# Quantum Mechanics to Electrons in Atoms

This article is part of the ChemHelp Tutoring Wiki |

This article is part of the PhysicsHelp Tutoring Wiki |

Quantum Mechanics employs the use of special number called quantum numbers. Each quantum number specifies something different about the orbitals and electrons

## Contents

## 4 Quantum Number

### 1. The Principle Quantum Number (n)

The fist quantum number is called the principle quantum number (n). It indicates the relative size of the atomic orbital

### 2. The Second Quantum number (l)

The second quantum number is called angular momentum quantum number. It is related to the shape of molecular orbital

### 3. The Third Quantum Number (m)

The third quantum number called the magnetic quantum number tells us the orientation in space of a given atomic orbita

### 4. Forth Quantum number

The forth quantum number is called number. It tells us the 2 possible electron spin ,either 1/2 or -1/2

### Electronic Configuration

1.The Pauli Exclusion Principle: No two electrons in the same atom can be described by the same set of four quantum number

2. The Aufbau principle: When filling orbitals, the lowest energy orbitals available are always filled fist. ("Aufbau" means a building or a construction in German.)

3. Hund's Rule : When orbitals of equal energy are being filled, the most stable configuration is the one with the maximum number of unpaired electrons with the same spin

### Bohr's Postulate

1. The hydrogen atom had only certain allowed energy level or stationary states.

2. As long as an electron moved in an allowed orbit or stationary state. The electron (and therefore the atom) did not radiate or absorb energy

3. The electron could only move from allowed orbit to another if it absorbed or emitted an amount of energy exactly equal to the energy difference between the two orbits

### Beyond Bohr

1. Particle behaves like waves: Bohr Assume that an atom had only certain allowed energy level in order to account for hydrogen's observed line spectrum. However, that assumption was not rooted in any physical theory. In other words, Bohr knew the theory is there but not way they had to be there. It appeared that the new theory containing some bold lines about atom might be needed.

2. De Brogli's Equation :For any moving particle, whether it is an electrons or baseball, has a wavelength that we can calculate. Particle's wavelength is inversely proportional to its mass; as the mass of the particle decreases, its wavelength increases and vice versa

3. Particle - Wave Duality: Electron can Behave like particle and wave

4. Heisenburg, Shrodinger's equation: Cannot detect both location and momentum of the electron at the same time.