Using the molecular orbital energy ordering for second-row homonuclear diatomic molecules in whi

Using the molecular orbital energy ordering for second-row...

Key Concepts

MO Energy Diagrams

MO Energy Diagrams are graphical representations of the relative energy levels of molecular orbitals formed from atomic orbitals. These diagrams help visualize the order and occupancy of bonding, antibonding, sigma, and pi orbitals, and are crucial for predicting chemical bonding and reactivity as the total number of electrons in the system changes.

Magnetic Properties (Paramagnetism and Diamagnetism)

Magnetic properties in molecules are predicted by the presence of unpaired electrons in the molecular orbitals. A molecule with all electrons paired will be diamagnetic and weakly repelled by magnetic fields, while the presence of unpaired electrons leads to paramagnetism, causing the molecule to be attracted to magnetic fields. This concept is integral to understanding the electronic behavior of molecules and ions as described by their MO diagrams.

Bond Order Calculation

Bond order in molecular orbital theory is determined by subtracting the number of electrons in antibonding orbitals from the number in bonding orbitals, then dividing the result by two. This value indicates the strength and stability of the bond, with higher bond orders corresponding to stronger, more stable bonds. It is an important concept when comparing different molecules or ions with varying numbers of valence electrons.

Molecular Orbital Theory

Molecular Orbital Theory is a method for describing the electronic structure of molecules in which atomic orbitals combine to form delocalized molecular orbitals that extend over the entire molecule. This theory explains how electrons are distributed in bonding and antibonding orbitals and is essential for predicting properties such as bond order and magnetism in molecules.

Orbital Energy Ordering in Diatomic Molecules

In second-row homonuclear diatomic molecules, the specific ordering of the molecular orbitals—where the ? orbitals derived from 2p atomic orbitals lie at lower energy than the ? orbital from the same set—plays a critical role in determining the electronic structure. This ordering influences the filling of electrons in molecular orbitals and affects calculated bond orders and magnetic properties.

Transcript

00:01 Okay, in this problem, we're going to be talking about molecular orbital energy diagrams, as well as bond order and para versus diamagnetism.

00:10 So for this one, we're going to be basically looking at how many valence electrons anything could have, and figuring out the bond order and the magnetic properties of the resulting molecule.

00:22 So first, let's talk a little bit about bond order.

00:25 Bond order is just the strength, it's the measure of the strength of the bond.

00:30 And as long as it's not zero or negative, the bond will be stable.

00:34 And you can calculate it by the number of bonding or number of electrons in bonding orbitals minus the number of electrons in anti -bonding orbitals, and then divide that by two.

00:45 And then for para versus diamagnetism, a molecule is diamagnetic if all of its electrons are paired in orbitals.

00:53 And it's paramagnetic if it has some unpaired electrons.

00:57 And this is because the unpaired electrons fill up orbitals without an opposing spin.

01:03 And then once they get paired, it has another electron in there that's cancelling out its spin.

01:08 And so the unpaired spin is what helps it react to a magnetic field.

01:13 So let's start going down this list.

01:15 So if we have one valence electron, we're going to have, it's going to pop into this sigma 2s orbital.

01:25 And so we'll have one electron in a bonding orbital, nothing else.

01:29 So that's going to be one over two for the bonding order.

01:33 And it's going to be paramagnetic because this electron is unpaired.

01:37 From there, we're going to add another one for two valence electrons.

01:41 Here we have two electrons in a bonding orbital.

01:43 That's zero and then anti -bonding.

01:45 So we get two minus zero.

01:47 That's two divided by two is one.

01:50 So that's our bond order.

01:51 And it's diamagnetic now because they're both paired.

01:54 Up next, we put one in the anti -bonding orbital, and in this we're subtracting one from the total of the numerator of the bond order equation.

02:04 So we get 2 minus 1, which is 1, then divide that by 2.

02:07 We get 1 .0 .5, which is 1⁄2.

02:10 And this is paramagnetic because there's an unpaired electron in the anti -bonding orbital.

02:15 As we add one more, now our bond order is 0.

02:18 So this will actually be unstable because the bond order, there's the bond order is 0 or negative.

02:24 And this basically because the energy of putting electrons in the anti -bonding orbitals takes a lot of energy, and so it's more energy than is really helped or saved when you bond.

02:36 So this just won't happen.

02:38 But in theory, it would have a bond order of zero, and it would be diamagnetic because all the electrons are paired...

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