What is the Order of Energy of Orbitals (s, p, d, f)?
Energy of Orbitals is essential in chemistry and helps students understand various practical and theoretical applications related to atomic structure, periodic trends, and chemical bonding. Mastering this concept helps you predict how elements react and form compounds—a core part of exams and tests.
What is Energy of Orbitals in Chemistry?
The energy of orbitals refers to the amount of energy possessed by an electron occupying a specific atomic orbital (like 1s, 2s, 2p, etc.) in an atom. In simple words, it’s how ‘tightly’ or ‘loosely’ an electron is held by the nucleus depending on its position (shell and subshell). This concept appears in chapters related to atomic structure, electronic configuration, and chemical periodicity, making it a foundational part of your chemistry syllabus.
Molecular Formula and Composition
The concept of energy of orbitals does not have a single molecular formula since it applies to electrons in atoms of all elements. Instead, the energy depends on the quantum numbers ‘n’ (principal) and ‘l’ (azimuthal), which together define each orbital, such as 1s (n=1, l=0), 2p (n=2, l=1), 3d (n=3, l=2) and so on.
Preparation and Synthesis Methods
You don’t "prepare" an energy of orbital in the lab, but you can calculate orbital energies theoretically or observe them in atomic spectra experiments. These calculations start from the Bohr model for the hydrogen atom, then use quantum mechanics for multi-electron atoms. The famous (n + l) rule or Aufbau principle helps you determine the order in which orbitals are filled in an atom.
Physical Properties of Energy of Orbitals
Energy of orbitals is a theoretical property, not a physical one like boiling point or density. However, each orbital has a distinct energy level. In hydrogen, all subshells of a given n have identical energy, but in other atoms, s, p, d, and f orbitals within the same shell have slightly different energies due to electron-electron repulsion and shielding effects.
Chemical Properties and Reactions
The way electrons occupy these orbitals directly affects an atom’s chemical reactivity, the kinds of bonds it can form, and the colors or magnetic properties of compounds. For example, transition metals exhibit colorful compounds due to d-orbital energies. The pattern of orbital energies is crucial for understanding transition elements and their multiple oxidation states.
Frequent Related Errors
- Confusing orbital energy order (especially 4s vs 3d) when writing electronic configurations.
- Assuming all orbitals of the same shell are degenerate (same energy) in multi-electron atoms.
- Forgetting to use the (n + l) rule for multi-electron atoms.
- Not recognizing that hydrogen’s orbital energy sequence differs from all other elements.
Uses of Energy of Orbitals in Real Life
Understanding energy of orbitals is crucial in explaining the chemical properties of all elements, the arrangement of the periodic table, why metals conduct electricity, and how chemical bonds form in everything from medicines to plastics. It’s also the basis for technologies such as spectroscopy, chemical analysis, and even quantum computers!
Relation with Other Chemistry Concepts
Energy of orbitals is closely related to the concepts of quantum numbers and electron configuration. It ties directly into periodic trends, such as atomic size and ionization enthalpy, and helps explain the concept of degenerate orbitals and the order in which electrons fill subshells (Aufbau principle).
Step-by-Step Reaction Example
- Calculate the energy of an electron in the second shell (n=2) of a hydrogen atom.
1. Use the formula: En = -13.6 eV / n²
2. Substitute n = 2: En = -13.6 / (2)² = -13.6 / 4 = -3.4 eV
3. Final Answer: The energy of the 2nd shell in hydrogen = -3.4 eV - Determine which has lower energy: 4s or 3d orbital.
1. Find n+l for each orbital:
– 4s: n=4, l=0 → n+l=4
– 3d: n=3, l=2 → n+l=5
2. The orbital with lower (n+l) fills first: 4s fills before 3d, so 4s has lower energy.
Lab or Experimental Tips
Remember the energy order of orbitals with the diagonal or Aufbau diagram. In Vedantu live classes, educators use rhymes or arrows to help students quickly recall tricky sequences like 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p. Using colored charts and drawing arrows is a powerful memory aid for atomic structure topics!
Try This Yourself
- Write the Aufbau sequence up to 4p.
- Calculate the energy (in eV) of an electron in the third shell (n=3) for hydrogen.
- Explain why 2p and 2s orbitals have the same energy in hydrogen.
- Give two uses of orbital energy concepts in real life.
Final Wrap-Up
We explored the energy of orbitals—from its definition and order to its role in electronic configurations and periodic trends. Knowing orbital energies helps you solve many chemistry puzzles and ace exams, plus makes science in daily life more understandable! Find more easy explanations and tips on Vedantu to make chemistry your strength.
FAQs on Energy of Orbitals Explained: Order, Formula, and Sequence
1. What is the energy of orbitals in Chemistry?
The energy of orbitals refers to the amount of energy associated with an electron occupying a specific atomic orbital. It determines the electron’s stability and its position relative to the nucleus. Lower energy orbitals (like 1s) are closer to the nucleus and filled first, while higher energy orbitals (like 3d or 4f) are filled later as per the Aufbau principle.
2. How do you calculate the energy of an orbital?
For hydrogen-like atoms:
Energy (En) = –13.6 eV/n²
where n is the principal quantum number.
For multi-electron atoms:
- The (n+l) rule is used to estimate relative orbital energy.
- More electron shielding and subshell interactions occur.
Use quantum numbers and the atom’s structure to determine energy order.
3. What is the order of energy of s, p, d, f orbitals?
The general energy order of orbitals according to the (n+l) rule is:
1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s.
This sequence helps predict electron configuration in atoms.
4. What is the meaning of 1s, 2s, 2p, 3s, 3p in orbitals?
1s, 2s, 2p, 3s, 3p are names for atomic orbitals:
- The first number (n) shows the principal quantum number (energy level).
- The letter (s, p, d, f) represents the orbital type/subshell.
For example, 2p means principal quantum number 2, p-orbital subshell.
5. Are all orbitals in the same subshell degenerate?
Yes, all orbitals within the same subshell (like three 2p orbitals or five 3d orbitals) are called degenerate because they have equal energy in the absence of external fields or electron-electron interactions. Degeneracy is removed if outside forces or interactions are present.
6. Which orbital has highest energy in the periodic table?
Higher energy orbitals are filled last in the periodic table. For known elements, orbitals with the highest principal quantum number (such as 7p, 6d or 5f) have the highest energy and are populated in very heavy elements at the bottom of the periodic table.
7. Why does the energy order of orbitals differ between hydrogen and multi-electron atoms?
In hydrogen atoms, all orbitals with the same principal quantum number (n) have equal energy due to only one electron. In multi-electron atoms, electron-electron repulsion and shielding cause orbitals with different l values to differ in energy, so (n+l) rule applies, changing the energy order.
8. How does electron shielding affect orbital energy order?
Electron shielding occurs when inner electrons block outer electrons from the nucleus, reducing nuclear attraction. This causes s orbitals (more penetrating) to become lower in energy compared to p, d, or f orbitals in the same shell, changing the energy sequence, especially in multi-electron atoms.
9. What quantum numbers determine orbital energy?
Principal quantum number (n) and azimuthal quantum number (l) together decide the energy of an orbital, especially in multi-electron atoms.
- Lower (n+l) means lower energy.
- If (n+l) is the same, the lower n has lower energy.
10. Can two orbitals from different shells ever be degenerate?
In a hydrogen atom, orbitals from different subshells but the same n value (such as 2s and 2p) are degenerate. In multi-electron atoms, due to electron-electron repulsion and shielding, this degeneracy is removed, so orbitals from different shells are not degenerate.
11. Why does the 4s orbital fill before 3d?
The 4s orbital fills before 3d because its (n+l) value is lower (4s: n=4,l=0=4; 3d: n=3,l=2=5), and when (n+l) is the same, the orbital with lower n energy fills first. Thus, 4s is filled prior to 3d in most elements.
12. How do transition metals break standard energy order?
Transition metals sometimes break the standard orbital energy order due to small energy differences between 4s and 3d orbitals. After initial filling, electrons may occupy 3d before 4s during ionization or abnormal electron configurations, causing exceptions in electron arrangement.
