Chem Problem Set 7 1. Write Lewis structures for each of the following molecules:
Incorrect Structure Correct Structure are two hydrogen atoms and one oxygen atom. The Lewis structure of each of these atoms would be as follows: One good example is the water molecule.
Water has the chemical formula of H2O, which means there We can now see that we have eight valence electrons six from oxygen and one from each hydrogen. With few exceptions, hydrogen atoms are always placed on the outside of the molecule, and in this case the central atom would be oxygen.
Each of the two unpaired electrons of the oxygen atom will form a bond with one of the unpaired electrons of the hydrogen atoms. The bonds formed by the shared electron pairs can be represented by either two closely places dots between two element symbols or more commonly by a straight line between element symbols: Let us try another one.
Write the Lewis structure for methane CH4.
Hydrogen atoms are always placed on the outside of the molecule, so carbon should be the central atom. Each hydrogen atom will be bonded to the carbon atom, using two electrons. The four bonds represent the eight valence electrons with all octets satisfied, so your structure is complete.
Write the Lewis structure for carbon dioxide CO2. Carbon is the lesser electronegative atom and should be the central atom. Each oxygen atom has two unshared electrons that can be used to form a bond with two unshared electrons of the carbon atom, forming a double bond between the two atoms.
The remaining eight electrons will be place on the oxygen atoms, with two lone pairs on each. Lewis Structures of Polyatomic Ions Building the Lewis Structure for a polyatomic ion can be done in the same way as with other simple molecules, but we have to consider that we will need to adjust the total number of electrons for the charge on the polyatomic ion.
If the ion has a negative charge, the number of electrons that is equal to the charge on the ion should be added to the total number of valence electrons. If the ion has a positive charge, the number of electrons that is equal to the charge should be subtracted from the total number of valence electrons.
After writing the structure, the entire structure should then be placed in brackets with the charge on the outside of the brackets at the upper right corner.
Hydrogen atoms are always placed on the outside of the molecule, so nitrogen should be the central atom.
Each hydrogen atom will be bonded to the nitrogen atom, using two electrons. Do not forget your brackets and to put your charge on the outside of the brackets Example: Write the Lewis structure for the hydroxide ion OH.
Since there are only two atoms, we can begin with just a bond between the two atoms. The charge of -1 indicates an extra electron, bringing the total electron count to 8.
Oxygen will be bonded to the hydrogen, using two electrons. Place the remaining six electrons as three lone pairs on the oxygen atom.
All octets are satisfied, so your structure is complete. Do not forget your brackets and to put your charge on the outside of the brackets Lewis Structures for Resonance Structures The existence of some molecules often involves two or more structures that are equivalent.
Resonance can be shown using Lewis structures to represent the multiple forms that a molecule can exist. The molecule is not switching between these forms, but is rather an average of the multiple forms.
This can be seen when multiple atoms of the same type surround the central atom.Write the Lewis structure of the molecule or polyatomic ion. Each of the bonds is polar, but the molecule as a whole is nonpolar. Molecular Structure and Polarity by Rice University is licensed under a Creative Commons Attribution International License.
Jul 28, · You'll need to form a double bond between the Carbon and the Oxygen atoms in order to complete their octets while still only using the 24 valence electrons available in . Example: Write the Lewis structure for the ammonium ion (NH 4 +).
Answer: Hydrogen atoms are always placed on the outside of the molecule, so nitrogen should be the central atom. After counting the valence electrons, we have a total of 9 [5 from nitrogen + 4(1 from each hydrogen)] = 9.
A Lewis structure is a graphic representation of the electron distribution around atoms. The reason for learning to draw Lewis structures is to predict the number and type of bonds that may be formed around an atom.
A Lewis structure also helps to make a prediction about the geometry of a molecule. Which Lewis structure below correctly represents the compound formed between magnesium and sulfur?
Mg+2 [: S..⋅⋅:]−2 Choose the correct Lewis structure for each molecule or ion. The Lewis structure for Helium is He with two dots next to each other, above the He symbol. The dots must be drawn next to each other, they represent the two electrons found i n the 1s-orbital.