Covalent bonding Covalent bond: A chemical bond formed when two atoms share electrons.
Chapter9 Covalent BondingCovalent bonding involves sharing of electrons to achieve noble gas...
Transcript of Chapter9 Covalent BondingCovalent bonding involves sharing of electrons to achieve noble gas...
Chapter 9
� Valence electron
� Covalent bonding
� Single, double and triple bonds
� Bonding electrons and Non-bonding electrons (lone pair of electrons)
�Bond energy and bond length
�Electronegativity
Keywords:
Covalent Bonding
Chapter 9
Ionic Versus Covalent Bonding
� Ionic compounds are formed when electrons are
transferred from one atom to another
�The transfer of electrons forms ions
�Each ion is isoelectronic with a noble gas
�Electrostatic force (ionic bond) holds atoms together
� Covalent bonding involves sharing of electrons to achieve noble gas configurations for the atoms
involved
�Covalent bond = attractive force resulting from atoms attracted to a shared pair of electrons
Chapter 9
Covalent Bonding� First, some background
�The octet rule: The atoms tend to gain, lose or share electrons to have eight electrons in the valence shells (electronic configuration of noble gas, stable configuration)
�Carbon (group IVA) would need to gain or lose 4 electrons to achieve noble gas configuration in an ionic compound
�Diatomic molecules, like O2, Cl2, I2 do not transfer electrons to form ionic bonds
�Cl- ⇔ Cl+ ???? Does this look OK?
Chapter 9
Covalent Bonding – H2
� Another type of bonding is at work here
� G. N. Lewis (1916) theorized that noble gas configurations could be attained by “electron sharing”
For H2(a) Two noninteracting H atoms,
each with one electron in its
1s orbital
(b) As the two H atoms approach,
the spins pair and the s
orbitals merge into a molecular
orbital, electrons are shared
(c) Fully formed molecular orbital
(d) Each H atom is “satisfied”
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Formation of Covalent BondChapter 9
Distribution of electron density in H2
�Electron density is highest around and
between the nuclei.
Chapter 9
Covalent Bonding – Cl2
� Each Cl atom has a 3p orbital that is singly occupied
� Bonding pairs
� Lone pairs
� Check the octets!
3p ↑↓ ↑↓ ↑
3s ↑↓
2p ↑↓ ↑↓ ↑↓
2s ↑↓
Cl 1s ↑↓
C l..
..: . Cl
..
.. :Cl..
.. :.
+ Cl..
..: ..
Chapter 9
Multiple Covalent Bonds
� Each Cl atom in Cl2 achieves its octet with a single Cl-Clbond
� What about N?
� How can nitrogen satisfy its octet?
� Which bond is stronger, that in Cl2 or in N2?
N..
.. . N
..
.. . N
..
.. . N
..
.. .+
Cl..
.. :Cl..
..: .. Cl..
.. :Cl..
..:or
Chapter 9
Types of Bond and Bond Order
Types of bond Bond order
Single (Cl2, HCl) 1
Double (O2) 2
Triple (N2) 3
� Bonding pairs and lone pairs
Cl..
.. :Cl..
..: ..
Bonding pairs
Lone pairs
Chapter 9
Bond energy and bond length
� Bond formation: exothermic process, -E
� Bond breakage: endothermic process, +E
� Bond length: distance between the nuclei between two bonded atoms
Chapter 9
Electronegativity and Bond Polarity
� Electronegativity
A measure of the ability of an atom in a molecule to draw electrons to itself.
-An atom with large negative electron affinity and large ionization energy has large electronegativity.
Example: fluorine, oxygen
Chapter 9
i) Both men are equally strongii) Both men are equally weak
iii) One is stronger than the other
No one will win
The stronger will win
Electronegativity and Bond Polarity
Chapter 9
Electronegativity Scale
Decreases
Increases
Chapter 9
Electronegativity and Atomic Size
�Electronegativity is inversely related to atomic size.
Chapter 9
Electronegativity and bond polarity
> 2.0
0.5 -2.0
< 0.5
Chapter 9
�Bond polarity increase as the value of ∆χ increase
�∆χ : difference in electronegativity values between thebonded atoms
∆χH2 0.0 non-polar covalent (∆χ = 0)
HF 1.8 polar covalent (0 <∆χ <2.0)
LF 3.0 ionic (∆χ >2.0)
�Bond polarity order for hydrogen halides:
HF (∆χ = 1.8) > HCl (∆χ = 1.0) > HBr (∆χ = 0.8) > HI (∆χ = 0.5)
Bond Polarity and Electronegativity
Chapter 9
Bond Polarity
� Use electronegativity values to classify the bonding
in the following molecules (ionic, polar covalent, or nonpolar covalent)
� KF
� NO
� SiCl4
� K2O
Chapter 9
Naming Covalent Molecules
� General rules
� Make sure the compound qualifies as a covalent molecule (and not ionic)
� Give the name of the least electronegative element first
� Give the stem name of the more electronegative element, ending with “ide”
� Indicate the number of each type of atom by the prefixes, mono, di, tri, tetra, penta, etc.
� PCl5 phosphorus pentachloride
� SO2 sulfur dioxide
� N2O dinitrogen monoxide
� CO carbon monoxide
� CO2 carbon dioxide
Chapter 9
Naming Covalent Molecules
� CCl4
� NO
� SeF4
� S2O7
� CaCl2
� N2O4
Chapter 9
Naming Covalent Molecules
� Diphosphorus pentoxide
� Sulfur trioxide
� Silicon tetrachloride
� Trihydrogen nitride
� Dihydrogen monoxide