Question

Hydrogen with 1s^2 would be similar to what other elements? Is this element paramagnetic?

Answer 1

Orbitals are mathematical functions. As such, addition and subtraction applies to them. Furthermore, only orbitals that have similar properties (symmetry) can be added or subtracted from each other. So in the case of a H2 molecule, each hydrogen atom has a 1s orbital with one electron in it. So let us call 1s1a and 1s1b. So can have then the addition:
1s1a + 1s1b = sigma (bonding orbital) and 1s1a - 1s1b = sigma* (antibonding orbital).

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sig*


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1sa 1sb


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sig


The two electrons want to be on the sigma orbital, which is the bonding orbital. Why? It is a molecular orbital that has lower energy than either of the two individual atomic orbitals and the sigma* antibonding orbital. We can deduce the bond order in H2 by 1/2(electrons sigma - electrons sigma*), for H2, is 1/2(2 - 0) = 1. The molecule H2^+ and H2^- does exist, it has H2^+ has a single electron in the sigma orbital so bond order is 1/2(1 - 0) = 1/2 and for H2^-, 1/2(2 - 1) = 1/2. Molecular orbital theory is very useful, since it allow us to predict properties of molecules. O2 is paramagnetic, (weakly magnetic), because it has two unpaired electrons in the pi* antibonding orbitals of O2. Pi and Pi* orbitals arise from the sideway overlap of p orbitals, in the case of O2, py and pz orbitals.