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# Dot & cross diagram watch

1. What would the dot & cross diagram be like for CN-? I have done an OCR question on this and the structure does not include any dative covalent bond. This is the answer from the mark scheme but I don't get how carbon will be gaining that electron when the negative sign is next to N. Also I searched this up but found that this ion involves a dative covalent bond.

Help?

Thanks
2. (Original post by coconut64)
What would the dot & cross diagram be like for CN-? I have done an OCR question on this and the structure does not include any dative covalent bond. This is the answer from the mark scheme but I don't get how carbon will be gaining that electron when the negative sign is next to N. Also I searched this up but found that this ion involves a dative covalent bond.

Help?

Thanks
The "correct" structure does not differentiate between the electrons from the carbon, the nitrogen or the negative charge, after all they are all just electrons.

Three shared pairs and two lone pairs. The carbon has a formal charge of -1.

You can draw the structure with a dative bond, but you can also draw it without (as in the diagram).
3. (Original post by charco)
The "correct" structure does not differentiate between the electrons from the carbon, the nitrogen or the negative charge, after all they are all just electrons.

Three shared pairs and two lone pairs. The carbon has a formal charge of -1.

You can draw the structure with a dative bond, but you can also draw it without (as in the diagram).

So it is right that carbon is the atom receiving the electron? But why is the negative sign next to N, not C? I sometimes I see -CN. Thanks
4. (Original post by iqra2159)
???
5. (Original post by coconut64)
So it is right that carbon is the atom receiving the electron? But why is the negative sign next to N, not C? I sometimes I see -CN. Thanks
You usually write OH-, did you ask the question then, too?

Basically, you have carbon with its six e-, nitrogen with its seven and an extra electron.

Once they're all added together there is no way of knowing which electron started where, there just are sixteen in total. Who cares if you draw your triangle next to the C or N? The important thing is that there is a triple bond and two lone pair and an acknowledgement somewhere that an extra e- was required to make it happen, hence the CN- (or -CN).

Sometimes -OH is written for clarity.

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Updated: February 8, 2017
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