Naming Chemical Compounds

Chemistry is broken.

We can see this illustrated in the statement "There is not just one universally accepted system used to name all compounds".

However the most common system is defined by IUPAC (which still takes exceptions. Because that's the way to do things. 100%).

Common Binary Compounds

Some compounds with hydrogen are known by their common names:

  • NH3 = Ammonia
  • NH4 = Ammonium
  • H2O = Water
  • CH4 = Methane
  • AsH3 = Arsine
  • PH3 = Phosphine
  • SiH4 = Silane

Binary Compounds Between Non-Metals

Named with prefixes:

  • Mono-
  • Di-
  • Tri-
  • Tetra-
  • Penta-
  • Hexa-

Examples

  • CO = Carbon Monoxide
  • SO2 = Sulfur Dioxide
  • PCl5 = Phosphorus Pentachloride

Polyatomic Ions

Compounds with Polyatomic Ions (multiple ions) are named for the first element, followed by the next group. There doesn't need to be a prefix because they are combined to be neutral, and hence can be calculated.

Examples

  • Ca(OH)2 = Calcium Hydroxide
    • Ca2+ + OH- -> OH needs to have 2 to match the 2+ and balance out to 0
  • H2O2 = Hydrogen Peroxide
    • H+ + O22- -> H needs to have 2 to match the 2- and balance out to 0

Ambiguous Compounds

If two (or more) elements can combine in multiple ways then we need to distinguish between them.

Prefix System

We can add prefixes to the elements to indicate the combination ratio, as we did above with binary compounds.

Examples

  • N2O3 = dinitrogen trioxide
  • Fe3O4 = tri-iron tetraoxide

Modern Roman Numerals System

Apparently the (sensible) above system is being superseded by the (moronic) Roman Numeral System.

Compounds are written with the elements/molecule groups from left to write. After each element, if it is ambiguous what oxidation state (charge) it is in (because there could be multiple compounds), we add the state in roman numerals.

Of course, there are exceptions to every rule. However the general case for determining the symbol from the word is:

Calculating State: Formulae to Name

  • Take the second element's charge, and its ratio.
  • Multiply these together.
  • Divide this number by the ratio of the first element.
  • This is the oxidation state of the first element.

Calculating State: Name to Formulae

  • Take the oxidation state of the first element.
  • Take the charge of the second element.
  • Multiply them together = x.
  • Divide this number (x) by the oxidation state. This is the ratio of the first element.
  • Divide x by the charge. This is the ratio of the second element.

Examples

  • NO = Nitrogen (II) Oxide
    • Second element = 2+, Ratio = 1
    • 2/1 = 2
    • Therefore oxidation state = 2
  • NO2 = Nitrogen (IV) Oxide
    • Second element = 2+, Ratio = 2
    • 4/1 = 4
    • Therefore oxidation state =4
  • Phosphorus(III) Chloride = PCl3
    • x = 3 * 1
    • 3/3 = 1 = first ratio
    • 3/1 = 3 = second ratio

Oxyanions

Oxygen forms polyatomic ions (anions, in this case) with all other non-metals (except fluorine, apparently) and with some metals (e.g. manganese, chromium = special for some reason).

Oxygen & 2nd Row Elements

  • Boron, Carbon and Nitrogen can form oxyanions
  • Only 3 oxygen atoms can fit
  • Therefore XO, XO2 and XO3 (where X is B, C or N)
  • Only negatively charged combinations are oxyanions - Hence CO2 is not an oxyanion, as it is balanced.

Oxygen & 3rd+ Row Elements

  • Only 4 oxygen atoms can fit around the central atom

Naming Conventions

  • x = max number of oxygen atoms
  • element + x = element_stem-ate
  • element + (x-1) = element_stem-ite

Charge/Oxidation State

  • Group 14 defaults to -2
  • Group 15 defaults to -3, except for nitrite and nitrate
  • Group 16 defaults to -2
  • Group 17 defaults to -1

Per and Hypo Prefixes

To allow for systematic differentiation, some elements use per- and hyp- to indicate how many oxygen atoms there are. This system appears to only be standardised for Halogens, but does exist for compounds such as SO5 (out of course, I believe).

Halogens

  • Hypo-element-ite = XO
  • -element-ite = XO2
  • -element-ate = XO3
  • Per-element-ate = XO4

Examples

  • PO33- = Phosphite
  • NO2- = Nitrite
  • Nitride = N3-
  • Phosphate = PO43-
  • CaSO3 = Calcium Sulfite
  • Silver(II) Carbonate = Ag2CO3
  • Lead (II) Nitrate = Pb(NO2)2
  • (NH4)2CO3 = Ammonium Carbonate
  • IO- = Hypoiodite
  • Periodate = IO4-
  • Magnesium Perchlorate = Mg(ClO4)2

Hydrogen Acids

When oxyanion + hydrogen -> neutral compound is dissolved in water it forms an acidic solution. It's called protonated

Changes

  • -ite -> -ous
  • -ate -> -ic
  • "acid" is added on the end

Examples

  • Nitrous Acid = HNO2
  • Bromous Acid = HBrO3
  • HIO4 = Periodic Acid
  • H2SiO3 = Silicic Acid
  • H3BO3 = Bromic Acid
  • Chloric Acid = HClO3

Binary Acids

Hydrogen + One element are called hydroelement-acids when dissolved in water.

Examples

  • Hydrofluoric Acid = HF (Hydro = No oxygen. Hence just HF).
  • HI = Hydroiodic Acid
  • H2S = Hydrosulfuric Acid

Metallic Oxyanions

Most common metal oxyanions:

  • Permanganate Ion = MnO4
  • Chromate = CrO4
  • Dichromate = Cr2O7

Calculating Oxidation State of the Metal

Oxygen is always 2-. Using this we can calculate either the other oxidation state, or the oxyanion oxidation state, using a simple formula:

  • a = Element oxidation state * ratio of element
  • b = -2 * ratio of oxygen
  • overall oxyanion oxidation state
  • a + b = c

Example

  • CrO42-
  • c = 2-
  • b = -2 * 4 = -8
  • therefore a = -8 —2 = 6
  • therefore a = 6
  • therefore Chromium is +6 in Chromate

Polyprotic Acids -> Polyatomic Anions

When one or two protons are reacted with bases the anions contain hydrogen (and sometimes oxygen).

Examples

  • H+ + CO32- -> HCO3- = Hydrogencarbonate anion
  • Na2HPO4 = Sodium Hydrogenphosphate
  • Ammonium hydrogensulfate = NH4HSO4
  • Dihydrogenphosphate ion = H2PO4-

Water of Crystallisation

This is indicated in one of two ways:

  1. Prefix-hydrate
  2. Numbers-water

Examples

  • Na2SO4.10H2O = Sodium Sulfate Decahydrate
  • Na2SO4.10H2O = Sodium Sulfate-Ten-Water

Oxidation State

The number of charges an atom would have in a molecule/ion if shared electrons were transferred completely to the more electronegative atom - blackman 12.1

I.e. if in CO3 all carbon electrons that are shared would go to oxygen. So 6- goes to 2- with the +4 of Carbon.