Download Ch.4-Electron Arrangement in Atoms

ARRANGEMENT OF ELECTRONS IN ATOMS
Chapter 4
Chemistry
The Quantum Model of the Atom
Electrons as Waves
In 1926, Erwin Schrodinger used the hypothesis that electrons have a duel
wave-particle nature to develop an equation that treated electrons in atoms
as waves.
From this, Schrodinger developed the Quantum Theory.
The Quantum Theory describes mathematically the wave properties of
electrons and other very small particles.
The Quantum Model of the Atom
Electrons as Waves
From Schrodinger’s findings, he was able to determine that electrons do not
exist in defined orbits, but in regions around the nucleus.
The regions around the nucleus came to be known as orbitals.
Orbitals are three-dimensional regions around the nucleus that indicate
the probable location of an electron.
The Quantum Model of the Atom
Electron Cloud
The Quantum Model of the Atom
Atomic Orbitals and Quantum Numbers
Wave Mechanical Model
Today’s atomic model is based on the
principles of wave mechanics.
According to the theory of wave mechanics,
electrons do not move about an atom in a
definite path, like the planets around the sun.
Erwin Schrodinger used the results from new
experiments to present a new, mathematicallybased model.
The Quantum Model of the Atom
Atomic Orbitals and Quantum Numbers
Wave Mechanical Model
In Schodinger’s new theory, he stated that it
was impossible to determine the exact
location of an electron.
The probable location of an electron is
based on how much energy the electron
has.
This is represented in an Electron Cloud
Diagram.
The Quantum Model of the Atom
Electron Cloud
The electron cloud is a space in which electrons are likely to be found.
Electrons whirl about the nucleus billions of times in one second.
roughly the speed of light
They are moving around in random patterns.
The location of electrons depends upon how much energy they have.
Electrons with the lowest energy are found in the energy levels closest
to the nucleus.
Electrons with the highest energy are found in the outermost energy
levels, farther from the nucleus.
The Quantum Model of the Atom
Quantum Numbers
Quantum numbers specify the properties
of atomic orbitals and the properties of
electrons in orbitals.
There are four quantum numbers.
Principal
Angular Momentum
Magnetic
Spin
The Quantum Model of the Atom
Quantum Numbers
Principal Quantum Number
The principal quantum number, symbolized by n, indicates the main energy
level occupied by the electron.
range from 1 to 7
The higher the energy level, the further away from the nucleus they are.
The Quantum Model of the Atom
Quantum Numbers
Principal Quantum Number
The Quantum Model of the Atom
Quantum Numbers
Principal Quantum Number
The energy level indicates the
size of the electron cloud.
The formula 2n2 indicates the
total possible electrons in an
energy level.
The Quantum Model of the Atom
Quantum Numbers
Principal Quantum Number
Example
Calculate the total possible electrons in the 1st through 4th energy levels.
Remember 2n2.
Energy Level
Number of Electrons
1
2
2
8
3
18
4
32
The Quantum Model of the Atom
Quantum Numbers
Angular Momentum Quantum Number
The angular momentum quantum
number or orbital quantum
number, symbolized by l,
indicates the shape of the orbital.
The Quantum Model of the Atom
Quantum Numbers
Angular Momentum Quantum Number
An orbital is a three-dimensional region
around the nucleus that indicates the
probable location of one pair of
electrons.
The orbitals are s, p, d, and f.
This indicates the shape.
s
p
d
d
The Quantum Model of the Atom
Quantum Numbers
Angular Momentum Quantum Number
The s-orbital is sphere shaped.
The Quantum Model of the Atom
Quantum Numbers
Angular Momentum Quantum Number
The p-orbital is dumb bell
shaped.
The Quantum Model of the Atom
Quantum Numbers
Angular Momentum Quantum Number
The d-orbital is clover
shaped.
The Quantum Model of the Atom
Quantum Numbers
Angular Momentum Quantum Number
The f-orbital is flower
shaped.
The Quantum Model of the Atom
Quantum Numbers
Magnetic Quantum Number
The magnetic quantum number, symbolized by m, indicates the orientation
of an orbital around the nucleus.
Since the s-orbital is spherical, it can
have only 1 orientation.
The Quantum Model of the Atom
Quantum Numbers
Magnetic Quantum Number
The p-orbital has 3 possible orientations.
The Quantum Model of the Atom
Quantum Numbers
Magnetic Quantum Number
The d-orbital has 5 possible orientations.
The Quantum Model of the Atom
Quantum Numbers
Magnetic Quantum Number
The f-orbital has 7 possible orientations.
The Quantum Model of the Atom
Quantum Numbers
Spin Quantum Number
The spin quantum number
has only two possible values +½ or -½ - which indicates the
two fundamental spin states
of an electron in an orbital.
Electron Configuration
Electron Configuration
Stability
Electrons are arranged in the most stable way possible, in the lowest-energy
level available.
Electron Configuration
Electron Configuration
The arrangement of electrons in an atom is know as the atom’s electron
configuration.
The lowest-energy arrangement of the electrons for each element is called
the elements’s ground-state electron configuration.
The order of increasing energy for atomic sub levels is shown
on the vertical axis. Each individual box represents an orbital.
Electron Configuration
Rules Governing Electron Configuration
According to the Aufbau principle, an electron occupies the lowest-energy
orbital that can receive it.
According to the Pauli exclusion principle, no two electrons in the same
atom can have the same set of four quantum numbers.
According to Hund’s rule, orbitals of equal energy are each occupied by one
electron before any orbital is occupied by a second electron, and all
electrons in singularly occupied orbitals must have the same spin state.
Electron Configuration
Representing Electron Configuration
Orbital Notation
An unoccupied orbital is represented by a line, with the orbital’s name
written underneath the line.
1s
An orbital containing one electron is represented as:
1s
An orbital containing two electrons is represented as:
1s
Electron Configuration
Representing Electron Configuration
Electron Configuration Notation
Electron configuration notation eliminates the lines and arrows of orbital
notation.
Contains 3 items:
Number represents the energy
level
Letter represents the sub level
Superscript represents the
number of electrons
2
1s
Electron Configuration
Representing Electron Configuration
Sample Problem A
The electron configuration of boron is 1s2 2s2 2p1. How many electrons are
present in an atom of boron? What is the atomic number of boron? Write
the orbital notation for boron.
2
2
1
1s 2s 2 p
Electron Configuration
Representing Electron Configuration
Sample Problem B
Write the orbital notation for oxygen. What is the electron configuration
for oxygen?
2
2
1s 2s 2 p
4
Electron Configuration
Representing Electron Configuration
Sample Problem C
Write the orbital notation for chlorine. What is the electron configuration
for chlorine?
2
2
6
2
1s 2s 2 p 3s 3p
5
Electron Configuration
Representing Electron Configuration
Sample Problem C
Write the orbital notation for calcium. What is the electron configuration
for calcium?
2
2
6
2
6
1s 2s 2 p 3s 3p 4s
2
Electron Configuration
Representing Electron Configuration
Sample Problem E
Write the orbital notation for iron. What is the electron configuration for
iron?
2
2
6
2
6
2
1s 2s 2 p 3s 3p 4s 3d
6