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Lewis Structure and Hybridization of HSCN (thiocyanic acid, hydrogen thiocyanide)

HSCN is the corresponding acid of SCN-, which is the thiocyanide ion. All four of these atoms are non-metals, the bonds between them will be covalent, and it will make a molecular compound.

Carbon brings four valence electrons with it, and so needs four more to complete its valence shell. Nitrogen brings five valence electrons, and so it needs three to completed its octet. Carbon and nitrogen share three electrons each (with each other) and a triple bond forms between them.

Meanwhile, carbon needs one more electron and sulfur can provide it. This also gives sulfur a seventh electron, and it gets its eighth from hydrogen.

HSCN has a single bond between H and S, a single bond between S and C, and a triple bond between C and N.

What is the hybridization of C in HSCN?

Carbon is triple-bonded to nitrogen; this requires two pi bonds and that means it requires two leftover p orbitals after hybridization; so the C is “sp” hybridized.

What is the hybridization of N in HSCN?

N is also triple bonded, so it is “sp” hybridized as well. The sigma bond (first bond between the two is sigma) and the lone pair are where the “hybridized sp orbitals” are used here.

What is the hybridization of S in HSCN?

The sulfur atom has NO double or triple bonds. It has two single bonds (both sigma) and two lone pairs. This means is does not need any leftover p orbitals (which would need to stay unhybridized) and so sulfur is “sp3” hybridized here.

What is the VSEPR shape of HSCN?

The carbon atom is only bonded to two other atoms and has no lone pairs; this gives it AX2 geometry, and so there is a linear arrangement around the carbon atom.

The sulfur, on the other hand, has two sigma bonds (single bonds on either side) AND two lone pairs. This gives it Ax2E2 geometry and so it is V-Shaped/Non-linear/Bent.

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Lewis Structure and Hybridization of HCN (hydrocyanic acid, hydrogen cyanide)

HCN has a hydrogen atom single-bonded to a carbon atom, and that carbon atom is triple-bonded to a nitrogen atom.

These are all non-metals, so the bonds are covalent and HCN is therefore a covalent (aka Molecular) structure.

Carbon brings four valence electrons with it; it needs four more to complete its valence shell. Hydrogen shares one electron with it, and nitrogen shares three. This completes carbon’s octet.

Carbon likewise shares one electron back with Hydrogen (this complete’s hydrogen’s outer shell of two electrons, aka Doublet) and carbon shares three electrons back with Nitrogen. This completes nitrogen’s octet.

You can watch this structure get drawn below, or you can scroll to the bottom of this page for a completed structure.

What is the hybridization of Carbon in HCN?

Carbon is triple-bonded to nitrogen, and so there are two pi bonds (Remember: The first bond between any two atoms is a sigma bond, and the second/third bonds are pi bonds). This means two p orbitals are required to be left over after hybridization.

2 pi bonds = 2 leftover p orbitals.

This means only ONE of carbon’s p orbitals is available to hybridize, and so the hybridization of C in HCN is “sp”.

What is the hybridization of N in HCN?

Nitrogen is triple-bonded to carbon, and so two pi bonds are required here as well. This means only one of nitrogen’s p orbitals is available to be hybridized, and so the hybridization of nitrogen in HCN is “sp”.

What is the molecular shape (VSEPR shape) of HCN?

Because the carbon is connected to two atoms, with no lone pairs on that central carbon, the geometry is AX2, which is “linear”. The bond angle is 180 degrees.

This image shows HCN with its constituent atoms, the sharing of electrons from one atom to another, and the final Lewis Structure showing a single bond to hydrogen and a triple bond to nitrogen.
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Lewis Structure of BCl3, Boron Trichloride (and Hybridization)

Boron Trichloride, BCl3, has three chlorine atoms surrounding a single boron atom.

This is because each chlorine brings seven valence electrons with it, and needs just one more electron to complete its octet.

Boron has three valence electrons to start with, but does not need a full eight electrons to be stable. It is a violation of the octet rule, but this is the way things are.

So, Boron shares ONE electron with each of three chlorine atoms, and each chlorine shares one electron with Boron:

The Lewis Structure of Boron Trichloride (BCl3) has three chlorine atoms surrounding a single boron atom.

This is a trigonal planar arrangement and implies that the boron must be sp2 hybridized. The extra unhybridized p orbital is empty, but its presence is what keeps the three sp2 orbitals separated by exactly 120 degrees.

I have a video where I draw this Lewis Structure, if you’re a visual learner:

Now, in reality, solid BCl3 is more complicated. The lone pairs on each chlorine atom are attracted to the wide-open slightly-positive charge on the Boron atom, and a Lewis Acid-Base reaction happens: That’s fancy chemistry talk for chlorine sharing its lone pair with boron.

This gives the boron atoms in solid BCl3 a tetrahedral geometry; since each of them actually connect with FOUR chlorines each. It makes the entire structure more like a lattice, rather than being individual molecules.