Chemical Formulas

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Chemical Formulas

• Writing Binary Compounds
• Tim Bass

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Chemical Formulas

• A shorthand method of representing the makeup of
  chemicals using chemical symbols and oxidation
  numbers.
• Positive Ions always go 1st in the formula.
• Negative Ions always go last.
• Ionic Bonded chemical formulas are always written
  as empirical formulas.
• Empirical Formula The smallest whole number
  ratio of elements in a compound.

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Golden Rule For Formulas

• The sum of the oxidation s zero!!
• Mg2 Cl-1
• K1 O-2

Sum of the oxidation numbers always equal zero!!!!
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Charged Particles

• Ion a particle with an electrical charge.
• Cation a positively charged ion.
• Anion a negatively charged ion.
• Cation always goes 1st in the formula.
• Anion always goes last in the formula.

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Oxidation Number

• Oxidation Number The apparent charge on an
  atom.
• The charge on an ion.
• Also called the valence.
• Example Ca2 Cl-1

Calcium 20P 20N 18 e-
Chlorine 17p 18N 18e-
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Noble Gas

• The greater the stability the less active a
  substance becomes.
• The noble gasses are the least active substances
  (therefore are very stable and low energy).
• When the outer shells of an element are full the
  atom is at a much lower energy level.

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Shorthand Notation

• 10Ne 1s2 2s2 2p6
• (8 valence electrons)
• 18Ar 1s2 2s2 2p6 3s2 3p6
• (8 valence electrons)
• 36Kr 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6
• (8 valence electrons)
• All noble gases (except He) have 8 valence
  electrons.

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Noble Gas (Octet) Law

• Noble Gas Law When forming compounds, elements
  tend to gain or lose electrons until they have an
  electron configuration similar to one of the
  noble gases.
• Metals tend to lose electrons (become cations)
• Nonmetals tend to gain electrons (become anions)

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Metals and Nonmetals
Nonmetals
Metals
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Oxidation Examples

• Na Cl -? Na1Cl-1
• Mg Cl ? Mg2Cl-1
• Al Cl ? Al3Cl-1

Mg 2Cl ? Mg2Cl2-1
Al 3Cl ? Al3Cl3-1
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Oxidation Numbers

• The sum of the oxidation numbers in a chemical
  formula must equal zero.
• This is the golden rule of writing formulas for
  inorganic compounds!
• There is only one category that does not follow
  this rule. They follow the rule also, but the
  rules change a little to apply to them.
• Nonmetals bonded to nonmetals
• .

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Subscripts

• Subscript Small numbers to the
  lower right of a symbol.
• Represent the number of atoms of that element in
  the compound.
• Affects only the element immediately in front of
  the subscript.
• Coefficient Large number in front of a chemical
  formula.
• Affects everything following the coefficient.

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H2O

• Hydrogen
• Oxidation X Subscript
• 1 X 2 2
• Oxygen
• Oxidation X Subscript
• - 2 X 1 - 2
• Sum of oxidation numbers 0
• ( 2 ) ( - 2 ) 0

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A Shortcut
M a k e t h e o x i d a t i o n o f o n
e e l e m e n t t h e s u b s c r i p t o
f t h e o t h e r e l e m e n t .
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A Shortcut

• There is one problem!
• These subscripts will reduce.
• Remember Ionic bonded compounds are always
  written as an empirical formula.

2 - 2
C a 2 O 2
C a O
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Polyatomic Ion

• An ion made up of more than one atom that
  behaves like one atom.

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Polyatomic Ion

• Never change subscripts within a polyatomic ion.
  (Changes the polyatomic ion.)
• If more than one polyatomic ion is needed, put
  parenthesis around the ion and add the subscript
  needed outside the parenthesis.
• NH4OH Ammonium Hydroxide
• (NH4)2O Ammonium Oxide
• Al(MnO4)3 Aluminum Permanganate

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Polyatomic Ion

• The sum of the oxidation numbers in an ion is
  equal to the charge on the ion.
• You must learn the names, formulas, and charges
  of the most common ions.
• MnO4-1 Permanganate
• OH-1 Hydroxide
• CN-1 Cyanide
• NH41 Ammonium

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Warnings

1. Once the sum of the oxidation s 0, do not
   change the formula.
2. Parenthesis are only for polyatomic ions, and
   only if they are needed two times or more in a
   chemical formula.
3. Always make sure that the final chemical formula
   is an empirical formula!

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Chemical Formulas

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