Steps to write the L ewis structure Find the number of valence electrons for each of the atoms in the molecule. The number of valence electrons is usually the same as the group number where the element is located.
The number of valence electrons for carbon is 4 (group 4)
The number of valence electrons for sulfur is 6 (group 6)
Count the total number of valence electrons in the molecule: Sum the valence electrons from each atom in the molecule
For CS 2 Total valence e. from C: 4 4 e. x 1 C = 4 Total valence e. from S: 6 6 e. x 1s = 6 Total valence e. in the molecule: 4 + 6 = 10
Use the octet rule to figure how many octet electrons the atoms should have: Most atoms need 8 electrons to complete their valence shield Hydrogen is an exception and needs only 2
For CS 2 Carbon should have 8 valence electrons Sulfur should have 8 valence electrons
Draw an initial sketch of the molecule by placing the symbol of each atom in a diagram For carbon disulfide, CS 2 S C S
Place the valence electrons of each atom around them, starting from the outer atoms
For CS 2 Sulfur has 6 valence electrons:
For CS 2 Carbon has 4 valence electrons:
Each bond in a molecule is made up from two electrons. Each atom in the molecule need to be bonded together to its nearest atom.
For CS 2
For CS 2
Bond Bond
Count the number of electrons each atom has after forming a single bond: Each s ulfur atom has 7 electrons, it needs 8
Count the number of electrons each atom has after forming a single bond: Carbon atom has 6 electrons, it needs 8
To complete the octet we would need to pair another couple of electrons for each sulfur atom
To complete the octet we would need to pair another couple of electrons for each sulfur atom
To complete the octet we would need to pair another couple of electrons for each sulfur atom
Now coun t the number of electrons around each atom: each atom should have 8 electrons
Each sulfur has 8 electrons around, its valence is complete.
Carbon has 8 electrons around, its valence is complete.
Practice writing the Lewis structure of any other molecule ! For more resources on chemistry visit: Periodic table with names http://periodictablewithnames.net