Transcript SCH3U Chemical Bonding

SCH3U Chemical
Bonding
Ionic vs. Covalent Compounds
Ms. Yusuf
Formation of Bonds
Chemical Bonds are formed between two atoms
using shared valence electrons; this is the force
that holds atoms together in compounds.
Valence Electrons are the electrons that
occupies the outermost energy level of an atom
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Type of Bonds
Ionic vs. Covalent
 Ionic bonding occurs between metals and non-metals
 Covalent bonding occurs between non-metals
Note: Bonding between metals is called Metallic bonding

Video Clip: Chemical Bonding
Octet Rule
Most Noble gasses have 8 electrons in their outer shell.
This is a stable conformation. Thus, the noble gasses do
not react with other elements. In other words, noble
gasses are very stable.
Octet Rule (Continued)
When atoms form ions or combine in compounds
they obtain electron configurations of the nearest
noble gas (eight electrons in their valence shells)
Ionic Bonding
Ionic Bonds are formed from the electrostatic
attraction of positive and negative ions
An atom that can
lose an electron to
become a positively
charged ion, called
a cation
An atom can gain
electrons to become
a negatively charged
ion, called an anion
•In each case, the atom attains a noble gas configuration with
its valence electrons.
•A noble gas configuration is defined as a completely filled
outer shell, like the noble gases.
Ionic Bond: Example (Na and Cl)
Ionic Bond:
Example
(Al and O)
Al
O
O
Al
O
Examples of Ionic Bonding
using Lewis Structures

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Magnesium and Fluorine
Calcium and Oxygen
Potassium and Sulfur
Covalent Bonding
Covalent bonding occurs between two non-metals. Covalent bonding is
different from ionic bonding because electrons are shared instead of
transferred.
Each atom has eight shared electrons
Covalent Bonding: Example (H
and F)
H
F
HF
Covalent Bonding Using Lewis
Structures

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Silicon Oxygen
Hydrogen and chlorine
Bromine and Bromine
Elements will not share the electrons in a bond
equally
•The electronegativity (EN) of an element determines its
ability to attract electrons in a bond
•When elements are bonded together, the more
electronegative element attracts the electrons
Example: HF
•Flourine is more electronegative.
•The electrons in the bond are attracted towards the fluorine atom
Polar Bond (Dipole Moment)
ENF = 4.0
ENH = 2.1
∆EN H-F = 4.0 - 2.1 = 1.9
(Continued)

This is not a complete transfer of an electron from hydrogen to
fluorine; it is merely a drifting of electrons toward fluorine
H F Cl Cl
:
Polar Covalent

:
Covalent
When a charge separation of this type is present, the molecule
possesses an electric dipole, so called “dipole moment” and the bond
is called a POLAR COVALENT BOND
Polar Covalent Compound

0.5 < Electronegativity difference < 1.7

This difference is great enough for the
bonding electron pair to spend more time
near the more electronegative atom than
the less electronegative atom.
(Continued)
-
O
Example: Water (H2O)
∆EN = 1.24 (which is between 0.5 and 1.7)
H
H
Polar Covalent Bond
+
+
Oxygen = a slightly negative charge
Hydrogen = a slightly positive charge
Since the hydrogen does not completely transfer its
electron to the oxygen, the their respective charges
are indicated as  + (the indication of partial positive
charge) and  - (indication of partial Negative
charge).

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Comparison of Ionic, Nonpolar covalent and Polar
covalent bonding
3.3
1.7
[Na]+[Cl]-
0.5
H+ - Cl-
0
Cl - Cl
∆EN
Summary
Chemical Bonds are formed between the atoms in
molecules
The bonds are formed from the valence electrons of the
atoms and the resulting bond allows each atom to achieve a
noble gas configuration (the most stable arrangement of
electrons around the atom: Octet Rule)
The types of bonding can be classified as:

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1.
2.
3.
Covalent (non-metal bondin; 0<∆EN<0.5)
Polar covalent bonds (non-metal bonding with a dipole
moment; 0.5<∆EN<1.7)
Ionic (metals + non-metals; 1.7 <∆EN< 3.3)
Questions

Complete the chart:

Identify each compounds as ionic or covalent: CCl4,HCI, MgF2,
H2O,NH3, NaCl, OH, H2
Show how the bond forms between Li+Cl, Mg +O (Follow the Octet
Rule) as well as Li + O
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