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Published byElinor Chapman Modified over 9 years ago
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Formulas of Molecular Compounds Many compounds- made up of molecules and not ions Compound made u p of molecules are molecular compounds Use molecular formulas to write formulas of m.c. note- the molecular formula may be its empirical formula Example is CO 2
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UNLIKE IONIC COMPOUNDS, THERE IS NO SIMPLE WAY TO PREDICT AND WRITE FORMULAS FOR MOLECULAR COMPOUNDS!!! The same elements can form a number of different compounds, which have different formulas Nitrogen and Oxygen can form 5 different compounds 1. N 2 O - dinitrogen monoxide 2. NO- nitrogen monoxide 3. N 2 O 3 - dinitrogen trioxide 4. NO 2 - nitrogen dioxide 5. N 2 O 5 - dinitrogen pentoxide
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IN MOLECULAR COMPOUNDS- ELECTRONS ARE SHARED BY TWO ATOMS NOT TRANSFERRED FROM ONE ATOM TO ANOTHER In some molecular compounds - electrons are not shared equally Oxidation Number-
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Oxygen: N 2 O- Other examples NO N 2 O 3 NO 2 N 2 O 5
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Sample problem: The compound with a formula of P 2 O 3 is composed of 2 non metals- phosphorus and oxygen. What is the apparent charge on a phosphorus atom in this compound. Oxygen has 2- per atom and there are 3 oxygen atoms so there is a total negative charge of 6-. Take 6 and divide by number of P atoms (2 in this case) and you get 3. So P has an apparent charge of 3+
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Naming Molecular Compounds In naming binary molecular compounds, element with the apparent positive charge comes first. A system prefixes is used to distinguish between compounds. Prefixes are: 1. Mono- 4. Tetra 2. Di 5. Penta 3. Tri
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The stock system can also be used to name molecular compounds. The roman numeral is used to show the apparent charge in the atom with the positive oxidation number. Example- PbO 2 traditional name is lead dioxide. Stock system name is lead(IV) oxide.
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Using the Stock system to name a molecular compound N 2 O - dinitrogen monoxide What is the name of this compound in the stock system? Nitrogen (I) oxide
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Sample problem: Name the compound with the formula P 2 O 3 using both the traditional and stock system Answer- Traditional - Diphosphorus trioxide. Stock system- phosphorus (III) oxide.
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