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The Quantum Mechanical Model
The nucleus is found inside a blurry “electron cloud” A area where there is a high probability of finding an electron.

*No more than 2 electrons in each orbital*
Electron Configuration Principal Quantum Number (n) = the energy level of the electron. (max # e- = 2n2 ) Sublevels- like theater seats arranged in sections (s,p,d,f) (# of sublevels = n ) Within each energy level, the complex math of Schrodinger’s equation describes several shapes. These are called atomic orbitals - regions where there is a high probability of finding an electron *No more than 2 electrons in each orbital*

Summary # of orbitals Max electrons Starts at energy level sublevel s
1 2 1 p 3 6 2 d 5 10 3 7 14 4 f

Relative sizes of the spherical 1s, 2s, and 3s orbitals of hydrogen.

Diagram of principal energy levels 1 and 2.

The shapes and labels of the five 3d orbitals.

Electron Configurations
The way electrons are arranged in atoms. Three main “guiding” principles: Aufbau principle- electrons enter the lowest energy first.

Electron Configurations
Pauli Exclusion Principle- at most 2 electrons per orbital Why only 2 electrons per orbital? like charges repel each other, but… electrons spin on axis, clockwise or counterclockwise, creating magnetic polarization ( ↑↓ )

Hund’s Rule- When electrons occupy orbitals of equal energy (same sublevel ) they don’t pair up until they have to. - one electron enters each orbital until all orbitals contain one electron with spins parallel.

Writing Electron Configurations
(Letter - number designation) # of e- H 1s1 Sublevel Principle Energy Level

Orbital Diagrams ↑ ↓ ↑ ↓ ↑ ↑ ↑ N 1s 2s 2p 2 2 3
Show each orbital as a circle, box, or line. Show each electron as an arrow, ↑ or ↓ spin. Label electron configuration (letter –number). N 7 1s 2s 2p 2 2 3

Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p 3s 2p
Orbital (Aufbau) diagram

Example Let’s determine the electron configuration & orbital diagram for Phosphorus Need to account for 15 electrons

Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p 3s 2p

Orbitals being filled for elements in various parts of the periodic table.

Remember… When we write electron configurations, we are writing the lowest energy (ground state) configuration. Do Problems pg 160 *** # 21 draw orbital diagrams, not just e- configurations

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