Name Chemical Compounds
Naming basic chemical compounds is essential to succeed in chemistry. Follow this guide for some basic rules on how chemical compounds get their name, and how to apply names to compounds you are unfamiliar with.
Contents
Steps
Naming Ionic Compounds
- Know what makes a compound ionic. Ionic compounds contain a metal and a nonmetal. Refer to the periodic table of elements to see what categories the elements in the compound belong to.
- Build the name. For a two element ionic compound, the naming is simple. The first part of the name is the name of the metal element. The second part is the name of the nonmetal element, with the suffix “-ide.”
- Example: Al2O3. Al2 = Aluminium; O3 = Oxygen. So the name would be “aluminium oxide.”
- Recognize transition metals. Metals in the D and F blocks of the periodic table are known as transition metals. Their charge is written with a Roman numeral when writing out the compound name. This is because they can have more than one charge and make more than one compound.
- Example: FeCl2 and FeCl3. Fe = Iron; Cl2 = Chloride -2; Cl3 = Chloride -3. The names would be iron(II) chloride and iron(III) chloride.
Naming Polyatomic Compounds
- Understand what a polyatomic compound is. These compounds are built off of groups of atoms that are bonded together, and the entire group has a positive or negative charge. You can do three basic things to polyatomic compounds:
- Add a hydrogen to the beginning of the compound. The word “hydrogen” is added to the beginning of the compound name. This reduces the negative charge by one. For example, “carbonate” CO32- becomes “hydrogen carbonate” HCO3-.
- Remove an oxygen from the compound. The charge stays the same and the ending of the compound changes from “-ate” to “–ite”. For example: NO3 to NO2 goes from “nitrate” to “nitrite.”
- Replace the central atom with another from the same periodic group. For example, sulfate SO42- can become Selenate SeO42-.
- Memorize the most common ion groups. These are the basis for forming most polyatomic compounds. Listed in order of increasing negative charge, they are:
- Hydroxide ion: OH-
- Nitrate ion: NO3-
- Hydrogen carbonate ion: HCO3-
- Permanganate ion: MnO4-
- Carbonate ion: CO32-
- Chromate ion: CrO42-
- Dichromate ion: Cr2O72-
- Sulfate ion: SO42-
- Sulphite ion: SO32-
- Thiosulfate ion: S2O3<2-</sup>
- Phosphate ion: PO43-
- Ammonium ion: NH4+
- Build compound names based off the list. Associate whatever element(s) is attached to the group ion and name accordingly. If the element comes in front of the ion group, the name of the element is simply added to the beginning of the compound name.
- Example: KMnO4. You should recognize the MnO4- ion as permanganate. K is potassium, so the compound is named potassium permanganate.
- Example: NaOH. You should recognize the OH- ion as hydroxide. Na is sodium, so the compound is named sodium hydroxide.
Naming Covalent Compounds
- Understand a covalent compound. Covalent compounds are formed by two or more nonmetal elements. The name for the compound is based off how many atoms are present. The prefix attached is the Latin term for the number of molecules.
- Learn the prefixes. Memorize the prefixes for up to 10 atoms:
- 1 atom – “Mono-“
- 2 atoms – “Di-“
- 3 atoms – “Tri-“
- 4 atoms – “Tetra-“
- 5 atoms – “Penta-“
- 6 atoms – “Hexa-“
- 7 atoms – “Hepta-“
- 8 atoms – “Octa-“
- 9 atoms – “Nona-“
- 10 atoms – “Deca-“
- Name the compounds. Using the correct prefixes, name the new compound. You attach prefixes to any part of the compound that has multiple atoms.
- Example: CO would be carbon monoxide and CO2 would be carbon dioxide.
- Example: N2S3 would be Dinitrogen trisulfide.
- In most cases, the “mono-“ prefix can be omitted, because it is implied when it is not present. It is still used for carbon monoxide due to the term being in use since early chemistry.
Tips
- Also it is very important to realize that this doesn't apply to organic chemistry.
- These rules are designed for people starting off in chemistry and science. Different rules apply when you reach advanced chemistry, for examples the rules of variable valency.
- Of course, these rules all have many exceptions, for example, despite having a 2 at the end, CaCl2 is still simply called calcium chloride, NOT calcium dichloride as might be expected. (Calcium Chloride is an ionic compound so covalent prefixes are not used)
