How is it that so many planes are able to fly without running into each other?
The flight path of a commercial airliner is carefully regulated by the Federal Aviation Administration. Each airplane must maintain a distance of five miles from another plane flying at the same altitude and 2,000 feet above and below another aircraft (1,000 feet if the altitude is less than 29,000 feet). So, each aircraft only has certain positions it is allowed to maintain while it flies. As we explore quantum mechanics, we see that electrons have similar restrictions on their locations.
Orbitals
We can apply our knowledge of quantum numbers to describe the arrangement of electrons for a given atom. We do this with something called electron configurations. They are effectively a map of the electrons for a given atom. We look at the four quantum numbers for a given electron and then assign that electron to a specific orbital.
s Orbitals
For any value of \begin{align*}n\end{align*}, a value of \begin{align*}l=0\end{align*} places that electron in an s orbital. This orbital is spherical in shape:
p Orbitals
From Table below we see that we can have three possible orbitals when \begin{align*}l=1\end{align*}. These are designated as p orbitals and have dumbbell shapes. Each of the p orbitals has a different orientation in three-dimensional space.
d Orbitals
When \begin{align*}l=2\end{align*}, \begin{align*}m_l\end{align*} values can be -2, -1, 0, +1, +2 for a total of five d orbitals. Note that all five of the orbitals have specific three-dimensional orientations.
f Orbitals
The most complex set of orbitals are the f orbitals. When \begin{align*}l=3\end{align*}, \begin{align*}m_l\end{align*} values can be -3, -2, -1, 0, +1, +2, +3 for a total of seven different orbital shapes. Again, note the specific orientations of the different f orbitals.
Principal Quantum Number \begin{align*}(n)\end{align*} | Allowable Sublevels | Number of Orbitals per Sublevel | Number of Orbitals per Principal Energy Level | Number of Electrons per Sublevel | Number of Electrons per Principal Energy Level |
1 | s | 1 | 1 | 2 | 2 |
2 |
s p |
1 3 |
4 |
2 6 |
8 |
3 |
s p d |
1 3 5 |
9 |
2 6 10 |
18 |
4 |
s p d f |
1 3 5 7 |
16 |
2 6 10 14 |
32 |
Summary
- There are four different classes of electron orbitals.
- These orbitals are determined by the value of angular momentum quantum number \begin{align*}l\end{align*}.
Review
- What is an electron configuration?
- How many electrons are in the \begin{align*}n=1\end{align*} orbital?
- What is the total number of electrons in a p orbital?
- How many electrons does it take to completely fill a d orbital?