8th grade chemistry: IV. molar mass: Empirical formula
Molecules consist of two or more atoms bonded to one another through "covalent" bonds. Identification of these molecules is through their molecular formulas. There is a hierarchy of formulas: 1. Empirical formula: Consider the benzene molecule which has 6 carbon and 6 hydrogen atoms. Therefore the ratio of carbon to hydrogen atoms is 6 to 6 which we can simplify to 1 to 1 (i.e., 1:1). The empirical formula expresses this most simple ratio, i.e. C1H1 (or CH). The empirical formula expresses the most simple ratio of atoms in the molecule. Examples: methane: CH4, ethane CH3, water H2O, benzene CH, acetic acid COH2 |
Video Explanation: Difference between empirical & molecular formula, How to calculate both:
2. Molecular formulas: go one step beyond the empirical formula in that they express not only the correct ratio but the correct number of atoms in the molecule. In the case of benzene the molecular formula would be C6H6. other Examples: methane CH4, benzene C6H6, ethane C2H6, acetic acid C2O2H4, water H2O ( Notice that sometimes the empirical and molecular formulas are the same. This will happen when the molecular formula also expresses the most simple ratio of atoms.)
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3. Structural formula: The structural formula not only has the correct number of atoms but includes the bonding structure of the molecule (i.e., which atoms are bonded together).
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4. 3D Structural formula: Molecules are three dimensional (3D) objects. The 3D structural formula is an attempt to convey the 3D geometry of the molecule. dashed bonds depict atoms going in back of the plane. Note: The triangular bonds depict atoms coming out of the plane and the dashed bonds depict atoms going in back of the plane. Go Here if you would like to learn more about 3D structures
