In chloroformaCHCL3,
(a) Assign an oxidation state to each atom in the molecule. (Hint: Draw a dot diagram first.) (b) How many electrons does the
atom own by oxidation-state electron bookkeeping? (c) How many more or fewer valence electrons are assigned to the
atom here than are present in a free
atom? (d) Is it correct or incorrect to say that the
atom in CHCL3
has a complete octet of valence electrons? Explain
The Correct Answer and Explanation is:
) Assigning Oxidation States to Each Atom in CHCl₃:
- Carbon (C): In CHCl₃, carbon is bonded to three chlorine atoms and one hydrogen atom. The oxidation state of hydrogen is +1, and the oxidation state of chlorine is -1. For carbon to balance out the oxidation states of the atoms around it, it must have an oxidation state of +4.
- Hydrogen (H): Hydrogen in CHCl₃ is bonded to carbon. Hydrogen always has an oxidation state of +1.
- Chlorine (Cl): Each chlorine atom in CHCl₃ is bonded to carbon. Chlorine, being a halogen, typically has an oxidation state of -1.
Thus, the oxidation states are as follows:
- Carbon (C): +4
- Hydrogen (H): +1
- Chlorine (Cl): -1 (for each chlorine atom)
(b) Oxidation-State Electron Bookkeeping:
The oxidation state electron bookkeeping method involves counting the electrons assigned to each atom based on its oxidation state:
- Carbon (C) in the +4 oxidation state has 4 electrons assigned to it.
- Hydrogen (H) in the +1 oxidation state has 1 electron assigned to it.
- Chlorine (Cl) in the -1 oxidation state has 7 electrons assigned to each chlorine atom (since chlorine normally has 7 valence electrons and the oxidation state of -1 means it “gains” one electron).
(c) Comparison with Free Atom Electrons:
- Carbon (C): A neutral carbon atom has 4 valence electrons (since it’s in group 14). In CHCl₃, carbon has an oxidation state of +4, meaning it has lost all of its valence electrons. This results in 4 fewer valence electrons than in a free carbon atom.
- Hydrogen (H): A neutral hydrogen atom has 1 valence electron. In CHCl₃, hydrogen also has 1 valence electron, so there are no differences.
- Chlorine (Cl): A neutral chlorine atom has 7 valence electrons. In CHCl₃, chlorine has an oxidation state of -1, meaning it has gained 1 electron. Therefore, each chlorine atom has 1 more electron than it would as a free atom.
(d) Complete Octet of Valence Electrons:
The concept of a “complete octet” means that an atom has 8 electrons in its valence shell, which is the most stable configuration. In CHCl₃:
- Carbon: It has 4 valence electrons and is bonded to 4 atoms (one hydrogen and three chlorine atoms). Carbon does not have a complete octet; it is one electron short of 8.
- Hydrogen: It has only 1 valence electron and forms a single bond with carbon. Hydrogen can only hold a maximum of 2 electrons in its valence shell, so it has a complete duet, but not a complete octet.
- Chlorine: Each chlorine atom has 8 valence electrons (7 from its own and 1 from the bond with carbon), so each chlorine atom does have a complete octet.
In conclusion, while the chlorine atoms have complete octets, the carbon atom does not have a complete octet. Therefore, it is incorrect to say that the atom in CHCl₃ has a complete octet of valence electrons.
