One bit of evidence that the quantum mechanical model is...

One bit of evidence that the quantum mechanical model is "correct" lies in the magnetic properties of matter. Atoms with unpaired electrons are attracted by magnetic fields and thus are said to exhibit paramagnetism. The degree to which this effect is observed is directly related to the number of unpaired electrons present in the atom. Consider the ground-state electron configurations for $\mathrm{Li}, \mathrm{N}, \mathrm{Ni}, \mathrm{Te}, \mathrm{Ba}$, and $\mathrm{Hg} .$ Which of these atoms would be expected to be paramagnetic, and how many unpaired electrons are present in each paramagnetic atom?

Key Concepts

Hund's Rule

Hund's Rule is a principle used in determining the electron configuration of atoms, stating that electrons will fill degenerate orbitals singly with parallel spins before pairing up. This rule is key to understanding how many unpaired electrons will be present in an atom, thereby influencing its magnetic properties.

Quantum Mechanical Model

The quantum mechanical model provides a detailed explanation of how electrons are distributed within atoms using probability clouds rather than fixed orbital paths. This model is foundational for understanding atomic behavior and chemical properties, as it explains the discrete energy levels and the allowed arrangements of electrons in atoms.

Electron Configuration

Electron configuration refers to the distribution of electrons among the various atomic orbitals. This arrangement is determined by energy levels and subshells, and it plays a critical role in predicting an element's chemical behavior, including its magnetic properties.

Unpaired Electrons

Unpaired electrons are electrons that occupy an orbital singly rather than in pairs. Their presence is crucial in determining the magnetic characteristics of an atom, because unpaired electrons create a net magnetic moment, which contributes to phenomena like paramagnetism.

Paramagnetism

Paramagnetism is a form of magnetism exhibited by atoms or molecules that have one or more unpaired electrons. These unpaired electrons interact with external magnetic fields, causing the material to be attracted to the magnetic field. The strength of this attraction is directly related to the number of unpaired electrons present.

Transcript

00:01 To determine if an atom is likely to exhibit paramagnetism or the property of having unpaired electrons, we look at the electron configuration.

00:10 Since these atoms are all in their ground state, we can look at just the valence electron configuration for each atom.

00:16 And remember, using the periodic table is a shortcut way to do this.

00:22 So, for example, for our first atom lithium, which is found right here, we know that its valence electron configuration is two, 2 s1 because remember that each column corresponds to a different configuration and this is the s block and so pretty quickly you can see that there's just one unpaired electron so lithium is in fact paramagnetic with one unpaired electron we can follow the same process for nitrogen nitrogen is found here so similarly it's a 2 s1 followed by p electrons or 2p3.

01:25 And so when we look at our valence electron configuration, the s and the p's, we see that while there are paired electrons in the s, there are three unpaired electrons in the p, making me think that nitrogen is also paramagnetic with three unpaired electrons.

01:59 Nickel, it's a little more complex with more electrons.

02:04 We have some d electrons, and we see that the valence electron configuration for nickel is 4s2, 3d8, and so the 2 s electrons are paired, and then we fill in the d's, spreading the electrons out first, and then pairing.

02:41 And so you can see that there are two unpaired electrons in nickel.

02:45 So nickel is also paramagnetic with two unpaired electrons...

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