Quantum Model of the Atom

Quantum Model of the Atom

defn: Heisenburg uncertainty principle: it is impossible to determine simultaneously both the position and velocity of an electron or any other particle.

defn: Quantum theory: this theory describes mathematically the wave properties of electrons and other small particles.

defn: Orbital: An orbital is a three dimensional region around the nucleus that indicates the probable location of an electron.

defn: Quantum numbers: specify the properties of atomic orbitals and the properties of electrons in an orbital.

There are four different quantum numbers:

1. Principle quantum number

2. Angular momentum quantum number

3. Magnetic quantum number

4. Spin quantum number

Each number describes a different aspect of the electron. Similar to an address

1. Country2. City3. Street4. House number

Principle Quantum#(n) Angular Momentum# (n-1)

1 0 s2 1 p3 2 d4 3 f

defn: Electron configuration: The arrangement of electrons in an atom.

1. Aufbau principle: Electrons enter orbitals of lowest energy first.

2. Pauli exclusion principle: An atomic orbital may describe at most two electrons. To occupy the same orbital, the two electrons must have opposite spins. (shown as arrows)

3. Hund’s rule: When electrons occupy orbitals of equal energy, one electron enters each orbital until all the orbitals contain one electron with parallel spins. Second electrons then add to each orbital so that their spins are opposite those of the first electrons.

Electron Configuration Rules

The electron configuration of an atom is a shorthand method of writing the location of electrons by sublevel.

The sublevel is written followed by a superscript with the number of electrons in the sublevel. If the 2p sublevel contains 2 electrons, it is written 2p2

Electron Configurations

We can use the periodic table to predict which sublevel is being filled by a particular element.

Blocks and Sublevels

Aufbau Diagrams: useful when remembering the order in which orbitals fill

Electron Configurations Electron Configurations and the Periodic Tableand the Periodic Table

• The periodic table can be used as a guide for electron configurations.

• The period number is the value of n.• Groups 1A and 2A have the s-orbital filled.• Groups 3A - 8A have the p-orbital filled.• Groups 3B - 2B have the d-orbital filled.• The lanthanides and actinides have the f-orbital filled.

Aufbau Principle: Fill orbital of lowest energy first.Pauli’s Exclusion Principle: No more than 2 electrons/orbital, spins oppositeHund’s Rule: Fill orbitals of equal energy with single electrons (spins parallel) before doubling.

Element 1s 2s 2px 2py 2pz 3s Electron configuration

1H

2He

3Li

4Be

5B

6C

7N

8O

9F

10Ne

11Na