SO 3 has three oxygen atoms in it, so it is a different compound with different chemical and physical properties.
The system of chemical nomenclature is designed to give this compound its own unique name. Its name, if you go through all the steps, is sulfur trioxide. Different compounds have different names. In some cases, when a prefix ends in a or o and the element name begins with o we drop the a or o on the prefix.
So we see monoxide or pentoxide rather than monooxide or pentaoxide in molecule names. One great thing about this system is that it works both ways.
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From the name of a compound, you should be able to determine its molecular formula. Simply list the element symbols, with a numerical subscript if there is more than one atom of that element, in the order of the name we do not use a subscript 1 if there is only one atom of the element present; 1 is implied.
From the name nitrogen trichloride , you should be able to get NCl 3 as the formula for this molecule. From the name diphosphorus pentoxide , you should be able to get the formula P 2 O 5 note the numerical prefix on the first element, indicating there is more than one atom of phosphorus in the formula.
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Some simple molecules have common names that we use as part of the formal system of chemical nomenclature. For example, H 2 O is given the name water , not dihydrogen monoxide. NH 3 is called ammonia , while CH 4 is called methane. We will occasionally see other molecules that have common names; we will point them out as they occur.
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Which of these formulas represent molecules? State how many atoms are in each molecule. What is the difference between H 2 O and H 2 O 2 hydrogen peroxide? Why is sulfur not considered a diatomic element? What is the stem of fluorine used in molecule names? CF 4 is one example. What is the stem of selenium used in molecule names? SiSe 2 is an example. CO is a compound of carbon and oxygen; Co is the element cobalt. Previous Section. Table of Contents. Next Section. Name simple molecules based on their formulas.
Determine a formula of a molecule based on its name. Example 3 Name each molecule. A compound with one carbon atom and one oxygen atom is properly called carbon monoxide, not carbon monooxide. There are two atoms of each element, selenium and bromine. According to the rules, the proper name here is diselenium dibromide. Test Yourself Name each molecule. SF 4 P 2 S 5 Answers sulfur tetrafluoride diphosphorus pentasulfide.
Example 4 Give the formula for each molecule. The name silicon dioxide implies one silicon atom and two oxygen atoms, so the formula is SiO 2.
Compounds Containing Polyatomic Ions
We have a name that has numerical prefixes on both elements. Tri- means three, and tetra- means four, so the formula of this compound is Si 3 N 4. Test Yourself Give the formula for each molecule.
Key Takeaways Molecules are groups of atoms that behave as a single unit. Some elements exist as molecules: hydrogen, oxygen, sulfur, and so forth.
Molecules and Chemical Nomenclature
There are rules that can express a unique name for any given molecule, and a unique formula for any given name. Exercises Which of these formulas represent molecules? All Journals. New Titles. Pick and Choose. Literature Updates. For Members. For Librarians. RSS Feeds. Chemistry World. Education in Chemistry.
OPSIN: Open Parser for Systematic IUPAC nomenclature