CHEMICAL
BONDING
Atoms are very active because of their high energy. They have
tendency to be more stable and carry less energy through
combination together to give molecules.
Molecules are more stable and have less energy than atoms.
Atoms join together through chemical bonding.
Non-metal------------- Non-metal
Chemical bonding may be formed between atoms of two
nonmetals similar or different by sharing electrons to
complete the outermost shell of each one to the electronic
configuration of the nearest inert gas thus can acquire a
stable, Nobel-gas structure (Lewis suggestion).
Metal-------Non-metal
Chemical bonding may also be formed between a metal and
non-metal by transferring of one or more electron from the
outermost shell of the metal to the outermost shell of the
nonmetal to complete the outermost shell of each one to the
electronic configuration of the nearest inert gas .
Metal-------Metal
Chemical bonding may also be formed between two metals via
accumulation and rearrangement of these metals in a shape of
metallic crystal.
TYPES OF CHEMICAL BONDS:
The covalent bond: It is formed between atoms of two non-metals similar
or different by sharing electrons.
Single covalent bond: A bond formed by sharing of one pair of electrons
between two non-metallic atoms where each atom shares one electron .
Double covalent bond: A bond formed by sharing of two pairs of electrons
between two non-metallic atoms where each atom shares two electrons.
Triple covalent bond: A bond formed by sharing of three pairs of electrons
between two non-metallic atoms where each atom shares three electrons.
The ionic bond:
It is formed between a metal and non-metal by transferring of one electron
or more from the outermost shell of the metal to the outermost shell of the
non-metal.
The outermost shell of an atom of a metal contains less than 4 electrons (1 ,2
or 3).
 Ions of metals are always positive because the metals tend to lose the
electrons of the outermost shell, so the number of protons is greater than
electrons.
The outermost shell of non-metallic atom contains more than 4 electrons (5,6
or 7).
 Ions of non-metals are always negative because non-metals tend to gain
electrons, so electron number is greater than proton number.
Formation of ionic bond:
An electrostatic force of attraction is developed between the positive ion
and negative ion forming an ionic compound.
Formation of NaCl:
Atom of metal loses electrons and changes into positive ion. Sodium atom
(atomic number = 11):
Atoms of non-metal gains the electrons lost by the metal and changes into
negative ion. Chlorine atom (atomic number = 17):
Note: ionic bonds are strong while covalent bonds are weak.
Polar and non-polar covalent bond (Electronegativity):
Non-polar covalent bond has formed between two identical non-metals such
as H-H,
Br-Br,….. So there is no differences in the electronegativity value
between them. Thus, the covalent bond in this case is considered non-polar
covalent bond.
Polar covalent bond has formed between atoms of two different non-metals
such as H-Cl So the electronegativity between the two atoms is different
where chlorine atom is more electronegative than hydrogen atom.
Therefore, the pair of electrons will attract to the chlorine atom more than
the hydrogen atom. So, chlorine atom will carries partially negative charge
(-δ) while hydrogen atom will carries partially positive charge (+δ),
H+δ – Cl-δ
Thus, the covalent bond in this case is considered polar covalent bond.
In CCl4 : the bond dipoles cancel and the molecule is non-polar.
In CCl3 or in the bent H2O molecule: there is a net dipole, and the molecule is
polar.
Coordinate covalent bond:
The coordinate covalent bond formed between two atoms, the donor atom
and acceptor atom. The donor atom has non-bonding electrons and can
sharing the covalent bond by its non-bonding electrons while the acceptor
atom accepts these non-bonding electrons in its empty orbital.
Coordinate covalent bond examples:
The nitrogen atom in ammonia has one pair of non-bonding electrons and
can make coordinate covalent bond.
The oxygen atom in water has two pair of non-bonding electrons and can
make coordinate covalent bond.
Metallic bond:
Atoms of the same metal are tend to be closed and rearranged in a crystal
shape.
Hydrogen bond:
Hydrogen atom join with an electronegative atom through covalent bond,
where the electronegative atom attracts the pair of sharing electrons and
carries partially negative charge while hydrogen atom carries a partially
positive charge. This bond formed between the molecules of water and
ammonia to increase the cohesion force between molecules.
Van der-Waals force:
These are weak electrostatic forces appears due to the occurrence of a
positive charge and negative charge at the terminals of the molecule causing
attraction between these molecules with others of the same matter.