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all about chemical bonding

these slides will help you learn all the basic about chemical bonding. concept of valancy, concept of electronic configuration, types of chemical bonds, and how do atoms form bonds.

1 of 46
Chemical bonding
Valency?
Definition
No. of unpaired electrons in an atom is called valency of that atom
e.g.
Valency= 01
Valency= 01
Assignment:- write valencies of Mg, Ca, Iodine, Xe
Stability of atoms
 Stability= surety of existence.
 Stability is need of everybody; students study to get a secure career.
 Everybody utilize energy to get stability
 Atoms having unpaired electrons are unstable
 Like everything in the universe atoms want to be stable
 Atoms get stable when they have all paired electrons.
unstable
Octate rule:
Atoms are stable when they have 08 electrons in their last shell.
Just count electrons in the last shell.
So, to know atom is stable of unstable; we must write electronic configuration.
But it is very difficult work to do??????
What is the easier solution????
Electrons in last shell= 04
How do atoms complete 08 electrons in the last
shell?
unstable
Need 07 electrons
to become stable
Very difficult..?
There is an
easy way
Loose one electron
in the last shell
unstable
Need 01 electrons
to become stable
Very easy..?
stable
stable
Assignment:-
find
out
what
Br
and
Li
can
do
to
become
stable?
Get 08 electrons by
loosing and gaining
all about chemical bonding
unstable
Need 03 electrons
to become stable
Loose 05 e or
get 03 e?
Need 04 electrons
to become stable
Loose 04 e or
get 04 e?
Get 08 electrons
by mutual sharing
unstable
Lesson learnt! Atoms help each other to become stable.
Atoms help each other by two ways: 1) by sharing electrons 2) by gaining/loosing es
This help of atoms for each other is called chemical bond.

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all about chemical bonding

  • 1. Chemical bonding Valency? Definition No. of unpaired electrons in an atom is called valency of that atom e.g. Valency= 01 Valency= 01 Assignment:- write valencies of Mg, Ca, Iodine, Xe
  • 2. Stability of atoms  Stability= surety of existence.  Stability is need of everybody; students study to get a secure career.  Everybody utilize energy to get stability  Atoms having unpaired electrons are unstable  Like everything in the universe atoms want to be stable  Atoms get stable when they have all paired electrons. unstable
  • 3. Octate rule: Atoms are stable when they have 08 electrons in their last shell. Just count electrons in the last shell. So, to know atom is stable of unstable; we must write electronic configuration. But it is very difficult work to do?????? What is the easier solution???? Electrons in last shell= 04
  • 4. How do atoms complete 08 electrons in the last shell? unstable Need 07 electrons to become stable Very difficult..? There is an easy way Loose one electron in the last shell unstable Need 01 electrons to become stable Very easy..? stable stable Assignment:- find out what Br and Li can do to become stable? Get 08 electrons by loosing and gaining
  • 6. unstable Need 03 electrons to become stable Loose 05 e or get 03 e? Need 04 electrons to become stable Loose 04 e or get 04 e? Get 08 electrons by mutual sharing unstable Lesson learnt! Atoms help each other to become stable. Atoms help each other by two ways: 1) by sharing electrons 2) by gaining/loosing es This help of atoms for each other is called chemical bond.
  • 7. Chemical Bond • Bond =attraction • Attraction between atoms that holds them together • All atoms trying to achieve a stable octet Types of chemical bonds Covalent bond Ionic bond Chemical bond formed by mutual sharing of electrons Chemical bond formed by loosing or gaining electrons
  • 8. Which bond will be formed between two atoms? Covalent or ionic bond? Wants to lose e Wants to gain e Ionic bond will be formed between these two atoms Wants to gain e Wants to gain e covalent bond will be formed between these two atoms
  • 9. Covalent Bond is formed;  When both atoms want to gain electrons, e.g., Cl-Cl, N-N  When both atoms want to share electrons e.g., C-C  When one atom wants to share electron and other atom wants to gain electron e.g., C-Cl, C- O Ionic Bond is formed;  When one of the atoms wants to lose electrons, no matter other atom wants to share or gain electrons e.g., Na-Cl, Na-C etc.
  • 10. Chemical bond formed by mutual sharing of electrons But how does atoms mutually share electrons…???? Answer is given by two theories 01) Valence Bond Theory 02) Molecular Orbital Theory Covalent Bond
  • 11. 01) Valence Bond Theory  It was proposed by Heitler and London in 1927  According to this theory, covalent bond is formed when two half filled atomic orbitals overlap with each other  Electron of each orbital now lives as pair of electron  This pair of electron is shared by both atoms  But atomic orbital of each atom is still separate, so no new orbital is formed Overlapping = the penetration of orbitals in each other is called overlapping of orbitals.
  • 12. Types of orbital overlapping Head-to-head overlapping =sigma bond (a covalent bond formed by Head-to-Head overlap of Orbitals Is called sigma bond) along inter nuclear axis Side ways overlapping =pi bond (a covalent bond formed by Side ways overlap of orbitals Is called pi bond) parallel to internuclear axis Head Head Side way Side way inter nuclear axis inter nuclear axis
  • 13. Head-to-head Overlapping (sigma bond) Overlapping along inter nuclear axis H H 1S orbital 1S orbital S-S orbital overlap H 1S orbital F 2p orbital S-p orbital overlap F 2p orbital F 2p orbital p-p orbital overlap Types of Head-to-head overlap 01 03 02 all overlaps are equally strong…? NO
  • 14. Which overlap is strong overlap..? Charge Distribution S-orbital Uniform Charge Distribution p-orbital Directional Charge Distribution  For a strong bond formation; electron must remain in the region where orbitals are overlapping  Due to uniform charge distribution in s- orbital, electron can not be available in the region where orbitals are overlapping  P-orbital has directional distribution and electrons are found in the head of p-orbital. Therefore, electron will be available in the region where orbitals are overlapping  Therefore;  p-p>s-p>s-s
  • 15. Side ways overlapping =pi (π) bond Weak bond
  • 16. Valence Shell electron pair repulsion theory  This theory was proposed by; Sigwick and Powell in 1940  There are two types of electron pairs in the valence shell of central atom I) lone pairs II) Bond pairs  Being –vely charged, electron pairs repel each other  Strength of repulsion is lone pair-lone pair>lone-pair-bond pair>bond pair-bond pair repulsion  Due to this repulsion, electron pairs in the central atom arrange themselves in such a way that they experience minimum repulsion  The pattern of arrangement gives geometrical shape to molecule
  • 17. Shapes of molecules according to VSPERT
  • 18. What is the Shape of Ammonia (NH3) molecule according to VSPERT..? Steps: 1. write the molecular formula 2. write the central atom 3. Write the surrounding atom 4. Structure of molecule 5. Count total e- pairs in valence shell of central atom 6. Count bonding e- pairs in valence shell of central atom 7. Count lone e- pairs in valence shell of central atom NH3 N H 04 03 01
  • 19. Hybridization  This concept was given by Linus Pauling  During bond formation Atomic orbitals of central atom mix with each other to make a new type of orbital called a hybrid molecular orbital.  Only those atomic orbitals mix which have electrons  The number of hybrid orbitals formed is the same as the number of atomic orbitals that were mixed.  The type of hybrid orbital formed depends on the types of atomic orbitals mixed.  Hybridized orbitals are lower in energy compared to nonhybridized orbitals. CH4 01 S orbital + 03 p orbitals=04 sp3
  • 20. Water-H2O Central Atom (O) 01 S orbital + 03 p orbitals=04 sp3
  • 21. Ammonia- NH3 Central Atom (N) 01 S orbital + 03 p orbitals=04 sp3
  • 22. Boron trifrlouride- BF3 Central Atom (B) 01 S orbital + 02 p orbitals=03 sp2
  • 23. Beryllium Chlouride-BeCl2 Central Atom (Be) 01 S orbital + 01 p orbitals=02 sp
  • 24. Types of hybridization Sp3 Sp2 Sp Mixing orbitals Hybridization Shape of molecule Bond angle 01 S + 03 p Sp3 tetrahedral 109.5° 01 S + 02 p Sp2 trigonal 120° 01 S + 01 p Sp linear 180°
  • 25. Limitations of Valence Bond Theory 1) It gives No information about bond order of a molecule 2) It Can not explains magnetic properties of a molecule 3) It can not explain 04 valency of Carbon, 03 Valency of boron, and 02 valency of Beryllium
  • 26. Molecular Orbital Theory  It was proposed by Mullikan, Hund and Huckle in 1927  According to this theory, covalent bond is formed when two half filled atomic orbitals of similar energy combine with each other and generate new orbitals called as molecular orbitals  In atomic orbital electron is influenced of parent nucleus; while in molecular orbital, electron is influenced by both nuclei.  The number of molecular orbitals formed is the same as the number of atomic orbitals that were combined.  Two types of MO are formed; one having higher energy, and other having lower energy  higher energy MO is called Anti bonding molecular orbital  Lower energy MO is called bonding molecular orbital  Electrons are filled in molecular orbitals as per basic electronic configuration rules; Afbau, hund rule etc.
  • 27. Advantages of Molecular Orbital Theory 1) It gives information about bond order of a molecule 2) It explains magnetic properties of a molecule bond order of a molecule= how many bonds will be formed. If the molecule has any unpaired electron, it will be paramagnetic (attracted to external magnetic field) If no unpaired electron, it will be diamagnetic (repelled by external magnetic field)
  • 28. Valence Bond Theory Molecular Orbital Theory Only unpaired electrons of valence shell are involved in bonding All electrons of valence shell are involved in bonding Atomic orbitals do not loose their identity Atomic orbitals convert into molecular orbitals VBT does not talk about bond order MOT helps determine bond order of the molecule Magnetic properties of molecules can not be explained MOT explains the magnetic properties Valence Bond Theory Vs Molecular Orbital Theory
  • 29. Hydrogen Molecule-H2 02 00 = 01 Anti-Bonding orbital Bonding orbital There is no unpaired electrons in the molecule; therefore, it is diamagnetic
  • 30. Oxygen Molecule-O2 08 04 = 02 There are two unpaired electrons in the molecule; therefore, it is paramagnetic
  • 31. Ionic Character in covalent bond Covalent bond= mutual sharing of electrons. Mutual sharing between two same atoms Homoatomic molecule Mutual sharing between two different atoms Heteroatomic molecule Is electron pair equally shared between two atoms..? Each atom of molecule try to attract shared pair of electron. The stronger atom is successful in keeping shared pair of electron slightly towards itself. In homoatomic molecules both atoms are of same strength. Therefore; e- pair is equally shared. In heteroatomic molecule both atoms have different strength, therefore; e- pair is slightly towards stronger atom Atom to which e- pair is slightly closer gets slightly –ve charge on it While the other atom becomes slightly +ve. (Polar Molecule) (Non-Polar Molecule)
  • 32. Dipole Moment Di=two pole=charges Molecule which has ionic character is called a dipole/polar molecule Dipole Moment µ It is measurement of polarity of molecule Dipole Moment Formula ... A dipole moment is the product of the magnitude of the charge (q) and the distance between the centers of the positive and negative charges (d) µ=q.d SI unit= coulomb.meter Common unit=debye 1 debye =3.335× 10-30 C m For Nonpolar molecules µ=0 For polar molecules µ>0
  • 33. Bond Energy Amount of energy required to break the bonds of 1 mole of substance is called Bond Energy Factors Affecting bond energy B.E ∝ Ionic character in covalent bond B.E 1/∝ Bond Length Bond Length=distance between centers of covalently bonded atoms 1.2 Ao 1.34 Ao
  • 35. States of Matter H2O H2O H2O H2O
  • 36. Difference in arrangement of molecules Tightly packed Each molecule is free to move Molecules are far apart Can not move Molecules are close together but can move freely How molecules stay together? Solid Liquid Gas States of matter
  • 37. Why there are different states of matter?? Van der walls force weak electric forces that attract molecules to one another.
  • 39. How to decide which will be the normal state of a given substance….? Normal temperature=room temperature= 25 C Normal pressure= 1 atm State of matter depend on distance between molecules. State of matter depend on temperature and pressure. Boiling Point:-the temperature at which the material transforms into the gas phase Melting point:-The temperature at which solid changes its state to liquid at atmospheric pressure
  • 40. States of Matter- GASES A gas is one of the four fundamental states of matter consisting of particles that have neither a defined volume nor shape.
  • 41. Collisions of Gas Particles
  • 42. Collisions of Gas Particles
  • 44. Kinetic Molecular Theory Postulates of the Kinetic Molecular Theory of Gases 1. Gases consist of tiny particles (atoms or molecules) 2. These particles are so small, compared with the distances between them, that the volume (size) of the individual particles can be assumed to be negligible (zero). 3. The particles are in constant random motion, colliding with the walls of the container. These collisions with the walls cause the pressure exerted by the gas. 4. The particles are assumed not to attract or to repel each other. 5. The average kinetic energy of the gas particles is directly proportional to the Kelvin temperature of the gas
  • 45. Kinetic Molecular Theory (KMT) 1. …are so small that they are assumed to have zero volume 2. …are in constant, straight-line motion 3. …experience elastic collisions in which no energy is lost 4. …have no attractive or repulsive forces toward each other 5. …have an average kinetic energy (KE)that is proportional to theabsolute temp. of gas (i.e., Kelvin temp.) AS TEMP. , KE  explains why gases behave as they do  deals w/“ideal” gas particles…