Draw the Lewis structures for each of the following, determine the shape of the molecules.
a. H2S
b. CN3-
c. CCl4
d.NH4
e.PO4-
f.PCL3
f.SF6
and explain how do you determine the shape of it
We can't draw structures or Lewis dot structures on the board. Most of this you can find on the Internet by search on Google. For example, here is H2S.
http://www.google.com/search?q=Lewis+structure+H2S&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a
can you explain how to determine the shape of it though?
Rules and introduction that is just too long to type in manually. Here is a good site that explains it. The introductory page comes up first (What is VSEPR), then you look on the left for the remainder of the information. Look at Rules and Counting Regions of High Electron Density. From there you get the shapes.
http://www.chem.purdue.edu/gchelp/vsepr/
To draw Lewis structures, you need to follow a few steps:
Step 1: Determine the total number of valence electrons for the molecule. Valence electrons are the electrons in the outermost energy level of an atom.
Step 2: Determine the central atom. The central atom is usually the least electronegative element or the element that can form the most bonds.
Step 3: Connect the central atom to the surrounding atoms using single bonds. Place all remaining electrons around the atoms as lone pairs.
Step 4: Check if any atoms in the molecule need additional electrons to complete their octets. If so, convert lone pairs from surrounding atoms into multiple bonds (double or triple bonds) with the central atom.
Now let's apply these steps to each of the molecules you listed and determine their shapes:
a. H2S:
- Hydrogen (H) has 1 valence electron, and sulfur (S) has 6 valence electrons.
- Sulfur will be the central atom since it is less electronegative than hydrogen.
- Connect the hydrogen atoms to sulfur using single bonds, resulting in H-S-H.
- Place the remaining electrons as lone pairs around sulfur.
- Sulfur needs two additional electrons to complete its octet, so convert one lone pair to a double bond between sulfur and one of the hydrogen atoms: H-S=H.
- The shape of the molecule is bent or V-shaped due to the lone pair pushing down on the bond angles.
b. CN3-:
- Carbon (C) has 4 valence electrons, and nitrogen (N) has 5 valence electrons.
- Carbon will be the central atom.
- Connect each nitrogen atom to carbon using single bonds, resulting in C-N-N-N.
- Place the remaining electrons as lone pairs around nitrogen.
- Nitrogen atoms need two additional electrons to complete their octets, so convert two lone pairs from nitrogen atoms into double bonds with carbon.
- The shape of the molecule is trigonal planar.
c. CCl4:
- Carbon (C) has 4 valence electrons, and chlorine (Cl) has 7 valence electrons.
- Carbon will be the central atom.
- Connect each chlorine atom to carbon using a single bond, resulting in C-Cl, C-Cl, C-Cl, C-Cl.
- Place the remaining electrons as lone pairs around chlorine.
- Carbon has already used all of its available electrons, and each chlorine has an octet.
- The shape of the molecule is tetrahedral.
d. NH4+:
- Nitrogen (N) has 5 valence electrons, and hydrogen (H) has 1 valence electron.
- Nitrogen will be the central atom.
- Connect each hydrogen atom to nitrogen using a single bond, resulting in H-N-H, H-N-H, H-N-H.
- Place the remaining electrons as a lone pair on nitrogen.
- Hydrogen atoms do not need more electrons to complete their duets, but nitrogen needs one more electron to complete its octet.
- The shape of the molecule is tetrahedral.
e. PO4-:
- Phosphorus (P) has 5 valence electrons, oxygen (O) has 6 valence electrons.
- Phosphorus will be the central atom.
- Connect each oxygen atom to phosphorus using a single bond, resulting in O-P-O, O-P-O, O-P-O.
- Place the remaining electrons as lone pairs around oxygen.
- Phosphorus needs three additional electrons to complete its octet, so convert three lone pairs from oxygen atoms into double bonds with phosphorus.
- The shape of the molecule is tetrahedral.
f. PCl3:
- Phosphorus (P) has 5 valence electrons, and chlorine (Cl) has 7 valence electrons.
- Phosphorus will be the central atom.
- Connect each chlorine atom to phosphorus using a single bond, resulting in Cl-P-Cl, Cl-P-Cl, Cl-P-Cl.
- Place the remaining electrons as lone pairs around chlorine.
- Phosphorus has already used all of its available electrons, and each chlorine has an octet.
- The shape of the molecule is trigonal pyramidal.
g. SF6:
- Sulfur (S) has 6 valence electrons, and fluorine (F) has 7 valence electrons.
- Sulfur will be the central atom.
- Connect each fluorine atom to sulfur using a single bond, resulting in F-S-F, F-S-F, F-S-F, F-S-F, F-S-F, F-S-F.
- Place the remaining electrons as lone pairs around sulfur.
- Sulfur has already used all of its available electrons, and each fluorine has an octet.
- The shape of the molecule is octahedral.