Review
Quantum Numbers
The Principal Quantum Number (n)
Values: 1, 2, 3, and so forth
Size and energy of the orbital. It defines energy level (shell).
The Angular Momentum Quantum Number (l)
Values: from 0 to (n - 1)
“Shape” of the orbitals. It defines energy sublevel (subshell).
Chemical Bonding
Pre AP Chemistry – Part 1 A
The Magnetic Quantum Number (ml )
Values:
The orientation of the orbital in space. It defines number of the orbital.
The Electron Spin Quantum Number (ms )
Values:
0
spinning direction
1
l = 1 (p orbitals)
l = 0 (s orbitals)
The boundary surface enclose 90%
total electron density in an orbital
3 orientations
These three p orbitals:
• identical in size, shape, and energy
• they differ only in orientation
“Spherical ”
2
Note There is no simple relation between the values of ml
and the x, y, and z directions
3
Energy of orbitals
l = 2 (d orbitals)
5 orientations
Practice List the values of n, l, and ml for orbitals in the 4d subshell.
Energy depends on both n and l
4
Aufbau principle
1s < 2s <2p <3s <3p <4s <3d <4p
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5
Hund’s Rule
“Fill up” electrons from low energy orbitals to high energy
orbitals.
The most stable arrangement of electrons in subshells is
the one with the greatest number of parallel spins.
1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p ……
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The Pauli Exclusion Principle
If two electrons in an atom should have the same n, l, and
ml values, then they must have different values of ms .
Practice An oxygen atom has a total of eight electrons.
Write the orbital diagram of an oxygen atom and write
the four quantum numbers for each of the eight
electrons in the ground state.
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9
1
Practice
Shorthand notation with noble gas core is abbreviated
electronic configurations use [noble gas]
e.g. for Sc,
Full electron configuration: 1s22s22p63s23p64s23d1
Shorthand notation with noble gas core: [Ar]4s23d1
Practice Write the electron configuration for the following elements.
10
2
11
Valence electrons are the outer shell electrons of an atom.
Chemical bond
Group
Atoms interact to form a chemical bond, only their outer
regions are in contact, only valence electrons participate
in chemical bonding.
Chemical bond between two oxygen atoms
e- configuration
# of valence e-
1A
ns1
1
2A
ns2
2
3A
ns2np1
3
4A
ns2np2
4
5A
ns2np3
5
6A
ns2np4
6
7A
ns2np5
7
8A
ns2np6
8
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Lewis dot symbol
Lewis dot symbol of ions
Each dot represents a valence electron.
elements
valence electron
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Lewis dot symbol
H
1
H
Be
2
Be
B
3
B
C
4
C
N
5
N
O
6
O
F
7
F
Cation:
Lewis dot symbol
Na+
Na+
Ca2+
Ca2+
Anion:
14
Cl-
Cl
S2-
S
-
2-
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Electronegativity(EN)
9.2 the ionic bond
Electronegativity is the ability of an atom to attract toward
itself the electrons in a chemical bond.
Page 372
9.4 the covalent bond
Page 379
Beryllium, the first member of Group 2A, forms mostly
covalent compounds.
relative value, no unit, e.g. electronegativity of O is 3.5.
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16
A difference of 1.8 units or more will give a compound
that is predominantly ionic.
The Electronegativities of Common Elements
Increasing electronegativity
Increasing electronegativity
e
Incr
•
elec
g
n
i
as
tiv
ega
n
o
tr
ity,
A
pt 8
e
c
ex
Because noble gas are very stable, they can hardly form ordinary
compounds, so 8A elements are exceptions in electronegativity trend.
• F has largest electronegativity among the elements.
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19
Lattice:
A regular pattern or lattice of alternating positive
and negative ions
Ionic compound
Lewis dot symbols
e.g.1
CaO
Ca
e.g.2
+
O
Ca2+ O
2-
Li2O
2 Li
e.g.3
+
O
2Li+
O
2-
Mg3N2
3 Mg + 2 N
3Mg2+ 2 N 3-
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Lattice energy can be determined by coulomb’s law.
Lattice Energy
Lattice energy (U) is the energy required to
completely separate one mole of a solid ionic
compound into gaseous ions.
F is attraction force
F=k
Q+Qr2
Q+ is the charge on the cation
Q- is the charge on the anion
Lattice energy + NaCl(s) → Na+(g) + Cl-(g)
r is the distance between the ions
→
For ionic compounds, larger charge, smaller radius,
greater attraction force between cation and anion,
greater lattice energy.
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23
Compare and explain lattice Energy
Practice
Practice
Compound
Lattice Energy(kJ/mol)
MgF2
2957
MgO
3938
F=k
Q+Qr2
Which of the following ionic compounds will have the largest lattice
energy: Al2O3, MgO, CaO. Explain your answer.
In blue: ionic size in pm
Explain why MgO has larger lattice energy than MgF2?
Because charge of O2- is larger than F-, the attraction force
between Mg2+ and O2- is stronger than that between Mg2+
and F-. So MgO has larger lattice energy.
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Covalent bond type:
Covalent bonds
• Covalent bond is generally formed between nonmetal and
nonmetal.
Because their electronegativity difference is small
between nonmetal atoms.
• Polar (covalent) bond, different nonmetal atoms
• Nonpolar (covalent) bond, same nonmetal atom.
Polar covalent bond
• Covalent bond is formed by sharing electrons between
two atoms.
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Shared electron density is not
evenly distributed, but greater
electron density around one of
them. e.g. HF
Nonpolar covalent bond
shared electron density is
evenly distributed. e.g. H2
27
Why should two atoms share electrons?
F
+
7e-
F F
F
F F
7e-
8e- 8e-
Page 380
Lewis structure
“Octet rule”
• An atom except hydrogen tends to form bonds until it is
surrounded by eight valence electrons.
• Hydrogen atom tend to be surrounded by 2 valence electrons
when forming bond.
or
F
F
Lewis structure is a representation of covalent bonding in
which shared electron pairs are shown either as lines or as
pairs of dots between two atoms, and lone pairs are shown as
pairs of dots on individual atoms.
Bonding pair/shared electron pair
lone pairs
lone pairs
Lone pairs are not involved in covalent bond formation
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Single bond – two atoms share one pairs of electrons
H
+
O +
H
H O H
2e- 8e-
or
2e-
H
O
H
single bonds
Double bond – two atoms share two pairs of electrons
O C O
or
O
C
O
double bonds
8e- 8e- 8e-
Triple bond – two atoms share three pairs of electrons
N N
8e-8e-
or
N
N
triple bond
Bond Lengths：
Bond strength/stability：
Triple bond < Double Bond < Single Bond
Triple bond > Double Bond > Single30Bond
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