I'm drawing a Lewis structure for hydrogen cyanide using nitrogen with a valency of 3. Would I still need 2 dots after the N or would this represent nitrogen valency 5?
You need the two extra electrons for N at the end. Only the electrons involved BETWEEN the elements are bonding electrons; the others are used to fill orbtials but not for bonding purposes. Here is how you determine it.
H has 1 electron in the outer shell.
C Has 4 electrons in the outer shell.
N has 5 electrons in the outer shell.
10 electrons total. So ALL 10 electrons must be used. AND you try to place them such that two electrons are in the H sphere and 8 electrons for the other two elements.
H:C:::N:
The terminal (unpaired) electrons on N are used to make 8 electrons for N but those two are not involved in bonding. You see H has 1 bond, C has 4, and N has 3 (two dots, that is electrons) are equivalent to one (-) bond or 4 electrons are equivalent to a double (=) bond or 6 electrons are equivalent to a triple bond (but I can't draw a triple bond on the computer.
To draw the Lewis structure for hydrogen cyanide (HCN) using nitrogen with a valency of 3, you would follow these steps:
1. Count the total number of valence electrons in the molecule. In this case, hydrogen (H) has 1 valence electron, carbon (C) has 4 valence electrons, and nitrogen (N) has 5 valence electrons.
2. Add up the valence electrons: 1 (H) + 4 (C) + 5 (N) = 10 valence electrons.
3. Place the atoms in the correct order. In this case, it is H-C-N.
4. Start by placing the shared pairs of electrons (chemical bonds) between each atom. Hydrogen can only form 1 bond, so there will be a single bond between H and C. Carbon needs 4 electrons to complete its octet, so it will have a single bond with H and a triple bond with nitrogen.
5. Distribute the remaining electrons to fill the remaining valence electron slots. In this case, you have 4 electrons left after forming the bonds.
6. Place these remaining electrons on nitrogen until it satisfies its octet. In this case, place 2 dots (representing 2 electrons) next to N. The remaining 2 electrons will be placed on the carbon atom.
The Lewis structure for hydrogen cyanide using nitrogen with a valency of 3 would be:
H:C≡N:
Where the colon (:) represents the chemical bond between atoms, the triple bond (≡) represents the bonding between C and N, and the two dots (:) represent the unpaired electrons on nitrogen.