Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: TechOutsider on January 16, 2011, 06:19:38 PM
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Ouch. Attached is a quiz on ionic naming conventions that I failed. I read the book, took copious notes on various Internet resources. Yet I still failed.
Can someone here help guide me in the right direction to master naming ionic compounds? So far, I think I need to correct the following errors:
1) Hydrogen always goes first in an acid formula (thus HF and HClO4)
2) Prefixes prefixes prefixes - e.g. H2CO3 is dihydrogen carbonate
Anything else? Not asking anyone to fix my answers, just a cursory glance and hints at avoiding future mistakes :D.
Thanks in advance :).
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fi338.photobucket.com%2Falbums%2Fn410%2Fstone_cold_05%2FIonic.jpg&hash=a043938573e9242dc113ea6a7484bb5a3b2ee275)
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Flash cards are very helpful. The amount of them may seem intimidating at first but you'll cut through them very quicky when you master them.
Other tips;
- If hydrogen is out in front (HCl, HBrO, HNO3 etc.) it's most likely an acid. You had some formulas correct however the hydrogen was not out in front.
- It's generally safe to assume halogens will form a single bond; hydrofluoric acid could not be FH4 if you remember this and the previous tip.
- Make the halogen acid nomeclature chart;
1) Hypo-*-ous
2) *-ous
3) *-ic
4) Per-*-ic
Make twelve boxes with the top title labeled Cl, Br, I and the side as I labeled 1-4 with pre/suffixes. Fluorine has hydrofluoric (HF) and hypofluorous (HFO) with no analogues to bromous (HBrO2), bromic (HBrO3), and perbromic (HBrO4) forms.
- Metal and non-metal combination is usually ionic, so PbI2 is ionic thus "lead iodide (http://en.wikipedia.org/wiki/Iodide)" not "lead iodine (http://en.wikipedia.org/wiki/Iodine)".
- CrO4 is chromate ion not chromium. I'd recommend flash cards to help you remember anions/cations.
- Avoid ambiguity to get full credit. For example "copper chloride" could be Copper(II) chloride/Cupric chloride or Copper(I) chloride/Cuprous chloride. This is not necessary for metals that have one oxidation state (Group 1, Group 2, Zinc, etc.)
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I'm not sure it always work but usually in ionic compounds, cations are written first.
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This is really testing two classes of compounds, ionic compounds and acids. For ionic compounds, the naming convention is cation + anion, in that order. The cation is generally just the name of the element, but the anion can be more complex. If it is monatomic, it should end in -ide (eg bromide rather than bromine, nitride rather than nitrogen, oxide rather than oxygen). For polyatomic ions, it is useful to memorize the important ones, and then look for patterns. You will never have an anion that is named the same as the element (eg sodium chlorine).
For acids with monatomic "anions", the naming convention is hydro___ acid. HBr is hydrobromic, and HF is hydrofluoric, for example. Some very weak acids are named as ionic compounds rather than acids; H2S is named hydrogen sulfide rather than hydrosulfuric acid. For acids with polyatomic "anions" Fluorine's rules are very helpful.
Don't worry about prefixes in front of cations. When we are talking about ionic compounds, they do not matter. Na2O is not disodium oxide, but just sodium oxide. Also, remember that the overall molecule has to be neutral, meaning the positive cations and the negative anions have to cancel out. For some polyatomic anions, the charge has to be memorized. With a lot of practice and increased chemical intuition, you will learn to deduce this. I would really go back and read your book and notes more. Some of the mistakes you've made are indicative of lack of understanding of the chemistry behind ionic compounds and acids. Rules for nomenclature are important, but so is understanding the chemistry. An example would be HF4, which is clearly not possible because hydrogen cannot bond to 4 things.
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Thanks guys for the help. I think I'll have it down by the next assessment! Wish me luck :).
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a further hint may include:
the names of the 'anion' (also called radicals) in ionic compounds change depending on number of oxygen.
as a general rule, the greate the number of oxygen, the name ends in ate e.g sulfate SO42-.
if the anion contains a lesser number of oxygen, the name ends in ite e.g sulfite SO32-.
if the anion does not contain oxygen, the name ends in ide,e.g sulfite sulfide S2-
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the names of the 'anion' (also called radicals) in ionic compounds change depending on number of oxygen.
a radical and an anion are not necessarily the same.
if the anion does not contain oxygen, the name ends in ide,e.g sulfite S2-
typo: sulfide you meant of course
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true. thanks for clarification and typo.