كيمياء لغات الباب الثالث شرح بالفيديو 3ث CHEMICAL COMBINATION

CHEMICAL COMBINATION


Introduction: for an element to be stable, its outermost energy
level should be completely filled, so that all elements (except noble
gases) undergo chemical reactions to acquire an identical electronic
configuration. as that of the nearest noble gas, that’s by losing ,
gaining or sharing, through forming chemical bonds.

*If a chemical bond is not formed or broken amongst the atoms , there is no

chemical reaction

For example :- *If Iron fillings mixed with sulphur powder , the product

is not a chemical compound but it is a mixture

*If this mixture is heated to high enough temp. it forms new

compound and this is called chemical reaction

Chemical reaction:-

Def :- Breaking bonds between atoms in reactants and forming new bonds

between atoms in products

These bonds are: - 1) Ionic bond 2) Covalent bond 3) Coordinate bond

4) Hydrogen bond 5) Metallic


1) IONIC BOND


Def : - * It’s a bond formed by transfer one or more electrons

from metal to non-metal

* Electrostatic attraction force takes place
between cation and anion. So ionic bond has no materialistic existence.

Steps 1) Metal loses one or more electrons to form positive ion[ cation]

2) Non-metal gains that electron to form negative ion (anion)

3) Cations and anions are attracted to each other forming ionic

compound.



EX.

Na 1S2 , 2S2, 2P6 , 3S1 17Cl 1S2 , 2S2, 2P6 , 3S2,3P5



Na+1 1S2 , 2S2 ,2P6 Cl-1 1S2 , 2S2 , 2P6 , 3S2 , 3P6

Attraction force

Na+1 ــــــــــــ Cl-1

G.R.F

1- Ionic bond is formed between the two extremes of the periodic table.

2-Elements of group 1A form Ionic bond with elements of group 7A


*Because elements at the left hand side of the periodic table

characterized by a large volume and a small ionization energy so electrons

easily loosed from the outer level forming cation.

but elements at the right hand side of the periodic table characterized by

small volume and high electron affinity so electrons easily gained [anion].

* Effect of electronegatirity on the strength of the ionic bond

* There is a relation between the difference in electronegativity
between atoms in ionic compound and the strength of ionic bond.

* When the difference in electronegativity increases the strength of ionic bond increases. as shown in the table

* Ionic compounds are formed if the difference in electronegativity between the two bonded atoms is more than (1.7).

Group I II III

Element Sodium Magnesium Aluminium

Electro negativity 0.9 1.2 1.5

Chloride compound NaCl MgCl2 AlCl3

Diff in E.n 3- 0.9 = 2.1 3 –1.2 = 1.8 3 – 1.5 = 1.5

M.p 810C0 714 C0 190 C0

B.p 1465 C0 1412 C0 Sublimes'

Conductivity Very good conductor Good conductor Does not conduct





2) COVALENT BOND



Def :- It’s a bond formed between two non-metals by sharing
electrons in order to reach the stable electronic configuration as the
nearest noble gas.

* Types of covalent bonds


Pure covalent bond Polar covalent bond

It is formed between two similar atoms have the same electronegativity

EX H2 , O2 , N2 It is formed between two different atoms have the difference in electronegativity

HCl , NH3 , H2O

Diff. in electronegativity between atoms equals zero Diff in electronegativity between atoms is less than 1.7

Every atom in the molecule has the same ability to attract
electrons of the chemical bond The atom of more electronegativity has
greater ability to attract electrons of the chemical bond

The electron pair spends the same time in the vicinity of each
atom The electron pair spends more time in the vicinity of each atom


*When difference in electronegativity equals zero bond will be pure covalent

*When difference in electronegativity is less than 1.7 bond will be Polar covalent

*When difference in electronegativity more than 1.7 bond will be ionic




G.R.F

1- The bond formed between two Fluorine ,Chlorine or Hydrogen atoms in

a diatomic molecule is a pure covalent bond.

*Because each atom in the molecule has the same ability to
attract the two shared electrons of bond so the electron pair spends the
same time in the vicinity of each atom and the net charge = zero.


4- The bond formed between Hydrogen and Chlorine atoms in Hydrogen

Chloride molecule is a polar covalent bond.

*Because Chlorine has a higher electronegativity than Hydrogen so
it carries a partial negative charge and Hydrogen carries a partial
positive charge due to unequal sharing of the electrons pair .

* Comparison between ionic bond and covalent bond

Ionic-bond Covalent-bond

1 Formed between metal and non-metal Formed between non-metals only

2 one or more electrons transfer from metal to non-metal No
transferring electrons but sharing takes place between two non-metals.

3 Ions are formed ions are not formed

4 Electrostatic attraction takes place between cations and anions. Sharing of electrons takes place between the bonded atoms.

5 Has no materialistic existence (just attraction) G.R.F Has a materialistic existence by the shared electrons.

6 Difference in electronegativity is more than 1.7 Difference in electronegativity is less than 1.7

7 Strong bond G.R.F Weak bond


THEORIES OF COVALENT BONDING

1) Octet-rule “Electronic Theory of Valence” E.T.V

“With the exception of Hydrogen , Lithium and Beryllium ,atoms of all elements tend to reach the octet structure ”

By scientists named (Kossel and Lewis 1916 )

EX

H2 1S1 H H EX H2O 8O 1S2 , 2S2 , 2P4

H O H

EX 17Cl 1S2,2S2,2P6,3S2,3P5

Cl Cl EX NH3 7N 1S2,2S2,2P3

H N H

H


* Inadequacies of octet rule :- [Exam 2007]

1) It can’t explain the bonding in some molecules such as

boron trifluoride BF3 and phosphorus pentachloride. PCl5

2) It is not sufficient to explain many of covalent properties

such as the stereo structure and angle between bonds

G.R.F Boron triflouride and phosphorus penta chloride disobey octet rule.










Which of the following compounds obey or disobey the octet rule

Sulphur trifluoride SF3






Sulphur hexafluoride SF6


Sulphur dioxide SO2






Phosphorus pentaoxide P2O5






Phosphorus trichloride PCl3






Carbon dioxide CO2








2) Valence Bond Theory V.B.T


*This theory was based on the conclusions of quantum
mechanics that consider electron not only as negative particle that
moves in a definite orbit , but as a material with wave property which
can exist in any position in the space around the nucleus

Def.:- It explains the formation of the covalent bond as a result
of overlap of an atomic orbital of one atom contains single electron
with orbital of another atom contains single electron.



* HYBRIDIZATION

*It’s the mixing of orbitals of the same atom closed in energy
forming number of equivalent hybridized orbitals which take part in a
chemical bonding.

* Types of Hybridization

Point of comp. Methane CH4 Ethylene C2 H4 Acetylene C2 H2

Type of hyb. Sp3 Sp2 Sp

Number of hyb. orbitals S + 3(P) = 4SP3 S + 2(P) = 3SP2 S + P = 2SP

Shape tetrahedral pyramid

[tetrahedron] planner triangle linear planner

Angle between the hybridized orb. 109o.28 120o 180o

Structure

H

H C H

H H H

C C

H H H ــ C C ــ H

Bonds between 2C - have one pi and one sigma in c-c two pi bonds and one sigma bond

number of bonds four sigma bonds five sigma bonds and one pi bond three sigma bonds and two pi bonds


Note:-

*The hybridized molecular orbitals must protrude to the outside

to be more capable of overlapping than the pure atomic orbital.


HYBERIDIZATION OF METHANE CH4



Ground state 2P2

2S2

6C 1S2


Excited state 2P3

2S1

1S2


Hyb. state

1S2










HYBERIDIZATION OF ETHYLENE C2 H4


2P2 2P2

2S2 2S2

6C 1S2 1S2 6C



2P3 2P3

2S1 2S1

6C 1S2 1S2


pz Pz



1S2 1S2











H H

C C

H H




HYBERIDIZATION OF ACETYLLENE


2P2 2P2

2S2 2S2

6C 1S2 1S2 6C



2P3 2P3

2S1 2S1

6C 1S2 1S2 6C






1S2



Shape:-

Linear planner

Angle:-

180o

Type:- SP

EX. Acetylene or Ethyne


*Conditions of hyberidization

1-Hybridization takes place between orbitals of the same atom.

2-Hybridization takes place between orbitals which closed in energy.

3-Number of hybridized orbitals equals orbitals which share in

hybridization and takes its symbols.

G.R.F

1- Angle between hybridized orbitals in Methane equals to 109.28

2- Angle between hybridized orbitals in Ethylene equals to 1200

3- Angle between hybridized orbitals in Acetylene equals to 1800

* Because the orbitals must go a part as far as possible from the

other orbitals to decreases the repulsion force between orbitals and

at this angle the molecule will be more stable. [ 2006 ]

SP3 hyb. :- it is the common hybridization takes place on mixing one

S orbital and 3p orbitals


3) MOLECULAR ORBITAL THEORY

M.O.T

Def:- All the atomic orbitals of the combined atoms are mixed to
form molecular orbitals. which have the symbols (sigma , pi
, delta )


V.B.T M.O.T

The molecule is formed of two atoms or more. The molecule is a one unit as a big atom with multi nuclei.

Hybridization occurs between some atomic orbitals. Hybridization occurs between all atomic orbitals.


* Compare between ( sigma ) and ( pi ) bonds.

Sigma bond Pi bond

1 Usually formed due to overlap of hybridized orbitals (head to
head) Usually formed due to overlap of hybridized orbitals (side by
side)

2 Strong bond G.R.F Weak bond

3 Due to greater orbital overlap Due to less orbital overlap

4 The overlapped orbital are on

one line (collinear-overlap)

along one axis Overlap between two parallel orbitals (collateral overlap)




3) COORDINATION BOND


Def :- It’s a special type of covalent bond in which the two
electrons required for the bond are donated by one of the two atoms. to
the other atom.

Or It’s a special type of covalent bond formed between two atoms one of them is donor and other is acceptor.

Or It’s a special type of covalent bond formed between two atoms
one of them has lone pair of electron and other has empty orbital.

The atom, which gives that pair of electrons is called donor atom.

The atom, which gains that pair of electrons is called acceptor atom.


EX. (1) – Hydroxonium[Hydronium] ion [ H3O]+1



H O +H+ [ H O H+]

H H 8O 1S2 , 2S2 , 2P4

h4


* Oxygen is a donor atom

* Hydrogen ion is an acceptor


EX. (2) Ammonium ion [ NH4]+



H H

H N +H+ [ H N H+

H H 7N 1S2 , 2S2 , 2P3



* Nitrogen is a donor atom

* Hydrogen ion is an acceptor atom



Compare between Covalent bond and Coordination bond



Covalent bond Coordination bond

DEFINITION





SOURCE OF ELECTRONS OF CHEMICAL BOND


Types of chemical bonds in ammonium ion

1- Polar covalent bond 2-Coordination bond


Types of chemical bonds in ammonia solution

1- Polar covalent bond between Nitrogen and Hydrogen atom

2- Coordination bond between Nitrogen atom and Hydrogen ion .

3- Ionic bond between positive ion and negative ion.


4) THE HYDROGEN BOND

Def :- It’s a bond formed between hydrogen in a polar molecule
and atom in other molecule has a high electronegativity such as Nitrogen
, Oxygen and Fluorine.

*So Hydrogen is a bridge between two bonds one of them is

a polar covalent and other is hydrogen bond

Shapes of hydrogen bond

( linear – closed – open net shaped )


EX : [ water , liquid hydrogen fluoride , ammonia. ]


1) H2O Hـــ O…… Hــــ O ……… Hـــــ O……… HـــO

H H H H

F

2) HF F F F F F H H

H H H H H F F

H Closed ring

H H H

3) NH3 H N H N H N

H H H



G.R.F H2O (18) M.w H2S (34) M.w

Boiling point of water is higher than boiling point of H2S
(hydrogen sulphids) OR [Anomalous of boiling point of water]. G.R.F


*Oxygen atom has a small atomic radius and high electronegativity[3.5] than

hydrogen [2.1] So water is a polar molecule So hydrogen bonds between

water molecules are formed which need amount of energy for broken


*Compare between covalent bond and hydrogen bond .



Point of comparison Covalent bond Hydrogen bond

Length 1A0 [ Shorter ] 3A0 [ Longer ]

Energy 418 Kj [ stronger ] 21 Kj [ weaker ]

Def.





5) METALLIC BOND

*The positive ions of the metal are hold together by the moving electron cloud.

Def :- It’s produced from the electron clouds of valence
electrons which decreases the repulsion forces between the positive
metal ions in the crystal lattice.


11Na 1S2 , 2S2 , 2P6 , 3S1

* It contains (1) electron in delay level

12Mg 1S2 , 2S2 , 2P6 , 3S2

* It contains (2) electrons in delay level

13Al 1S2 , 2S2 , 2P6 , 3S2 , 3P1

* It contains (3) electrons in delay level


G.R.F * Aluminum is hard metal * Manganese is mild * Sodium is soft

If No. of valance electrons increases “strength of metallic bond
increases” and melting point increases. [Sodium has one electron in the
outer level but Magnesium has two electrons but Aluminum has three
electrons]


G.R.F M.P of Al greater than Magnesium greater than Sodium

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