# What is quantum chemistry?

What is quantum chemistry?

Quantum chemistry is the branch of theoretical chemistry that applies quantum mechanics to study the behavior and properties of sub-particles of an atom, especially the electron.

## What is an orbital?

An orbital is a region where there is a high probability of finding an electron.

There are basic principles that determine the orbital and orbital configuration.

### Aufbau’s Principle

Aufbau’s principle states that in the building up of an atom, electrons will occupy orbitals of lower energy levels before occupying orbitals of higher energy levels.

### Aufbau’s principle focuses on the energy levels of orbitals.

It is important to note that filing up electrons in orbitals, you need to understand that electrons must not exceed the capacity of the orbital they occupy.

### Hund’s rule of maximum multiplicity

Hund’s rule of maximum multiplicity states that pairing will not start in degenerate orbitals until all the electrons have been singly occupied.

### But what are degenerate orbitals?

Degenerate orbitals are orbitals of the same energy levels or same energies.

It is important to mention that the s sub level has only one orbital, p sub level has three orbitals, d sub level has five orbitals while the d orbital has seven orbitals.

P sub-level has three orbitals.

d sub-level has five orbitals

F sub level has 7 orbitals.

Although, these are commonly called d orbitals, f orbitals, etc.

A single orbital has a maximum of two electrons, so in an s sublevel, we have two electrons, in a p sublevel we have six electrons, in a d sub level we have ten electrons while in an f sub-level we have fourteen electrons.

### Pauli’s exclusion principle

Pauli’s exclusion principle states that no two electrons in an orbital will have a set of values for all the four quantum numbers.

Paul’s exclusion principle focuses on quantum numbers.

## What is quantum number in chemistry?

Quantum numbers are the set of numbers applied in describing the position and energy of an electron in an atom.

So a quantum number is a number that occurs in the theoretical expression for the value of some quantized property of a subatomic particle, atom, or molecule and can only have certain integral or half-integral values.

### What is quantum and its types?

Quantum numbers are the set of numbers used to describe the position and energy of an electron in an atom. There are four types of quantum numbers:

### What is quantum chemistry used for?

Quantum chemistry help in predicting the chemical and physical properties of molecules and atoms.

The application of quantum chemistry which is useful on sciences and Engineering is very important to us. The challenge is in the computational and theoretical calculations of large numbers.

### What is the meaning of quantum mechanics in chemistry?

The four quantum numbers and examples

There are typically four quantum numbers namely Principal, azimuthal, Magnetic and electron spin quantum numbers.

The quantum numbers represent various things and give us a lot of information about an electron.

## Four quantum numbers in chemistry

I’ll talk about the four quantum numbers and their significance.

The four quantum numbers are designated by different letters.

The four quantum numbers are as follows;

**a. Principal quantum number, denoted by n.**

**b. Orbital angular momentum quantum number (or azimuthal quantum number), denoted by l.**

**C. Magnetic quantum number, denoted by ml.**

**d. The electron spin quantum number, denoted by s.**

### Explanation of quantum numbers and significance

## Principal quantum number (n)

The Principal quantum numbers are denoted by the symbol ‘n’

The principal quantum number represents the number of electron shells or energy levels.

Please you need to understand that there is a difference between the shell(orbit) and the orbital.

The orbit or shell is simply the distance between the nucleus and the electrons.

The orbital is a region where there is a high probability of finding an electron.

So it implies that a larger principal quantum number implies a greater distance between the electron and the nucleus and consequently a larger atomic size.

### Can the principal quantum number be zero?

Actually, the quantum number (n) cannot be zero. The quantum numbers used in describing electrons are always integers

In conclusion, the principal quantum number represents shells.

Please remember that the principal quantum number denotes the energies of the electron shells.

The sequence is thus tabulated

K < L < M < N < O…..

1 < 2 < 3 < 4 < 5…

## Azimuthal quantum number

The Azimuthal quantum number is otherwise called the orbital angular quantum number denotes or represents the shape of an orbital.

The nodes in an orbital help in determining the shape of the orbital.

**How many nodes are in each orbital?**

In an orbital, there are two nodes at the end of each orbital. The number of nodes is usually one less than the principal quantum number.

**How many nodes are there in 3s,3p, and 3d orbital?**

There are specific radial nodes in each orbital.

There are 2, 1, and 0 nodes in 3s,3p, and 3d orbitals respectively.

### How many nodes are there in 4s and 3p orbital?

4s orbital has 3 radial nodes plus 0 angular nodes, and 3p orbital has 2 nodes.

How do you determine the azimuthal quantum number of an element?

The Azimuthal quantum number is determined by l =n-1

For example;

For the first shell, K, n=1

Then l= l-1

So, 1-1=0

For the second shell, L, n=2

Then l=2-1=1

So, -1,0,+1

For the third shell, M, n=3

Then l= 3-1=2

So,-2,-1,0,+1,+2

## Magnetic quantum number(m)

The Magnetic quantum number simply defines the orientation in space of a given orbital of a particular energy level (principal quantum number) and shape ( azimuthal quantum number).

The term ‘magnetic’ is used because the quantum number was discovered in the presence of a magnetic field.

What is the formula for finding a magnetic quantum numbers?

The formula of the magnetic quantum number is (2l + 1).

The magnetic quantum number formula is used in predicting the orientation of the orbital.

For example, if n = 3 and l = 2 in an atom, the possible values of the magnetic quantum number are -2, -1, 0, +1, and +2.

The total sum number of orbitals in a given subshell is a function of the ‘l’ value of that orbital.

How are magnetic numbers assigned?

## Spin Quantum Number

The spin quantum number represents the direction of the spin of the electrons.

This could be either in the direction of clockwise or anti-clockwise and has the symbol s.

The spin quantum number has two possible values: s= +1/2 for spin up and s = -1/2 for spin down.

## Summary and significance of the quantum numbers

magnetic field.

Quantum numbers | Symbol | Possible values | Significance |

Principal quantum number | n | 1,2,3,4……. Using K, L, M, N…. | Energy levels or shells |

Azimuthal quantum number | l | 0,1,2,3……. Using n-1 | Shape of orbital |

Magnetic quantum number | m | -l…-3,-2-1.0.+1,+2,+3 | Orientation in space |

Spin quantum number | s | +1/2 .-1/2 | Direction |

## Is quantum an electronic configuration in chemistry?

There are several quantum number problems that we will look at to help us understand the quantum cjemistry.,

Some examples of elements and their configuration

Sodium Na = 1s^{2} 2s^{2} 2p^{6} 3s^{1}

Phosphorus K = 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{5}

Calcium Ca = 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 4s^{2}

## How difficult is quantum chemistry?

Quantum chemistry is the branch of chemistry that looks more abstract because it focuses more on the behavior and properties of smaller particles like electrons.

it is will be better to understand the basics and follow it step by step so we can easily grasp all the concepts.

## Quantum chemistry subtopics

The subtopics in quantum chemistry include thermodynamics, schrodinger vequation, molecular dynamics etc