Chapter6
Chemical Bonding
Dr.Essam Saber Abd El-Sayed Ahmed
Chemical Bonding
• Chemical bonds: are the attraction between atoms that hold
compounds together.
• Chemical bonds divided by two categories:
ionic bonds .
Covalent bonds.
Bonding in ionic compounds
• Ionic compound: is a compound consisting of cations and anions held
together by electrostatic attraction into crystal structure
for example : LiF , NaCl , CaO ,CaCl2 , Li2O…
Na (1S2 2S2 3S1 )
Na+ (1S2 2S2 2P6 3S0)+eCl ( 1S2 2S2 2P6 3S2 3P5)+eCl- (1S2 2S2 2P6 3S2 3P6)
Na+ +clNa+cl-
Factors
• Law ionization energy and high electron affinity
• The lattice energy of the resulting compound is very large
• Two factor (1)+(2).
According to the above factors most compounds
formed between metals and non metals are ionic
Lewis symbols
• Lewis symbols are used to describe valence electron
configurations of atoms and non-atomic ions. These symbols
consist of the symbol for the element and one dot each valence
electron present . When two dots written adjacent to each
other , as in
The covalent bond:
The covalent bond is a bond formed between two atoms
by electrons sharing . In a single bond , one electron pair
is shared . Double and triple covalent bonds are called
multiple bonds. In a double bond , two electron pairs are
shared , and in a triple bond , three electron pairs are
shared
For example:
Single bond :
• Double bond:
• Triple bond:
The covalent bond
Note that, the atoms in polyatomic ions, such as
OH- , NO3- and NH4+ are held together by
covalent bonds.
Thus , compounds containing polyatomic ions are
stabilized by both covalent bonds and ionic
bonds . For example KNO3 has ionic bonds
resulting from the electrostatic attraction
between ions K+ and NO3- and covalent bonds
between the nitrogen and oxygen atoms in NO3-.
Lewis structures:
• Lewis structures:
Lewis structures utilize Lewis symbols to show electrons in molecules
and ions For example :
Lewis structures shown above for Cl2 indicates that Cl atom has three
pairs of electrons that are not used in bonding (called unshared
pairs , or lone pairs) and one shared pair of electrons.
OCTET RULE
The tendency of the ions of many of the representative
elements to have a noble gas configuration with 8 electrons
in the outer shell , is the basis of the Octet rule . When metals
and non metals of A groups react they often tend to gain or
lose electrons until there are eight electrons in the outer shell
The central atoms in the following example obey octet rule.
Bond order and some bond
properties :
Bond order : is the number of covalent bonds that exist
between a pair of atoms
Some bond properties :
1- Average bond length : the bond length decreases as the
bond order increases
2-Average bond energy : the bond energy increases as the
bond order increases
3- Average vibrational frequency : for a given pair of
atoms , as the bond order increases . So dose the
vibrational frequency .
Multiple choice –questions:
1.Which of the following compounds dose not obey the octet rule:
1) PCl3
a)1,2
2) PCl5
b)2,4
3) SF6
c)1.3
4) CCl4
d)2.3
2. Which of the compounds , the central atom dose not obey the octet rule:
a)PCl3
b) H2o
c) IF7
d) CCl4
3.Consider the following compounds:
The largest carbon – nitrogen vibrational frequency is:
a)
b)
c)
d)
4.The c-c bond order , bond length and bond energy in the following
compounds H3C-CH3 , H2C= CH2 and HC = CH are respectively :
bond order
bond length
bond energy
A) Increases
Increases
decreases
b) Increases
decreases
Increases
c) Increases
Increases
decreases
d) Decreases
Increases
Increases
5. In one of the following compounds, the central atom obeys the octet
rule:
a) PCl5
b) ClF3
c) IF-4
d) PF3
6. One of the following statement is incorrect:
a)The largest the bond order the stronger the bond
b) The weaker the bond the smaller the vibrational
frequency
c) The shorter the bond the smaller the bond order
d) The higher the vibrational frequency the stronger the bond
7. The value of bond energy is an indication of:
1) Bond strength 2) bond length
a) 1,3
b)1,2
3) polarity
c)2,3
4) solubility
d)3,4
8. Which of the following increase(s) by increasing bond order:
1)Bond length
3)Bond energy
a)1,2
2)vibrational frequency
4) non of the above
c)1,3
d)3,4
b)2,3
9. Which of the following compounds do(es) not obey octet rule:
1)NaF
a)1,2
2) PF5
b)2,3
3) CCl4
c)3,4
4) CO2
d)2
10.In one if the following , the central atom(s) do(es) not obey octet rule:
1) H3O+
a)1,2
2) NH4+
b)3
3) SCl4
c)2
4) PF5
d)3,4
11. The type of bond between two similar non-metallic atom is:
a) A pure ionic bond
b) A pure covalent bond
c) 50% ionic and 50% covalent
d) No bond is formed
12. The factors that lead to ionic bond formation are:
a) High ionization energy and low electron affinity
b) High ionization energy and high electron affinity
c) High ionization energy only
d) Low ionization energy and high electron affinity