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CHAPTER 6
Atoms & Electronic Structure
Modern Atomic Structure
Atoms consist of subatomic particles:
Particle
Charge
Mass (amu) Location
Proton
Positive
1.0073
Nucleus
Neutron
Neutral
1.0087
Nucleus
Electron
negative
5.486 x 10-4 Electron
cloud
Atomic Number
The number of protons in an atom of an element.



Each element has a different atomic number or
number of protons.
Each element has no charge.
Each element has the same number of electrons as
protons to keep neutral.
Quantum Mechanics



Bohr Model states that electrons circle around the
nucleus of an atom using the hydrogen atom.
Heisenberg's Uncertainty Principle – impossible to know
simultaneously the exact momentum and location of an
electron.
Schrodinger’s Wave Equation – electrons exhibit both
wave and particle behavior and the probability of the
electron location can be determined.
Atomic Orbitals
Probable location of an electron.
Quantum numbers are used to describe the orbital



n – principle quantum number- whole number 1,2,3 etc… explains the energy level.
l – second quantum number or angular momentum – positive
whole number from 0 to n-1 – defines the shape of orbital
m l - magnetic quantum number – number from l to –l – describes
the orientation of orbital in space
Shell – collection of orbitals with the same principle quantum
number (n).
Subshell – collection of orbitals with the same n and l.
Designated by a number and a letter.
Atomic Orbitals
n=whole number
 Number of subshells = n
 Shape of orbitals from 0 to l = n-1
 Number of orbitals in each subshell m l = 2 l + 1
Value of l
0
1
2
3
Letter used
s
p
d
f
Number of
orbitals
1
3
5
7
Orbitals Shapes


s orbitals – spherical in nature and as n gets larger the
orbital gets larger.
p orbitals – 3 p orbitals in the x, y, z direction on the
Cartesian coordinate system corresponding to
m l - as n increases the orbitals get larger.

d orbitals – 5 orbitals

f orbitals – 7 orbitals
n-principle
quantum
number-shell
Possible values
of l -subshells
Subshell
designation
Possible values
of ml
1
1
1s
0
2
0
1
2s
2p
0
-1,0,1 2px,2py,2pz
3
0
1
2
3s
3p
3d
0
-1,0,1
-2,-1,0,1,2,3
Orbitals
Example: For n=2,
 How many subshells?

What are the possible values of l ?

What are the shapes of the orbitals?
Orbitals
Example: If l = 1, what are the possible values of m l
and how many subshells?
Final Quantum Number
ms – spin magnetic quantum number – the spin of the
electron in its orbitals. Possible value of + ½ or -½.
Since the electron creates a magnetic field, 2 electrons in
the same orbital, spin in opposite directions.
Pauli exclusion principle – “no two electrons in an atom
can have the same set of four quantum numbers n, l, m l
and ms “
Electron Configuration
Distribution of electrons among orbitals.
Orbitals are filled in order of increasing energy with
no more than 2 electrons per orbital.
Type of
Orbital
s
p
d
f
Number of
Orbital's
1
3
5
7
Number of
Electrons
2
6
10
14
1s
1s
2s
2p
3s
3p
4s
3d
4p
5s
4d
5p
6s
5d
6p
7s
6d
7p
4f
5f
s-block elements
d-block elements
p-block elements
f-block elements
Electron Configuration
Example : Write the electron configuration for:

H

N

Ne

S

Mn
Condensed Electron Configuration
Core electrons – electrons in the inner-shell of an atom.
Valence electrons – electrons in the outer- shell available for a reaction.
Example : Write the electron configuration for:
Example : Write the Condensed electron configuration for:

N

S

Mn
Atomic Number
The number of protons in an atom of an element.



Each element has a different atomic number or
number of protons.
Each element has no charge.
Each element has the same number of electrons as
protons to keep neutral.
Mass Number
Since elements can have the same atomic number but
differ in number of neutrons and thus mass there
needs to be a way to identify the difference.
mass number = # protons + # neutrons
12
6
C
Isotopes
Elements having the same atomic number but different
mass number.
23
11
X
X=symbol of element
23=mass # (number of
protons and neutrons)
11=atomic #
Symbol
#protons
#electrons
#neutrons
12
6
C
6
6
6
13
6
C
6
6
7
14
6
C
6
6
8
Example

Write the symbol for Magnesium atom with a mass
number of 24. How many electrons, protons and
neutrons does it have?

Magnesium 25?

Magnesium 26?