Lewis Structure of iron (III) oxide, Fe2O3, step-by-step

The Lewis Structure of iron (III) oxide, Fe2O3, consists of five ions: Two iron ions with a +3 charge each, and three oxygen ions with a -2 charge each.

Iron III oxide is an ionic compound, because it consists of a metal and non-metal. These types of atoms have a big enough electronegativity difference that electrons are *transferred* from one atom to another, rather than being shared.

To begin, we note that the iron atoms need a charge of +3 … this is evident in the chemical formula (Fe2O3), since the “3” on the O had to have been criss-crossed down from the iron. It is also obvious in the name: The Roman numeral (III) after iron indicates that its charge in this compound is +3.

So we draw two iron atoms with three valence electrons each.

Each oxygen atom brings 6 valence electrons (Oxygen is in Group 16 and is two electrons short of a full octet in its outer shell).

This image shows the transfer of electrons from Iron atoms to Oxygen Atoms, and the complete lewis structure of Iron (III) Oxide, Fe2O3.

One iron atom gives two electrons to an oxygen, but then still has one electron left. So it gives that electron to another oxygen, but that oxygen requires one more as well. So another iron atom must come into play; it gives one electron to complete the second oxygen’s octet and then gives away both of its leftover electron to a third oxygen.

This is an ionic compound, so there is no “hybridization of oxygen in Fe2O3” – it is instead a lattice of alternating positive and negative ions.

This structure likely reminds you of the lewis structure of Calcium Bromide (CaBr2), which was also ionic.


Lewis Structure of SCl2 and Hybridization of SCl2

The Lewis Structure of SCl2, sulfur dichloride, has a sulfur atom (which brings six valance electrons) bonded two chlorine atoms (which each bring seven valence electrons). By drawing the Lewis Structure accurately, we can determine the shape and hybridization of SCl2 as well.

Since chlorine needs to share just one extra electron to complete its octet, the sulfur is able to share each of its two unpaired electrons to form bonding pairs with chlorine.

Sulfur and Chlorine are both non-metals, which makes these bonds covalent. We can determine the type of covalent bond with a calculation of electronegativity difference: ΔEN = 3.16 – 2.58 = 0.58, which makes the bond polar covalent.

Substances with similar chemical formulas, such as CaBr2, are ionic and so their Lewis Structures are drawn very differently.

The lewis structure is shown here:

The Lewis Structure of SCl2, sulfur dichloride, has one sulfur single-bonded two each of two chlorine atoms.

The sulfur atom here has two bonding pairs (shown as horizontal lines) and two lone pairs (shown as two dots for each pair). None of these require pi-bonding (which is the method of formation for double and triple bonds). Thus, the hybridization of SCl2 is sp3.

In addition, because there are two bonding pairs and two lone pairs, we can say that the VSEPR notation is AX2E2 and the molecular shape is angular/bent. Indeed, the bond angle is significantly less than it would be in tetrahedral, since the lone pairs take up more space than bonding pairs. The bond angle in SCl2 is 103 degrees (Source).


Lewis Structure of Calcium Bromide (CaBr2) Step-by-Step

Calcium is a metal, in fact it is an alkaline earth metal in Group 2 of the periodic table. Bromine is a halogen in Group 17 and all of the halogens are non-metals.

When metals and non-metals react together, they form ionic compounds. This means that electrons are transferred from one atom to another, which creates positively-charged ions (cations) and negatively-charged ions (anions).

So how is calcium bromide (CaBr2) formed?

Since calcium has two valence electrons, and bromine has seven (which is one short of a full octet), ONE calcium atom will give away ONE electron to each of two bromine atoms. I use single-headed arrows to show that here:

This leaves you with a calcium atom that has lost two electrons and therefore has a +2 charge. I know it’s weird that losing something causes it to become plus-charged, but electrons are negative so it’s like you’re subtracting negatives.

The bromine atoms on the other hand gained one electron each, and therefore they now each have a -1 charge.

These charged particles are shown with their new numbers of valence electrons (zero for calcium, eight for each bromine) and are put in square brackets with the charge written in the top right corner:

Some teachers will allow you to show the two bromine ions this way:

But confirm that with your teacher first.

Want to watch me explain it instead? Here you go:


Lewis Structure of PCl3 and Hybridization of PCl3

PCl3 is a covalently-bonded molecule which is officially named phosphorus trichloride. It has three chlorine atoms around a single phosphorus atom, and that phosphorus also has a lone pair of electron which complete its octet.

Its lewis structure is shown below:

The phosphorus atom in the centre needs three single bonds and needs room for one lone pair of electrons. None of these require pi-bonding, which would result in needing unhybridized 3p orbitals.

Thus, the 3s orbital and all three 3p orbitals hybridize together to form four degenerate sp3-hybridized orbitals. “Degenerate” means they are all the same energy as each other. They are higher in energy than the 3s but lower in energy than the three 3p orbitals that were ‘used’ to make them.

sp3 hybridization usually leads to a tetrahedral shape, and if you are asked for Electron Pair Geometry, your teacher wants to hear tetrahedral. But because one of those four hybridized orbitals is a lone pair, there isn’t really anything there – just space where the electron ‘probably’ is.

The molecular geometry of PCl3 is trigonal pyramidal and its VSEPR notation is AX3E. The “A” represents the central atom (the phosphorus), each X represents a chlorine atom, and the E represents the lone pair.

You can watch me draw the Lewis Dot Diagram for PCl3 here:

Previously on this blog, I showcased why CH3F is tetrahedral and has AX4 VSEPR notation.


CH3F Lewis Structure and CH3F Hybridization

The answer your teacher wants to hear is that CH3F hybridization is sp3. CH3F (also known as methyl fluoride or fluoromethane) has a tetrahedral centre and bond angles of 109.5 degrees. The VSEPR notation for a molecule like this is AX4 or AX4E0. You might be more familiar with similarly-shaped molecules like methane and dichloromethane.

The carbon has sp3 hybridization, and the fluorine is sp3 hybridized as well. Hydrogen atoms do not hybridize, so that does not apply here.

The Lewis Structure is shown here. It has three hydrogen atoms single-bonded to carbon, and one fluorine atom single-bonded to the same carbon atom.


and you can watch it get drawn here, which emphasizes the tetrahederal shape and CH3F hybridization: