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Difference Between Shell and Orbit

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Last updated date: 19th Feb 2024
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What is Shell and Orbit: Introduction

Atoms are the fundamental units of matter, and for a long time, scientists believed that they were indivisible. However, further exploration of subatomic particles revealed that atoms can indeed be divided into smaller components. These subatomic particles include electrons, protons, and neutrons, with protons and neutrons forming the nucleus at the center of an atom.


Electrons, on the other hand, orbit around the nucleus in specific pathways. Although the exact position of an electron cannot be determined precisely, it follows probable paths known as shells, subshells, and orbitals. Shells and subshells consist of electrons with the same principal quantum number and angular momentum quantum number, respectively. In contrast, orbitals contain electrons with different spins but at the same energy level. This distinction is the primary difference between shells, subshells, and orbitals.

Shell in Atomic Structure:

Shell: The electrons around an atom's nucleus follow a pathway known as a shell, which is also referred to as an energy level. These shells are arranged according to the energy of the electrons they contain, with the lowest energy shell being closest to the nucleus. The subsequent energy level is located beyond the previous shell. To identify these shells, they are designated with letters such as K, L, M, N, and so on. The shell with the lowest energy level is called the K shell. However, scientists have assigned names to these shells using quantum numbers.


Quantum Number:

Each shell has its own specific quantum number, known as the principal quantum number. Consequently, the shell with the lowest energy level is designated as n=1. It's important to note that not all shells have the same capacity for electrons. The lowest energy level can accommodate a maximum of 2 electrons, while the next energy level can hold up to 8 electrons. As a result, the maximum number of electrons any shell can hold is 32, and no shell can exceed this limit. Higher shells have a greater electron capacity compared to lower shells. The existence of these shells indicates that the energy of an atom is quantized, meaning there are distinct energy values for electrons moving around the nucleus. Electrons within these shells can transition from one shell to another by either absorbing or releasing energy. However, for such a transition to occur, the amount of energy absorbed or released must match the energy difference between the two shells. If the energy difference is not equal, the transition will not take place.


Orbit of an Atom:

Orbit: An orbit refers to the specific path or region followed by an electron around the nucleus of an atom. In simpler terms, an orbital provides a precise description of how an electron moves. A subshell, on the other hand, consists of multiple orbitals. The number of orbitals present in a subshell varies depending on the specific subshell. Therefore, the quantity of orbitals within a subshell is a distinct characteristic of that subshell. However, it's important to note that each orbital can accommodate a maximum of two electrons. These electrons occupy the same energy level but possess different spins, always being paired with opposite spins. According to the Hund's Rule, when filling electrons into the orbitals, each orbital within a subshell is singly occupied before any of them become doubly occupied.


Let's explore the concepts of shell and orbit through real-life examples.


Example 1: Atomic Structure 

Consider the element carbon (C). The carbon atom has a nucleus consisting of protons and neutrons, and electrons occupy different energy levels or shells around the nucleus. The first shell (n = 1) can hold a maximum of 2 electrons, while the second shell (n = 2) can hold up to 8 electrons. In the case of carbon, the first shell contains 2 electrons, and the second shell contains 4 electrons, for a total of 6 electrons.

 

Example 2: Celestial Bodies 

Let's consider the Earth's orbit around the Sun. The Earth follows an elliptical orbit around the Sun, with the Sun located at one of the foci of the ellipse. This orbit is governed by the gravitational force between the Sun and the Earth. The Earth's orbital path determines its position relative to the Sun, affecting the seasons, climate, and other astronomical phenomena.


These real-life examples highlight the practical applications of shells and orbits in atomic structure and celestial dynamics. Shells help determine the electron configuration and chemical properties of atoms, while orbits describe the motion and positional relationships of celestial bodies.


Difference Between Shell and Orbit

Sr. No. 

Category

Shell

Orbit

1

Definition

Specific energy level or electron cloud surrounding the atomic nucleus.

The most probable region where an electron can be found within a shell. 

2

Representation

Shells are represented by principal quantum numbers (n).

Orbitals are represented by a combination of principal quantum numbers (n), azimuthal quantum numbers (l), magnetic quantum numbers (m), and spin quantum numbers (s).

3

Energy Levels

Each shell has a different energy level, with the innermost shell having the lowest energy and the outermost shell having the highest energy.

The energy of orbitals within a shell is the same.

4

Maximum Electron Capacity

Each shell can hold a maximum number of electrons based on the formula $2n^2$, where n is the principal quantum number.

Each orbital can hold a maximum of two electrons with opposite spins. 

5

Arrangement

Shells are arranged in ascending order of energy levels, with electrons filling lower energy shells before occupying higher energy shells.

Orbitals are arranged within a shell based on their energy and are filled according to the Aufbau principle, Hund's rule, and the Pauli exclusion principle. 

6

Spatial Distribution

Shells are represented as concentric spherical regions surrounding the nucleus.

Orbitals have different shapes (spherical, dumbbell, etc.) and orientations (x, y, z axes) within a shell.

7

Relationship

Shells contain one or more orbitals.

Orbitals are subsets of shells, with different orbitals within a shell corresponding to different energy states of the electron.

Summary

In atomic structure, shells and orbitals play crucial roles in understanding the distribution and behavior of electrons within an atom. Shells represent energy levels or electron clouds surrounding the atomic nucleus, while orbitals describe the most probable regions where electrons can be found within a given shell. Shells are characterized by principal quantum numbers, and each shell can hold a specific number of electrons. Orbitals, on the other hand, describe the pathways or regions where electrons move. The arrangement of electrons in shells and orbitals determines the chemical properties and reactivity of atoms. Together, shells and orbitals provide a framework for explaining the atomic structure and electron configuration.

FAQs on Difference Between Shell and Orbit

1. What is the relationship between shells and orbitals in an atom?

Shells and orbitals are related concepts in atomic structure. Shells represent specific energy levels or electron clouds surrounding the atomic nucleus, while orbitals describe the most likely paths or regions where electrons can be found within a given shell. Each shell consists of one or more orbitals, and each orbital can hold a maximum of two electrons. The number and arrangement of orbitals within a shell depend on the principal quantum number (n) associated with that shell.

2. How do electrons occupy shells and orbitals?

Electrons occupy shells and orbitals based on the principle of Aufbau, Hund's rule, and the Pauli exclusion principle. According to the Aufbau principle, electrons fill the lowest energy level (shell) first before moving to higher energy levels. Within a shell, electrons occupies different orbitals one by one, following Hund's rule, which states that electrons prefer to occupy separate orbitals with the same energy level before pairing up. The Pauli exclusion principle states that each electron in an orbital must have opposite spins.

2. Can an electron jump between different shells or orbitals?

Electrons can jump between different energy levels (shells) by either gaining or losing energy. This phenomenon is observed in processes such as the absorption or emission of energy in the form of photons. However, during normal atomic behavior, electrons tend to occupy the lowest available energy level (shell) before moving to higher levels. Within a shell, electrons can move between different orbitals with the same energy. These transitions between orbitals or shells are governed by the energy changes within the atom.