Atomic Orbitals Energies And Shapes
Learn and apply Atomic Orbitals Energies And Shapes in the published Chemistry course sequence.
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The core idea
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H1 Atomic Orbitals: Orientation
Orbital questions test three different ideas together: capacity, relative energy and shape. Keep these separate before combining them.
Definitions (Must Know)
- An orbital is a region of space around the nucleus with a high probability of finding an electron.
- An s subshell contains one orbital; a p subshell contains three orbitals of equal energy.
Detailed Explanations
The 1s, 2s and 3s orbitals are all spherical, with increasing size and energy as principal quantum number rises. The 2p and 3p subshells each contain three orbitals oriented along different axes. Shape does not mean an electron follows a fixed path.
The three p orbitals within one subshell are degenerate: they have equal energy but different spatial orientations.
An orbital drawing is a probability boundary, not the path followed by an electron.
Worked Examples
Modelled example 1
Core orbital capacity
Problem
How many orbitals and electrons can a 3p subshell contain?
Study the worked solution
State the orbital count
Method
Recall that every p subshell contains three orbitals.Reason
The p orbitals are three different spatial orientations of the same subshell.Working
Orbitals in 3p = 3.Calculate the electron capacity
Method
Allow two electrons in each orbital.Reason
Two is the maximum occupancy of any one orbital.Working
Maximum electrons = 3 × 2 = 6.
Guided practice 2
Compare 2s and 2p
Problem
State the number, relative energy and maximum electron capacity of the orbitals in 2p compared with 2s.
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Hints
Hint 1: compare orbital counts
Hint 2: compare within one shell
View solution step by step
Describe 2s
Method
State its orbital count, shape and capacity.Reason
An s subshell contains one spherical orbital holding at most two electrons.Working
2s: one spherical orbital, maximum two electrons.Describe 2p
Method
State its orbital count and total capacity.Reason
A p subshell contains three equal-energy orbitals, each holding at most two electrons.Working
2p: three p orbitals, maximum six electrons.Compare their energies
Method
Place 2s below 2p.Reason
Within the same principal shell, an s subshell is lower in energy than p.Working
E(2s) < E(2p).
Common misconception 3
Separate Orientation from Energy
Learner claim
A learner says, “The three 2p orbitals point in different directions, so they must have three different energies.” Identify the error and correct the statement.
Judge the energies
View solution step by step
Name the shared property
Method
State that all three orbitals belong to the same 2p subshell.Reason
Orbitals within that subshell are degenerate.Working
E(2pₓ) = E(2p_y) = E(2p_z).Retain the real difference
Method
State that their spatial orientations differ.Reason
Orientation distinguishes the three mutually perpendicular p orbitals without changing their energy.Working
Equal energy; different directions in space.
Examiner practice 4
Compare 3s and 3p Orbitals
Problem
Compare the 3s and 3p subshells in terms of orbital shape, number of orbitals, maximum electron capacity and relative energy. [6 marks]
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View solution step by step
Describe 3s
2 marksMethod
State its shape, count and capacity.Reason
An s subshell contains one spherical orbital.Working
3s: spherical; one orbital; maximum two electrons.Describe 3p
3 marksMethod
State its shapes, count and capacity.Reason
A p subshell contains three mutually perpendicular dumbbell-shaped orbitals.Working
3p: three dumbbell orbitals; maximum six electrons.Compare energy
1 markMethod
Place 3s below 3p.Reason
Within the same shell, s is lower in energy than p.Working
E(3s) < E(3p).
Self-mark with the mark scheme
Compare your response with each mark point. Select a point only when your response contains that evidence.
Credit the s description, three distinct p properties and relative-energy comparison.
Challenge 5
Transfer s/p Rules to the Fourth Shell
Problem
Without drawing them, compare the 4s and 4p subshells by number of orbitals, total electron capacity and relative energy within the n = 4 shell.
Try this before viewing the solution
Hints
Hint 1: ignore the changed shell number
Hint 2: apply the same-shell energy rule
View solution step by step
Apply the s rule
Method
Assign one orbital and two-electron capacity to 4s.Reason
Every s subshell has one orbital.Working
4s: one orbital, maximum two electrons.Apply the p rule
Method
Assign three orbitals and six-electron capacity to 4p.Reason
Every p subshell has three orbitals.Working
4p: three orbitals, maximum six electrons.Compare energy
Method
Place 4s below 4p within the same shell.Reason
The reviewed same-shell ordering is s below p.Working
E(4s) < E(4p).
Mind Stretchers
Attempt each transfer task before opening the hint.
Mind stretcher 1: Interpreting unfamiliar orbital dataExtension
A spectrum suggests three states of equal energy above one lower state in the same shell. Identify the subshells and justify your answer.
Show Hint
Connect the number of orbitals to s and p subshell capacities.
Show Answer
The single lower state is the s orbital. The three equal-energy states are the three p orbitals. Within one shell, the s subshell is lower in energy than p.
Mind stretcher 2: Correcting a modelExtension
A student draws an electron circling around the edge of a dumbbell-shaped p orbital. Explain two defects in the model.
Show Hint
Separate probability from trajectory, then check the complete p subshell.
Show Answer
The boundary represents a region of high probability, not a fixed path. A p subshell also contains three mutually perpendicular p orbitals, not one orbiting track.