Chemistry Grade 11 Unit 3: By: Addis Ababa Education Bureau APRIL 2020
Chemistry Grade 11 Unit 3: By: Addis Ababa Education Bureau APRIL 2020
Chemistry Grade 11 Unit 3: By: Addis Ababa Education Bureau APRIL 2020
UNIT 3
two atoms.
- A compound that contain covalent bond
is
called covalent compounds
Examples of covalent compounds are:
H2O, NH3, CO2, CS2, SiCl4, CH4, C2H6,
CF4 , ….
The representation of covalent bonding
through Lewis symbols and shared
Coordinate covalent bonding
-Is a bond in which both
shared electrons are
donated
by only one atom .
Examples: O3, CO,
NH3BF3,
H3O , NH4 ,
+ +
…
Resonance structures
-Are a molecule or ion that can be
represented by two or more
Lewis
structures.
-Differ only in the distribution of
electrons
Examples: O3, N2O4, HNO3,
NO2F, NO3-,
CO32-, …
Exceptions to the octet rule in
covalent bonding
Three groups of molecules that are
exceptions to the Octet rule
Less than Octet
More than octet
Odd number of total valence electrons
Properties of Covalent Compounds
Covalent compounds are
-Molecular substances
-Have low melting and boiling points
-Volatile because many covalent compounds are found in
gaseous state at room temperature.
-Generally insoluble in water
Molecular Geometry
-The spatial arrangement of atoms around a central atom of
a
molecule or a poly atomic molecule.
- Valence shell electron pair repulsion (VSEPR) theory
predicting
the shapes of molecules and ions.
-The general formula for predicting molecular shapes is
Intermolecular Forces in covalent compounds
Intermolecular forces
- Force of attraction between atoms or molecules
- Affect the physical properties of the species
- Not chemical bonds
- Relatively weak
The common intermolecular forces are
London force
dipole- dipole force
H-bonding
3. METALLIC BONDING
-Is formed by the force of attraction between freely moving
electrons
and metallic nuclei.
-Is referred to as bonding in metal atoms.
-the strength of metallic bonding depends on the number of
contribution electrons and size of the atoms.
Examples: Na , K , Li , Cs , Mg , Be, Ca , Fe, Cu , Co, W, Zn, Al,
………..
Properties of Metals
• A high degree of electrical conductivity
• A high degree of thermal conductivity
• luster(shiny)
• High density
• Malleable and ductile
• High melting and boiling point
Chemical Bonding Theories
The two modern chemical bonding theories are
Valence Bond Theory (VBT) and Molecular
Orbital Theory (MOT)
1 - Valence Bond Theory (VBT)
explains the bonding between two atoms
caused
by the overlap of half-filled atomic orbitals.
Overlap of Atomic orbitals (Sigma and pi bonds).
The three simple types of overlaps are:-
I. S-S
II. S-P
III. P-P
Hybridization of orbitals
Hybridization is mixing up of two or
more different atomic
1-Ionic crystals
-the fundamental units are ions.
- consist of cations and anions held
together by electrical attraction of opposite
charges.
Example: NaCl , KNO3 ,CaCO3,…
2-Molecular crystals
- the fundamental unit of a molecular solid is molecule
- consist of atoms or molecules held together by
intermolecular forces.
-non conductors of heat and electricity.
Example: sugar, dry ice , glucose , aspirin,….
3-Covalent network crystals
-the fundamental units are atoms.
-consist of atoms held together in large
networks
by covalent bonds.
-The whole is one giant molecule .
Example: quartz(SiO2), diamond , graphite,
4-Metallic crystals
- the fundamental units are atoms.
- consist of atoms held together by metallic
bonding.
- conduct heat and electricity