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A covalent bond is formed when two or more
nuclei share electrons in order to achieve a
stable electron configuration (noble gas).
Covalent bonds often occur between two nonmetals of the same element. (Diatomics)
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H,O,F,Br,I,N,Cl
Atoms of different elements can also combine
to form a covalent bond.
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Example: water, carbon dioxide
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There are different types of covalent bonds.
They are:
Non-polar Covalent
 Polar Covalent
 Multiple Covalent
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 Double bonds
 Triple bonds
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A nonpolar covalent bond exists when there is
an equal sharing of electrons between two
nuclei.
Nonpolar covalent bonds are formed between
atoms having equal or close electronegativity
values.
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The diatomics always make nonpolar covalent bonds
because they are non-metals and their
electronegativity values cancel.
If the electronegativity different is between 0 and 0.4
the compound is considered nonpolar covalent.
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Atoms involved in a polar covalent bond have
an unequal sharing of electrons.
This can be determined based on their
differences in electronegativity.
The element with the higher electronegativity
value attracts the shared electrons more
strongly.
This causes a portion of the molecule to acquire
a partially negative charge.
The other end of the polar molecule acquires a
partially positive charge.
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H-Cl and H-I are two common polar
compounds.
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Hydrogen obtains a partially positive charge and the
halogens obtain a more negative charge.
This happens because the halogens (group 17) have a
higher electronegativity value than hydrogen.
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Water is a polar covalent compound.
In a water molecule, the oxygen atom takes on
the negative charge and the hydrogens take on
the positive charge.
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Atoms in covalent bond may share more than
one pair of electrons.
This additional sharing of electrons results in
the formation of a multiple covalent bond.
Double bond- the sharing of two pairs of
valence electrons.
Triple bond- the sharing of three pairs of
valence electrons.
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Every Hydrogen atom has one line connecting
it to other atoms or itself. (single bond)
Every Oxygen atom has two lines connecting it
to other atoms or itself. (double bond)
Every Nitrogen atom has three lines connecting
it to other atoms or itself. (triple bond)
Every Carbon atom has four lines connecting it
to other atoms. (not itself because Carbon is not
diatomic) – (single bonds)
H
H
(single)
O
O
(double)
N
N
(triple)
Cl
Cl
(single)
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A molecule is the smallest discrete particle of an
element or compound formed by a covalent bond.
Each atom in a molecule obtains an electron
configuration of a noble gas.
Molecular substance can either be solid, liquid, or
a gas.
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The state of matter depends on the strength of the forces
of attraction.
Molecules tend to be soft, poor conductors of heat
and electricity, and they have low melting and
boiling points.
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A large majority of all chemical compounds on
Earth are covalent (either polar or non-polar).
A vast majority of covalent compounds are
organic, meaning they contain carbon and
hydrogen.
Plastics, foods, living things, oil, etc. are all
organic compounds.
There are thousand of these compounds and
we use them everyday.
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If a molecule contains polar bonds does not
mean that the compound itself is polar.
For example, the Hydrogen – Carbon bond is
polar but the compound CH4 is a non-polar
compound.
To understand this, one must look at the
molecules shape.
Asymmetrical molecules are polar
Symmetrical molecules are non-polar because
the pull of the various polar bonds offset each
other .
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Polyatomic ions are two or more different
atoms bonded together that act as one unit.
Polyatomic ions must also contain an ionic
bond to be considered stable.
The bonds that hold the polyatomic ion
together are covalent.
A polyatomic ion plus a metal will contain both
ionic and covalent bonds.
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Ionic, metallic, and covalent bonds all have
different properties.
This table explains the main difference between
all three
Bond
Melting/Boiling
Hardness
Conductivity
S
L
Aq.
Metallic
High
Hard
Yes
Yes
Yes
Covalent
Low
Soft
No
No
No
Ionic
High
Hard
No
Yes
Yes
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Molecules have attractive forces acting on them
in the solid, liquid and gaseous state.
These forces are:
Ionic forces
 Dipole forces
 Hydrogen bonding
 Induced dipole
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