At some point in your life, you’ll need to know how to name compounds and write formulas.
You may know that a compound is a combination of two or more elements, while a formula is a set of mathematical equations using symbols representing elements and their quantities.
It is common for the general public to confuse the two, but they have very different uses.
A chemist will need formulas to determine the properties of a newly-synthesized chemical compound.
A linguist may need to know compounds and their names in order to correctly identify words in a sentence.
The following paragraphs will teach you the basics of naming compounds and how to write formulas.
As mentioned above, a compound is a combination of two or more elements.
Typically, elements are either basics or building blocks used to create other compounds.
Basics are very common and are usually non-metallic and acids or bases.
Examples of bases include NH3 (ammonia) and HCl (hydrogen chloride).
Non-metals are common as well and include S (sulfur), P (phosphorus), As (arsenic), and I (iodine).
A compound containing H2O (water) is also commonly known as ‘fresh water’.
The elements that a compound is made of are called the components of the compound.
Each element has a specific atomic number which determines the number of protons in the element’s nucleus.
For example, C6H12O6 (glucose) is a compound made of carbon, hydrogen, oxygen, and six units of sugar.
The carbon and hydrogen are elements, while the oxygen and sugar are building blocks (or components).
What Is A Molecular Formula?
A molecular formula, or formula, is a shorthand way of writing the composition of a chemical compound.
The molecular formula for glucose is C6H12O6 ( carbon 6 atoms (C6), hydrogen 12 atoms (H12) and oxygen 6 atoms (O6)).
It is important to note that the molecular formula does not explicitly state the number of moles ( C6H12O6 is a mass of 238.15 grams per mole or one molality of glucose), but it is the number of atoms that determine the weight of the molecular formula.
A molecular formula does not replace the structure of a compound nor does it directly represent the chemical compound, rather it is a concise way of stating the composition of the compound.
All Forms Of The Compounds Have The Same Molecular Formula
The following chart illustrates the correspondence between the various forms of a compound (hereinafter referred to as ‘x’) and their corresponding molecular formula, or formula:
- XH2O – Has a molecular formula of (H2O) (water)
- XYZ – Has a molecular formula of (XYZ) (x atoms (X) of element Y and Z atoms (Z))
- X2Y2Z2 – Has a molecular formula of (X2Y2Z2) (x atoms (X) of element Y and Z atoms (Z))
- C6H12O6 – Has a molecular formula of (C6H12O6) (carbon 6 atoms (C6) and oxygen 6 atoms (O6))
- CaC5H8O7 – Has a molecular formula of (CaC5H8O7) (calcium (Ca) and carbon 5 atoms (C5) and oxygen 7 atoms (O7))
In general, the molecular formula of a compound that contains non-metals is made of atoms from groups 1 and 2 in the periodic table.
Metals and their compounds have a molecular formula made of atoms from groups 17 and 18 in the periodic table.
Determining The Molecular Formula Of A Compound
The molecular formula of a compound can be determined using several techniques, the simplest of which is by weighing the compound.
Another method is to hydrogenate the compound, then reduce the resulting substance to the parent compound followed by oxygenate the compound to obtain the molecular formula.
Another method is to take the infrared spectrum of the compound and match it to the infrared spectrum of the parent compound or an analogous substance.
Writing Formulas For Compounds
Once you know the molecular formula of a compound, you can write the formulas for other compounds that are isomorphic to the original compound.
An isomorphic formula is a formula that can be converted directly into the formula for the original compound by using the substitution table shown below:
- R → H – (R → H) (Ra → H) (alkyl chains)
- NR2 → R – (NR2 → R) (organic radicals)
- Cl → Br – (Cl → Br) (chloro → bromo)
- F → OH – (F → OH) (fluoro → hydroxyl)
- O → S – (O → S) (oxidation)
These substitution rules apply to the formulas for both inorganic and organic compounds.
For example, CCl3F (chloro-fluorocarbene) is a compound that contains carbon, chlorine, fluorine, and carbon.
If you know that CCl3F is made of a carbene (carbon and a chlorine atom), you can use the substitution table above and convert the formula to that of CHCl3F (carbene 3-fluoropropane).
Learn The Important Phrases
Since naming compounds and writing formulas are essential to many practices in the chemical sciences, knowing the right words is very important.
These phrases may occur in lab manuals, research papers, and other technical documents.
Even if you do not plan to join the chemical sciences, it is essential to know the right words and theory behind them to have a better understanding of what is going on.
Learn The Theory
As stated above, a compound is a combination of two or more elements.
Usually, the theory that is taught in the first year of a chemistry program is a very basic version of chemical theory and does not go into great detail regarding compounds.
However, even that brief introduction to chemistry is useful in understanding the naming compounds and formulas required in everyday life.