Unit-8-Lesson-15-THE-CHEMICAL-BONDING.pptx

4
4-1
© 2006 Thomson Learning, Inc.
All rights reserved
Moles
At the end of the lesson, the students will
be able to :
1. describe the arrangement of elements in
the periodic table and trends in the
properties of elements in terms of
electronic structure
2. write the electron configurations of
elements
3. describe the quantum mechanics
4. identify scientist who contributed to the
development of quantum mechanics
5. use quantum numbers to describe an
electron
in an atom

4
4-2
© 2006 Thomson Learning, Inc.
All rights reserved
pp. 113 - 121
Lesson 15

Chemical
Formula
A is a shorthand representation of a
chemical compound or a molecule of an element. Thus;
There are three different types of chemical formulas.
These are :
NaCl for sodium chloride H2O for water
H2 for hydrogen molecule
Empirical formula
Molecular formula
Structural formula

Chemical
Formula
Molecular formula is used to represent compounds or
elements which exist as covalent molecules.
“Microscopic” interpretation
CO2 molecule composed of 1 carbon atoms
and
2 oxygen atoms
It shows the actual number of atoms of each element
present in a molecule of a compound or element.
Thus, the molecular formula for carbon dioxide is ;

Chemical
Formula
Structural formula is used for complex covalent
molecules such as those found in organic chemistry.
It shows not only the actual number of atoms of each
elements present , but also the arrangement of these
atoms in a molecule. Thus, the structural formula for
organic compound hexene and ethene are as follows;

Lewis Symbols
• Lewis symbol (Lewis structure) - a way to represent
atoms (and their bonds) using the element symbol and
valence electrons as dots.

• A covalent bond is formed by sharing one or
more pairs of electrons.
+
H H
the single line represents
a shared pairof electrons
.
. H H
• the pair of electrons is shared by both atoms
and, at the same time, fills the valence shell
of each atom.
• example: in forming H2, each hydrogen
contributes one electron to the single bond.

• Single bond - one pair of electrons are
shared between two atoms
Lewis Structure, Stability, Multiple
Bonds, and Bond Energies
H
-
H
or
H
:
H
N
N
or
..
N
..
N 


O
O
or
..
O
::
..
O 




• Double bond - two pairs of electrons are
• Triple bond - three pairs of electrons are

H
:
..
..
O
:
H
..
..
O
2H 




H
H
:
..
C
:
H
.
C
4H
H








Water = H2O
Methane gas = CH4

• An atom may or enough
electrons to acquire a filled valence shell
and become an ion. An ionic bond is the
result of the force of attraction between a
and an .
• An atom may with one or
more other atoms to acquire a filled
valence shell. A covalent bond is the
result of the force of attraction between
two atoms that share one or more pairs of
electrons.

• Ions are formed when the number of
protons and electrons in an atom are
not equal.
• Ions with more protons than electrons
are called cations.
• Ions with more electrons than protons
are called anions.

• An element and its ion have the same
chemical symbol, but different properties.
– Sodium metal reacts violently with water
– Ionic compounds containing sodium cation
dissolve in water.

• All bonds are created by the exchange
or sharing of electrons.
– The exchange or sharing of electrons
results in lower energy for the
compound relative to the separate
atoms.

• or is
formed when
electrons completely transfer from one
atom to
another by mutual attraction of
oppositely
charged ions.

• This emphasizes the
positions of the ions.
Green spheres are
chloride anions and
are
.
• This emphasizes the
relative sizes of the ions.
Green spheres are
chloride anions and
are
.

•
- electrons are usually shared in pairs
- 2,4, or 6 electrons are shared between two
nuclei, leading to an attraction between the
nuclei.

water H2O.
– Two electrons are shared between
each Hydrogen and the Oxygen atom.
carbon dioxide
CO2
Four electrons are shared between
each Oxygen and the Carbon atom.
propane
C3H8
– Two electrons are shared between
each set of bonding atoms.

Let’s examine the formation of NaCl
IONIC BONDS
Na+ + Cl- NaCl
Sodium has a
low ionization energy
it readily loses this
electron .
Na  Na+ + e-
Chlorine has a
high electron
affinity.
When chlorine
gains an electron,
it gains the Ar
configuration










 :
..
..
Cl
:
e
..
..
Cl
:
The forces of attraction of oppositely charged ions together
IONIC BONDING
The COMPLETE TRANSFER of electron from a METAL to a NON-METAL
Na
Atomic Number = 11
proton = 11
electron = 11
Cl
Atomic Number = 17
proton = 17
electron = 17
Na+
Cl-

Forming an Ionic Bond
• In forming sodium chloride, NaCl, one electron is
transferred from a sodium atom to a chlorine
atom:
• we use a single-headed curved arrow to show this
transfer of one electron:
Na + Cl Na+
Cl -
+
Na+
(1s2
2s2
2p6
)
Cl(1s2
2s2
2p6
3s2
3p5
)
+
Na(1s2
2s2
2p6
3s1
)
Cl-
(1s2
2s2
2p6
3s2
3p6
)
Sodium atom Chlorine atom
Sodium ion Chloride ion

Who donates and who accepts?
Ionic Bonding
“No“ Sharing of Electrons

Aim
1.“Ionic” Bonds
Li2,1
Na2,8,1
F2,7
[Li2]+
[Na2,8]+
[F2,8]-
+1e
-1e
-1e
Therefore:
Noble Gas Configuration
+ -
2 Na F
F2
2 Na +
Why Do Elements React ?

Covalent Bonding Sharing
Electrons

Covalent
Bonds
-4e
Shows only
valence e
(He) (Ne)
Compromise: electron-sharing
C
.
.
H
H
H
H
.
.
.
.
.
.
H O H
.
.
.
.
.
.
.
.
2. “Covalent” Bonds
C4+ +4e
C
C
2 H2 O2
+
4 H
+
C4-
Elements in the “middle” of the periodic table
have a problem with electron affinity (EA) and
ionization potential (IP):

Electronegativity
• Electronegativity : a measure an atom’s attraction
for the electrons it shares in a chemical bond
with another atom.
- -
Electronegativity increases
– on the Pauling scale, fluorine, the most
electronegative element is assigned a value of
4.0, and all other elements are assigned
values relative to fluorine.

Electronegativity
• Electronegativity Values of the Elements

Polarity of Covalent Bonds
• Although all covalent bonds involve sharing of electron
pairs, they differ in the degree of sharing:
Type ofBond
Less than 0.5
0.5 to 1.9
Greater than 1.9
Nonpolar covalent
Polar covalent
Ionic
Two nonmetals ora
nonmetal and a metalloid
Electronegativity
Difference Between
Bonded Atoms
A metal and a nonmetal
Most Likely to
FormBetween
• nonpolar covalent bond: electrons are shared equally
• polar covalent bond: electron sharing is not equal
the degree of sharing depends on the relative
electronegativities of the bonded atoms.

H-Cl
Bond
Difference in
Electronegativity Type of Bond
3.5 - 2.1 = 1.4
3.0 - 2.1 = 0.9
4.0 - 0.9 = 3.1
2.5 - 1.2 = 1.3
polar covalent
polar covalent
ionic
polar covalent
2.5 - 2.5 = 0.0 nonpolar covalent
3.0 - 2.1 = 0.9 polar covalent
O-H
N-H
Na-F
C-Mg
C-S
If EV value is : < 0.5 = non polar
0.5 -1.6 or 1.9 = polar
> 1.6 or 1.9 = ionic
Except :
NaI = ionic
HF = polar

Polarity of Covalent Bonds
• Examples:
H-Cl
Bond
Difference in
Electronegativity Type of Bond
3.5 - 2.1 = 1.4
3.0 - 2.1 = 0.9
4.0 - 0.9 = 3.1
2.5 - 1.2 = 1.3
polar covalent
polar covalent
ionic
polar covalent
2.5 - 2.5 = 0.0 nonpolar covalent
3.0 - 2.1 = 0.9 polar covalent
O-H
N-H
Na-F
C-Mg
C-S

HCl= 3.0- 2.1 = 0.9 = covalent
polar
HBr= 2.8- 2.1 = 0.7 = covalent
polar
HI = 2.5- 2.1 = 0.4 = covalent
non-polar
HF = 4.0- 2.1 = 1.9= ionic
0.5 -1.6 = polar
> 1.6 = ionic
= polar

NaF = 4.0- 0.9 = 3.1 = ionic
NaBr = 2.8- 0.9 = 1.9 = ionic
NaCl = 3.0- 0.9 = 2.1 = ionic
NaI = 2.5- 0.9 = 1.6= polar
0.5 -1.6 = polar
> 1.6 = ionic
= ionic

Predict what type of bond is formed from the following;
(a) H - Cl
(b) C - S
(c) Na - l
(d) Na - F
(e) H - F
(a) 3.0 - 2.1 = 0.9 polar covalent
(b) 2.5 - 2.5 = 0.0 nonpolar covalent
(c)2.5 - 0.9 = 1.4 ionic
(d) 4.0 - 0.9 = 3.1 ionic
(e) 4.0 - 2.1 = 1.9 polar covalent

Unit-8-Lesson-15-THE-CHEMICAL-BONDING.pptx

Unit-8-Lesson-15-THE-CHEMICAL-BONDING.pptx

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