Difference Between Orbit And Orbitals

In chemistry, the terms orbit and orbital are frequently used, and this leads to confusion because we mistakenly think they both refer to the same thing. But hold on, do they similar to each other or do they differ in any way? 

In order to understand the behavior of atoms at the molecular level it is important to have the correct understanding of the terms orbit and orbitals. 
If we talk about an orbit, it is the circular or elliptical path followed by the electrons around the nucleus. These orbits have different energies and angular momentum. It plays a key role in writing the electronic configuration of atoms which affects many physical and chemical properties like shape, size, electronegativity, electron affinity, and chemical reactivity of an atom.

On the other hand, if we talk about Orbitals they are defined as the 3-Dimensional regions around the nucleus where. there is a high chance of finding an electron. These orbitals defined the shape, size, and orientation of the electron cloud and orbitals around the nucleus. These orbitals are characterized by a set of four quantum numbers defined in quantum chemistry. The overlapping of these orbitals with each other leads to the formation of various chemical bonds and help us in understanding various molecular orbital theory.

Thus, both orbit and orbital talk about the region and movement of electrons around the nucleus yet they have different terms and affect different properties. So let’s find out these terms in detail, their characteristics, and the differences between them in the article below.

What is Orbit?

Orbits are defined as the fixed path followed by the electron around the nucleus, in which electrons revolve around it. Like our earth and all other planets revolve around the sun. They have a fixed radius, and hence a fixed circumference. These are considered circular or elliptical.

• It is also known as the shell.
• It is represented as by n and depending on the value of n each orbit has its different nomenclature as follows:

          eg.   n= 1  K orbit 
                  n= 2  L orbit 
                  n= 3  M orbit 
                  n= 4  N orbit 

Characteristics of Orbits

1. Orbits are quantized means there are an infinite number of orbits around the nucleus but electrons are only present in that orbits in which their angular momentum is an integral multiple of h/2π.

• Formula : mvr = nh/2π  
• where,  n = no. of orbits
•  h = plank’s constant = 6.626*10-34 joule-seconds

 2. While revolving around the nucleus electrons neither lose nor gain energy therefore these orbitals are also called stationary orbits.

 3. Electrons can easily move from one orbit to another by absorbing or releasing energy equal to the energy difference b/w the two energy levels.

 4. The arrangement of electrons in orbits determines the chemical behavior and reactivity of the atom.

 5. The different numbers of electrons in orbits decide the position of the element in the periodic table.

History of Orbit:

•  In 1913, Neil Bohr first gave the concept of orbits in his atomic model called “Bohr’s Atomic Model“, which stated that “electrons are revolving around the nucleus in a circular path of constant radius called orbits“.

This atomic model follows classical mechanics and considers an electron a particle in nature. And only applies to single electron species like hydrogen or hydrogen-like atom.

• The required force for this motion is:

• Centripetal force = Electrostatic force of attraction between a nucleus (+ve) charge and an electron (-ve) charge.
  Formula = mv2/r = kZe2/r2

What is Orbital?

It is defined as the 3 Dimensional regions around the nucleus with a high chance of finding the electron. These are of different shapes, orientations, and electron densities around the nucleus. These orbitals are also called electron clouds or electron density around the nucleus.

For a given value of n orbit, there exist n² orbitals in it.
eg. n = 1 K shell, (1)2 = 1 orbital, 1s orbital only. 
     n = 2 L shell, (2)2 = 4 orbitals , 1 s and 3 p orbitals (2s, 2px,2py, and 2pz )
     n = 3 M shell, (3)2 = 9 orbitals, 1 s, 3 p, and 5 d orbitals (3s, 3px, 3py, 3pz, dxy,dyz, dzx, dx2-y2 and dz2

Shapes of different orbitals:

• S orbital: Spherical
• P orbital: Dumb-Bell in shape.
• D orbital: Double dumb-Bell in shape.
• F orbital: Complex in shape.

Characteristics of Orbitals

1. Orbitals are represented as a combination of alphabetical letters and numbers like 1s, 2p, 3d, 4f, etc.
2. Orbitals are obtained by solving the Schrodinger equation.
3.  It is determined by a mathematical function called the wave function, which helps find the probability of electrons around the nucleus.
4. Each orbital has a different shape, energy, and orientation except degenerate orbitals.
5. Each orbital accommodates a maximum of 2 electrons with opposite spins only.
6. The overlapping of different orbitals leads to the formation of different chemical bonds, which helps in determining the shapes and properties of the molecule.

History of Orbitals:

The whole concept of orbital was given by Heisenberg, Schrodinger, and Dirac in the late 1920s to explain the concept of quantum numbers and the structure of atoms.

• There are a total of 4 quantum numbers as follows:

1. Principle quantum number (n)
2. Azimuthal quantum number (l)
3. Magnetic quantum number (m)
4. Spin quantum number (s)

• This atomic model follows quantum mechanics and the electron is considered a wave by following two basic principles:

1.  De-Broglie Concept ( It considers the wave nature of the electron )
2.  Heisenberg Uncertainty principle (It believes in electron finding probability)

• There are different functions defined for the probability of finding the electron around the nucleus:

1. Radial Probability density ( ψ²(r) ) or ( R²(r) ): It gives the probability of finding electrons at a point and a distance “r” from the nucleus.
2. Radial Probability density function ( 4πr²ψ²(r) or ( 4πr²R²(r) ): It gives the probability of finding an electron in a spherical region or volume at a distance “r” from the nucleus.

Difference Between Orbit and Orbitals

S.No		Orbit	Orbitals
01.	Definition	It represents the fixed path followed by the electron around the nucleus.	It represents the region around the nucleus where there is a high chance of finding the electron.
02.	Examples	K, L, M, and L shells.	s, px, py, pz, and all d and f orbitals.
03.	Representation	It is represented by n.	It is represented by s,p,d, and f.
04.	No. of orbits and orbitals	If there are n number of orbits	for every n no. of orbit, there exist n2 orbitals
05.	Shape	It is either circular or elliptical in shape.	It is spherical, dumb-Bell, double dumb-Bell, and complex in shape.
06.	Dimension	It is 2 – Dimension in nature.	It is  3 – Dimension in nature.
07.	Maximum no. of electrons	The maximum no. of electrons in orbit is 2n2	The maximum no. of electrons in an orbital is 2, following Pauli’s Exclusion principle.
08.	The concept has been given by	Neil Bohr in 1913	Heisenberg, Schrodinger, and Dirac in 1927
09.	Heisenberg principle	Orbits do not follow this principle, as the position and momentum of an orbit can be easily determined simultaneously.	Orbitals follow this principle.
10.	Duality	The concept considers an electron as a particle.	The concept considers an electron as both a particle and a wave.

Conclusion

The concept of orbits was based on Classical mechanics and the old atomic model which believes that electrons revolve around the nucleus, which is not the real case. This was later improved by the Quantum mechanical model of the atom which believes that electrons have both particle and wave-like nature and we only find their probability around the nucleus by the probability distribution function.

Most of the concept was not explained by the existence of orbits only like the splitting of orbital in an electric and magnetic field called Stark and Zeeman effects, shapes of molecules, and chemical reactivity. Which was later explained by the concept of orbitals, and shows the real and more descriptive picture of electrons around the nucleus.

FAQs on Orbit and Orbitals

Q1. Why do different orbitals have different shapes?

Ans: It is because the shape of the orbital depends on the energy of the electron and it is determined by a mathematical function called the Schrodinger equation. 

Q2. How do electrons are filled in the orbitals?

Ans: Electrons are filled in the orbitals by following three rules: 

a) Aufbau rule or ( n+l ) rule: It states that the filling of electrons in orbital takes place in increasing order of their energies means lower energy orbital would fill first.

b) Pauli’s Exclusion Principle: It states that an orbital can accommodate a maximum of 2 electrons with opposite spins only.

c) Hund’s Rule of maximum multiplicity: It states that no pairing of electrons will occur until all the orbitals of a subshell are singly electron occupied and all the electrons have the same spin either all are clockwise or anticlockwise.

Q3. What is a node, and how can we determine them?

Ans: It is a region around the nucleus where the probability of finding an electron is zero. There are mainly two types of nodes possible around the nucleus:

a) Radial node, which lies on the radial part of the orbital.

b) Angular node, which lies on the angular part of the orbital.

Relationship between nodes: Total node = Radial node + Angular node

Formula: Total node = n-1

               Radial node = n-l-1

               Angular node = l (where n = principal quantum number and l = azimuthal quantum number)

Q4. Which quantum number represents orbital?

Ans: Magnetic quantum number ( m) represents the orbitals and different orientations of the electron’s cloud around the nucleus.in orbit

Q5. What are degenerate orbitals?

Ans: The orbitals having the same energy are called degenerate orbitals.

For Example: 3p and 4s have the same energy according to the Aufbau principle or (n+l) rule:

3p, n = 3 and l = 1 energy = (n+l), 3+1 = 4.

4s, n = 4 and l = 0 energy = (n+l), 4+0 = 4.