Which formula represents an asymmetrical molecule?
(1) CH4
(2) CO2
(3) N2
(4) NH3
An assymetrical molecule is a molecule whose charge is distributed unevenly. A polar molecule is an asymmetrical molecule. How can we figure out if the molecule is polar?
First we need to draw the Lewis dot structures for the molecules.
For a molecule to be non polar, we need the central atom to be surrounded by identical elements and have no lone electron pairs. For example, CH4 is non polar because central atom C is surrounded by four hydrogens and also has no lone electrons. CO2, is non polar as well because central atom has no lone electrons and is surrounded by two oxygens. N2 is non polar because it contains 2 identical elements. This leaves us with NH3. According to the Lewis dot structure, while N is surrounded by the same elements (three hydrogens), it has a lone pair of electrons and therefore is a polar molecule. Therefore, choice 4 is the correct answer.
Some other examples of polar molecules are: H2O, HCl, and HF
Chemistry regents exams very often ask questions based on the same molecules. Therefore, we recommend our students to practice drawing Lewis dot structures for the molecules listed in this question as well as H2O, HCl, and HF.
Here is the list of polarities:
H2O - polar
HF, HCl, CO - polar
NH3- polar
CH4, CCl4 - nonpolar
N2, O2, Cl2 - nonpolar
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