i need help with nomenclature a.k.a naming compounds. we learned about type 1, 2, and 3 compounds and the different methods but im sooo confused can someone please explain these different types please!
Help with naming chemical compounds in chemistry?
I'll do my best! Get yourself comfortable...this is going to take a couple of minutes:
(1) Binary ionic compounds. These are compounds that are made of two simple ions. NaCl and CuBr2 are good examples.
These compounds are named in two parts: The cation (positive ion) is named first, followed by the anion (negative ion). This is the same order the formula is written in, so don't worry about having to switch it around.
(1.1) Cation nomenclature
There are two kinds of cations you might have to deal with:
(1.1.1) Metals that have only one possible oxidation state. These include metals from groups I and II as well as aluminum, zinc, silver, and a handful of less common ones. The names of these ions are the same as the element's name. For example, the Na(+) ion is just called a sodium ion. The Al(3+) ion is called an aluminum ion.
(1.1.2) Transition metals, which, in many cases, have more than one possible oxidation state. In these cases, you use a roman numeral in parentheses to indicate the charge of the cation. For example, iron can have either a +2 or +3 charge. It wouldn't do to simply refer to iron ions, since it's not clear whether we mean Fe(2+) or Fe(3+). So, we refer to Fe(2+) as iron(II) and Fe(3+) as iron(III). Another example: copper can have either a +1 or +2 oxidation state, so we can have copper(I) and copper(II) ions.
An older method of naming indicates the oxidation state of the transition metal ion by adding -ic or -ous to the Latin form of the ion's name. For example, iron's Latin name is ferrum (from which we get the symbol Fe). In the older system, Fe(3+) would be called ferric, while Fe(2+) would be called ferrous. For copper (cuprum in Latin), Cu(+) would be called cuprous, while Cu(2+) is cupric. The -ic ending is always reserved for the higher of the oxidation states. That method is confusing, however, so unless your teacher insists on it I would stick to Roman numerals.
(1.2) Anion nomenclature
Anions are named by dropping the end of the element's name and adding -ide. For example, the Cl(-) ion is called chloride. O(2-) is an oxide ion, and As(3-) is an arsenide ion. You just have to practice learning where to chop off each element's name to add the -ide.
Some examples:
FeCl3 = iron(III) choride (or ferric chloride)
Na2O = sodium oxide
Ca3P2 = calcium phosphide
CuS = cupper(II) sulfide (or cupric sulfide)
(2) Tertiary ionic compounds
Tertiary ionic compounds are ionic compounds that contain a polyatomic ion. These can be trickier to name than binary ionic compounds because you need to be able to recognize the common polyatomic ions. I recommend you learn them quickly, so this will make more sense to you.
There is only one important polyatomic cation: the ammonium ion, NH4(+). Whenever you see the ammonium ion in a compound, its name does not change. Just call it ammonium __________, where the name of the anion goes in the blank.
Polyatomic anions do not change their names when they are used in formulas. So, if NO3(-) is the nitrate ion, then KNO3 is called potassium nitrate. SO4(2-) is the sulfate ion, so Fe2(SO4)3 is iron(III) sulfate. NH4Cl would be called ammonium chloride.
(3) Acids
Acids are compounds that contain an ionizable hydrogen. In most cases, the hydrogen will be the first element written in the formula, so you're pretty safe in assuming that any formula that starts with H is an acid (even water, H2O, can be an acid when in the presence of a base). There are two main types of inorganic acids: binary acids and tertiary acids (also known as oxyacids).
(3.1) Binary acids are made of hydrogen and one other element. They always have the form hydro_____ic acid, where the blank is filled by the stem of the anion. For example, HCl is called hydrochloric acid. HBr is hydrobromic acid, and H2S is hydrosulfuric acid.
(3.2) Oxyacids are made of hydrogen and a polyatomic anion. They do NOT use the prefix hydro. If the polyatomic ion ends in -ate (such as nitrate, sulfate, carbonate, etc), then the acid's name has the form _______ic acid, where the blank is filled by the stem of the anion's name. For example, HNO3 (hydrogen nitrate) is called nitric acid. H2SO4 (hydrogen sulfate) is called sulfuric acid.
Oxyacids whose anion ends in -ite (such as nitrite or sulfite) are given names with the form _______ous acid. For example, HNO2 (hydrogen nitrite) is nitrous acid. HClO2 (hydrogen chlorite) is chlorous acid.
(4) Binary molecular compounds.
Binary molecular compounds are covalently-bound compounds with two different elements in them. Examples would be SO2, XeF4, and NI3. These compounds have two-part names. The parts of the name are in the same order as the elements are listed in the formula, which in turn is generally listed in order of increasing electronegativity (EN).
(4.1) Naming the first element.
If the subscript of the first element is an understood 1, then you wouldn't change the element's name. For example, the first part of CO2's name is just "carbon". The first part of SO3's name is just "sulfur".
If the subscript is 2 or higher, add a prefix to indicate the subscript. The prefixes are:
2 - di
3 - tri
4 - tetra
5 - penta
6 - hexa
So, if you were naming the compound P4O10, you would begin with "tetraphosphorus". The compound N2Cl4 would begin with "dinitrogen".
(4.2) The second element's name ALWAYS begins with a prefix, even if the subscript is an understood 1 (in which case the prefix is mono-). Putting it all together, SO3 becomes sulfur trioxide. CO is called carbon monoxide, while CO2 is carbon dioxide. XeF4 is xenon tetrafluoride, and N2Br4 is dinitrogen tetrabromide.
So, I hope that's complete enough, and I hope it helps. Good luck to you!
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