2. Purpose
• In the previous lesson we learned that the electrons are arranged in
sublevels within an atom. We can further separate electrons within a
sublevel into different orbitals. In this lesson, we will learn about orbitals
and how to assign electrons to them.
3. Orbital Definition
• An orbital is the region in space where you are most likely to find an
electron.
• Each orbital can hold up to two electrons
• Misconception Alert:
– An orbital is not an orbit. Electrons do not orbit a nucleus like planets
orbit the sun on a fixed path. Rather, an orbital simply defines the
space where you are most likely to find the electron.
4. Orbital Shapes
• Orbitals can take different shapes depending on the type of sublevel they
belong to.
• s-type orbital are spherical in shape:
• p-type orbital are considered dumbbell shaped:
• d-type orbitals can have one of the following shapes:
• f-type – do not worry about their shape
5. s-type sublevels have a single orbital
• Each s-sublevel can only hold two electrons. Since an orbital holds two
electrons, every s sublevel has only one orbital.
• Electrons in an s-sublevel occupy spherically shaped orbitals.
1s 2s 3s 4s
• Note: Notice that each p sublevel has similar orbitals, but as one gets higher
in energy level, the orbitals get larger.
6. p-type sublevels have 3 orbitals to hold the 6
electrons
• Each p-sublevel can only hold six electrons. Since an orbital holds two
electrons, every p sublevel has three orbitals.
• Electrons in a p-sublevel occupy dumbbell shaped orbitals.
• Note: Notice that each p sublevel has similar orbitals, but as one gets
higher in energy level, the orbitals get larger.
2p orbitals 3p orbitals
7. d-type sublevels have 5 orbitals to hold the 10
electrons
• Each d-sublevel can only hold ten electrons. Since an orbital holds two
electrons, every d sublevel has five orbitals.
• Electrons in a d-sublevel occupy orbitals with the following shapes:
– 4 of the 5 orbitals look like this:
– 1 of the 5 orbitals looks like this:
8. f-type sublevels have 7 orbitals to hold the 14
electrons
• We will not be concerned with the shapes of the f-type orbitals. Just know
that each f sublevel will have 7 orbitals.
9. We can now break our energy level diagram down
further by separating the orbitals within a sublevel
• To do this one simply breaks each p sublevel into 3 pieces, each d into 5,
and each f into 7 as shown on the energy diagram below.
Energy
1
2
3
4
1s
2s
2p
3s
3p
3d 4s
4p
4d
4f
10. To save space and put the sublevels in order, we
use boxes to designate orbitals
• Each box represent an orbital. The order of sublevels is the same that we
learned in our previous lesson.
• Note: The color was used so that it is clear which orbitals go with which
sublevel. Notice how each s has a single orbital, each p has three, and the
d has five.
1s 2s 2p 3s 3p 4s 3d 4p
11. Assigning electrons to orbitals is easy as long as
you follow these rules.
• When filling orbitals
– Make sure you know the electron configuration first: 1s2 2s2 …
– No more than two electrons can go in a box
– An arrow will represent the electron
– Electrons in the same box have opposite spins – this is shown with one
arrow up and one arrow down.
– Electrons stay unpaired within a sublevel if possible
– Unpaired electrons will have the same spin
12. Examples
• Show the orbital filling diagram of carbon.
– Electron configuration:
• 1s2 2s2 2p2
– Orbital filling diagram:
• Note: A few things to notice
– The electrons in 2p were kept separated. A third one would go in the
third box. The fourth will pair up with the first.
– The two unpaired electrons have arrows pointing the same way.
– Even though the third orbital in 2p does not have an electron, we still
show the box.
1s 2s 2p
13. Pause and Practice
• Write the complete orbital filling diagram for O.
• Write the orbital filling diagram for just the 3d electrons in Fe.
• Write the orbital filling diagram for just the 5p electrons in Br.
14. Pause and Practice Answers
• Write the complete orbital filling diagram for O.
• Write the orbital filling diagram for just the 3d electrons in Fe.
3d
• Write the orbital filling diagram for just the 5p electrons in Br.
5p
1s 2s 2p
