Transition Metals)
2. Number the groups 1-3 going from right to left
   (skip the Nobel Gases)

1
2
3
2
1
3
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Writing the formulas for Ionic Compounds
Writing the Chemical Formula

• Those numbers represent the charge the ion will
  have
• It also tells us the number of bonds it will make

1
-3
-2
-1
2
3
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Then
The Criss-Cross Rule

• Write out the atoms with their stable charge
• Al3O-2
• Cross over the numbers to the opposite atom and
  remove the sign This is the Criss-Cross Rule
• Al2O3
• If possible reduce to lowest terms.

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Example Aluminum Chloride
The Criss-Cross Rule
Step 1 Aluminum Chloride
write out name with space
Step 2 Al3 Cl-1
write symbols valence number
Step 3 Al Cl
1
3
criss-cross valence number as subscripts
Step 4
AlCl
3
combine as formula unit (1 is never shown) -
Reduce if possible
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Example Magnesium Oxide
The Criss-Cross Rule
Step 1 Magnesium Oxide
Step 2 Mg2 O-2
Step 3 Mg O
2
2
Step 4 Mg2O2
Step 5 MgO
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Multivalent Compounds

• These will include the transition metals
• When atoms get larger, their
  atomic structure can become more complex.
• This means that some atoms can have different
  numbers of valence electrons in different
  situations.

• For example if we look at the Lewis structure of
  Copper. It can have one valence electron or two
  valence electrons.
• Clearly, this atom can form more than one type of
  molecule.

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Naming Multivalent Ions

• We need to distinguish between the two or three
  different ion forms
• Use roman numerals from I VII which
  corresponds to 1 ? 7 ion charges
• For example
• Nickel can have two ion forms, Ni2 and Ni3
• These are named nickel (II) and Nickel (III)

Metal Ion charge Roman Numeral 1 I 2 II
3 III 4 IV 5 V 6 VI 7 VII
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Multivalent Compounds
Naming Multivalent Compounds

• In terms of naming these compounds, we need a
  method of distinguishing,
• CuO and Cu2O
• You need to put a roman numeral to indicate the
  charge in brackets in between the metal and non
  metal.
• Remember it is the original charge
• The roman numeral is only included if the metal
  is one of the atoms that can exhibit more than
  one charge.
• This information will be provided!

• e.g. Try to write the name for the following
  compounds without looking at the next slide
• CuF
• PbI2
• CaF2

Copper (I) Fluoride
Lead (II) Iodide
Calcium Fluoride
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How do we know which roman numeral is being used?
Naming Multivalent Compounds

• 1) CuF
• Do the reverse of the criss cross method
• Take the subscript and use it as the charge on
  the opposite symbol
• Put the charge for the metal in brackets
• ? Copper (I) Flouride
• 2) PbI2
• ? Lead (II) Iodide

Cu 1 F-1
Cu 1 F1
Pb 2 I-1
Pb 1 I2
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• Silver (Ag) always has a charge of 1
• Zinc (Zn) always has a charge of 2
• Be careful when you are asked to determine the
  roman numeral given the formula (e.g. CuS)
• This would lead you to answer Copper (I) Sulfide
• However we ALWAYS NEED TO CHECK THAT THE CHARGE
  ON THE ANION IS CORRECT
• In this case it would be -1 however, if we look
  at the periodic table we know that S is -2
• Therefore we need to multiply both charges by 2
• Copper (II) Sulfide
• MAKE SURE YOU CHECK THAT THE CHARGE ON THE
  NON-METAL IS CORRECT!!

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Ionic Compounds
Properties of Ionic Compounds

• Many ionic compounds are soluble in water.
• When they dissolve, they separate into ions.
• Water molecules surround each ion preventing it
  them from rejoining

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Properties of Ionic Compounds

• They are hard, brittle solids with high melting
  points
• Many are also electrolytes which means they
  conduct electricity when dissolved in water
• Pure water is a poor conductor of electricity,
  dissolved ions improve this property considerably