chemical bonding juniors
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Chemistry for IIT-JEE & other Entrance Exams
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Ionic bonding Covalent bonding
Forms between Forms between
metals and nonmetals
nonmetals and nonmetals
Metallic bonding
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EDUDIGM
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COVALENT BOND is the strong directional electrostatic attraction
between the shared electrons (negatively charged) and the two nuclei
(positively charged) of the bonded atoms.
A covalent bond is formed by the sharing of outermost shell electrons
between two atoms.
A shared pair of electrons (or bond pair) makes a single covalent bond.
So a chlorine molecule Cl2 can be written as ClCl. Cl2 is the molecular
formula of chlorine, while ClCl is the structural formula of chlorine.
O
H
H
Directional
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EDUDIGM
COVALENT BOND
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Double and triple bonds can form between
atoms in order to fill the outer energy level This occurs when two atoms share more than
one pair of electrons
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Some molecules can have more than one
possible Lewis structure, usually when onesingle bond and one double bond can be
exchanged within the rules of drawing Lewis
structures Example of SO2 (g)
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Shapes of some simple molecules as represented by sketches and models.
Ammonia
Methane
Space-filling modelSkeletal atomic modelBall-and-stick modelSketch of shapeMolecule
lonepair
EDUDIGM
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Carbon
dioxide
Ethene
Water
Space-filling modelSkeletal atomic modelBall-and-stick modelSketch of shapeMolecule
H H
O
O = C = O
C = C
H
H
H
H
Shapes of some simple molecules as represented by sketches and models.
EDUDIGM
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IONIC BOND is the strong non-directional electrostatic
force of attraction between oppositely charged ions.
An ionic bond is formed by the transferof one or moreelectrons from one atom (or group of atoms) to another.
IONICBOND
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The reaction of sodium and chlorine .
Sodium Chloride
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Na
loses 1 e-
+
Na
unstable and
reactive
sodium atom (Na) 2, 8, 1 Na ion+
stable
CATION
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Cl
gains 1 e-
_
unstable andreactive
chlorine atom (Cl) 2, 8, 7 Cl ion-
stable
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x
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Cl
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ANION
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When a sodium atom and a chlorine atom react, the sodium atom loses
one electron to the chlorine atom. As a result of this transfer of electron,
two ions are formed.
FORMATION OF IONIC BOND
Sodium Chloride (Salt)
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Ionic Bonds: One Big Greedy Thief Dog!
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Monoatomic ion
(consists of 1 atom
only)
Polyatomic ion
(consists of 2 or more
atoms )
Na+ OH-
K+ NO3-
Ag+ SO42-
Hg+
I-
Cl-
Br-
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1) All simple (single) metal ions are cations.
2a) All simple (single) non-metal ions are anions (except H+).
2b) All polyatomic ions are anions (except NH4+)
3) There is only one common polyatomic cation - NH4+.
4) When a metal forms only one cation, the ion has the same
name as the metal.5) Transition metals are rather unusual- the same metal can form
more than one simple cation with different charges. To name
each ion, a Roman numeral indicating the charge is written in
brackets after the name of the metal.
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7) Simple (single) anion names ending inide
8) Polyatomic anions containing oxygen ofter havenames ending inate orite. The polyatomic anion
with more oxygen is named asate, and that with less
oxygen asite.
9) Ions with 4+ or 4- are uncommon. (unstable)
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Formed between atoms of metallic elements
Electron cloud around atoms
Good conductors at all states, lustrous, very
high melting points
Examples; Na, Fe, Al, Au, Co
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1. Find the sum ofvalence electrons of allatoms in thepolyatomic ion ormolecule. If it is an anion, add one
electron for eachnegative charge.
If it is a cation, subtractone electron for eachpositive charge.
PCl3
5 + 3(7) = 26
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2. The central atom is the
leastelectronegative
element that isnthydrogen. Connect the
outer atoms to it by
single bonds.
Keep track of the electrons:
26 6 = 20
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3. Fill the octets of the
outer atoms.
Keep track of the electrons:
26 6 = 20 18 = 2
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4. Fill the octet of the
central atom.
Keep track of the electrons:
26
6 = 20
18 = 2
2 = 0
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5. If you run out of electronsbefore the central atom hasan octet
form multiple bonds until
it does.
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There are three types of ions or molecules that
do not follow the octet rule: Ions or molecules with an odd number of
electrons.
Ions or molecules with less than an octet.
Ions or molecules with more than eight valence
electrons (an expanded octet).
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If filling the octet of the central atom results in a
negative charge on the central atom and a positive
charge on the more electronegative outer atom,
dont fill the octet of the central atom.
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The only way PCl5 can exist
is if phosphorus has 10
electrons around it.
It is allowed to expand theoctet of atoms on the 3rd
row or below.
Presumably dorbitals in
these atoms participate in
bonding.
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Even though we can draw a Lewis structure for thephosphate ion that has only 8 electrons around thecentral phosphorus, the better structure puts a double
bond between the phosphorus and one of the oxygens.
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This eliminates the charge on the phosphorus and thecharge on one of the oxygens.
The lesson is: When the central atom is on the 3rd
row or below and expanding its octet eliminates someformal charges, do so.