I am trying to draw the Lewis dot structure for CH2O2. Where would I put the elements? I'm guessing carbon would be in the middle. Also, how do you know where to put each element when drawing Lewis structures in general? Like obviously if you have CH4 or something then you know that C is going in the middle and the 4 H's will go around it, but how would you know for ones with several elements? Help please! Thank you
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When I was teaching chemistry, I always told my students to follow these rules:
1) Carbon, if present, is ALWAYS in the center.
2) Hydrogen is NEVER in the center.
3) In any other case, the LEAST ELECTRONEGATIVE element goes in the center.
If you're having trouble with the last part, the least electronegative element is usually the first one written in the formula (for example, in SO2, sulfur is less electronegative than oxygen and would therefore be placed in the center). Also, the least electronegative element is located farthest left or down on the periodic table. Again, sulfur is below oxygen on the table, so we can assume that sulfur is less electronegative than oxygen.
Those rules work very well for molecules that have only one central atom, such as SO2, NH3, and PCl5, but they are less helpful for molecules that have multiple central atoms, like P4O10, CH3COOH, or C2H2Cl2. In many such molecules, the central atoms form a ring or chain (or even more complicated structures). In those cases you kind of have to play around with the atoms to figure out the optimum arrangement. It also helps to know a little bit about organic functional groups and the valences of particular atoms.
In the case of CH2O2, you're definitely going to put carbon in the center. The two oxygen atoms will most likely bond directly with the carbon atom. Carbon usually has a valence of 4, meaning it forms 4 bonds with adjacent atoms. Oxygen typically has a valence of 2. If both oxygen atoms were double-bonded to the carbon atom, that wouldn't leave any bonding locations for the two hydrogen atoms (both of which have valences of 1).
1) Carbon, if present, is ALWAYS in the center.
2) Hydrogen is NEVER in the center.
3) In any other case, the LEAST ELECTRONEGATIVE element goes in the center.
If you're having trouble with the last part, the least electronegative element is usually the first one written in the formula (for example, in SO2, sulfur is less electronegative than oxygen and would therefore be placed in the center). Also, the least electronegative element is located farthest left or down on the periodic table. Again, sulfur is below oxygen on the table, so we can assume that sulfur is less electronegative than oxygen.
Those rules work very well for molecules that have only one central atom, such as SO2, NH3, and PCl5, but they are less helpful for molecules that have multiple central atoms, like P4O10, CH3COOH, or C2H2Cl2. In many such molecules, the central atoms form a ring or chain (or even more complicated structures). In those cases you kind of have to play around with the atoms to figure out the optimum arrangement. It also helps to know a little bit about organic functional groups and the valences of particular atoms.
In the case of CH2O2, you're definitely going to put carbon in the center. The two oxygen atoms will most likely bond directly with the carbon atom. Carbon usually has a valence of 4, meaning it forms 4 bonds with adjacent atoms. Oxygen typically has a valence of 2. If both oxygen atoms were double-bonded to the carbon atom, that wouldn't leave any bonding locations for the two hydrogen atoms (both of which have valences of 1).
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