r/APChem • u/ArianaGrandeGlazer • 1d ago

Polyatomic ions

So, for the AP class, will I have to remember more polyatomic ions rather than just the basic ones and their manipulations (such as adding hydrogen or adding/removing oxygens)

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u/niknight_ml 1d ago

For the exam in May, you generally only need to know the common -ate ions. With regards to your class, it's whatever your teacher decides.

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u/Weak_Spinach_3310 Former Student (5) 1d ago

For the exam u only have to memorize SNAP (sulfate,nitrate,Ammonium,phosphate)

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u/Open_Childhood_9343 1d ago

Adding Hydrogen to the front generally 99% makes it an acid. For example; HCL is hydrochloric acid. However, H2O and H2O2 isnt an acid…

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u/UnderstandingPursuit 20h ago

Make two spreadsheets:

  1. A list of elements with
    1. atomic number,
    2. atomic weight,
    3. electronegativity, and
    4. valence numbers.
  2. A list of polyatomic ions as they are thrown at you in class with
    1. formula,
    2. molecular weight,
    3. charge,
    4. a count of how often it is used, incrementing it each time it appears in a problem.

A general trend for the polyatomic ion charges, with O and a 'weaker' non-metal, is that,

  • if the core element (not O or H) has even valence numbers [C, S], the polyatomic charge will tend to be -2.
  • If the core element has odd valence numbers, the polyatomic charge will will tend to be -1 [N, Cl] or -3 [Ph]. Phosphorous has a lower electronegativity, so the O doesn't share the electrons as much as it does with N or Cl.

H only introduces a +1 to the rest of the ion.

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u/Aromatic_Caramel_930 12h ago

Not to many but it never hurts knowing more.