Formula Writing

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• Formula Writing

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MONatomic Ion

• An ion made up of one element.
• Example Ba2 or K1

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• The
• Rules

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First write each element symbol and oxidation
number
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Next Write the cation (metal) first, followed by
the anion (nonmetal)
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• Then use the CRISS-CROSS method the oxidation
  number of each atom is swapped and written as a
  subscript instead of a superscript

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Example Barium Bromide

• Ba2 Br-1 (apart with superscripts)
• Ba2 Br-1 (criss-cross oxidation s)
• Ba1Br2 (together w/ subscripts)
• BaBr2 ( formula the 1 is understood)

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Try Lithium Chloride

• apart with superscripts _______________
• criss-cross oxidation s ______________
• together w/ subscripts _______________
• formula the 1 is understood _________

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Polyatomic Ion

• An ion made up of more than one element

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• The individual atoms in the polyatomic ion DO NOT
  have oxidation numbers, but the ENTIRE COMPOUND
• has an oxidation
• number

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Example PO4-3

• Phosphate Ion
• A polyatomic ion with an oxidation number of -3

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The Rules

• Write the symbol and oxidation number for each
  element and polyatomic number
• Write the cation first, followed by the anion
• Use the criss-cross method the oxidation numbers
  are swapped and written as subscripts instead
  of superscripts

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• If there is more than one polyatomic ion present,
  the polyatomic ion formula is inside parentheses
  and the subscript is added outside the
  parentheses.

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NEVER CHANGE the subscript within the polyatomic
ion itself!!!!!!!!!!!!!!!!!!!!!!!!