Chemical Bonding Juniors

7/31/2019 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

3

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

4

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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

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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.

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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

xx

xx

x

x

x

xx

xx

xx

xx

xx

Cl

xx

xx

x

x

x

xx

xx

xx

xx

xx

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.


26 6 = 20 18 = 2


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4. Fill the octet of the

central atom.


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.

Chemical Bonding Juniors

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