Transcript Electrons in the Atom

Electron Configuration
Topic #8
September 2012
How was the Atomic Model
developed?
 The first modern atomic theory, proposed by
Dalton, portrayed the atom as a solid indivisible
mass.
 After the discovery of the electron by J. J.
Thomson, the atomic model was revised to
include them. J. J. Thomson’s model is referred
to as the “plum-pudding” model.
 Rutherford pictured the atom as a dense
nucleus surrounded by electrons.
 In the Bohr model, the electrons move in circular
paths.
 The quantum mechanical model is the modern
description of the electrons in atoms. This
model estimates the probability of finding an
electron within a certain volume of space
surrounding the nucleus.
Schrodinger
What are Atomic Orbitals?
Atomic orbitals are
regions around the nucleus
within which the electrons
have the highest
probability of being found.
Energy levels are regions
in space around the
nucleus where an electron
is likely to be moving.
How are Electrons Arranged in an Atom?
 The ways in which electrons are
arranged around the nuclei of atoms are
called electron configurations.
 It is also the most stable arrangement of
electrons around the nucleus of an atom.
General Patterns of Filling Orbitals
How are Electron Configurations for
Atoms written?
Rules that govern Electron Configuration:
1. Aufbau principle
Electrons enter orbitals of lowest energy first.
2. Hund’s rule
When electrons occupy orbitals of equal
energy, one electron enters each orbital until
all the orbitals contain one electron with
parallel spin.
3. Pauli exclusion principle
An atomic orbital may describe at most two
electrons.
General Patterns of Filling Orbitals
Let’s Practice!
Write the electron configuration for the
following atoms:
1.C
2.S
3.K
4.Ar
1s2 2s2 2p2
1s2 2s2 2p6 3s2 3p4
1s2 2s2 2p6 3s2 3p6 4s1
1s2 2s2 2p6 3s2 3p6
Let’s Practice!
Which atoms are these?
1. 1s2 2s2 2p4
2. 1s2 2s2 2p6 3s2 3p2
3. 1s2 2s2 2p6 3s2 3p6 4s2
4. 1s2 2s2 2p6 3s2 3p5
1.O
2.Si
3.Ca
4.Cl
Noble Gas Notation for Electron
Configuration
You do not have to repeat yourself over and over
1. Oxygen 1s2 2s2 2p4
[He] 2s2 2p4
2. Silicon 1s2 2s2 2p6 3s2 3p2
[Ne] 3s2 3p2
3. Calcium 1s2 2s2 2p6 3s2 3p6 4s2
[Ar] 4s2
4. Chlorine 1s2 2s2 2p6 3s2 3p5
[Ne] 3s2 3p5
Your turn.
Give both the expanded electron notation
and the noble gas notation on blank page
of notes.
Nitrogen
Argon
Titanium
Selenium
Strontium
Fluorine
References
Wilbraham, Antony C., Dennis C. Staley,
Michael S. Matta, and Edward L.
Waterman. Chemistry. New Jersey:
Prentice Hall, 2002.
Summary of Principal Energy Levels,
Sublevels, and Orbitals
Principal
Energy Level
Number of
Sublevels
Type of Sublevel
n=1
1
1s (1 orbital)
n=2
2
2s (1 orbital) 2p (3 orbitals)
n=3
3
3s (1 orbital) 3p (3 orbitals) 3d (5 orbitals)
n=4
4
4s (1 orbital) 4p (3 orbitals)
4d (5 orbitals) 4f (7 orbitals)