The document discusses the different types of bonding mechanisms that hold atoms together in solids, including ionic bonding, covalent bonding, metallic bonding, van der Waals bonding, and hydrogen bonding. Ionic bonding involves the transfer of electrons between metals and nonmetals, covalent bonding involves the sharing of electrons between nonmetals, and metallic bonding involves the delocalization of electrons among metal atoms. Weaker van der Waals forces result from induced dipole interactions between molecules. Hydrogen bonding is a special type of dipole-dipole interaction that occurs when hydrogen is bonded to highly electronegative atoms like oxygen or fluorine.

1. Department of Physics, M.E.S Ponnani College
K. Muhammed Abdurahman

2. Energies of Interactions Between Atoms
 Ionic bonding
What kind of forces hold the atoms together in a solid?
 Ionic bonding
 Covalent bonding
 Metallic bonding
 Van der waals bonding
 Hydrogen bonding
15-May-20 2M.E.S Ponnani College

3. Energies of Interactions Between Atoms
• The energy of the crystal is lower than that of the free
atoms by an amount equal to the energy required to
pull the crystal apart into a set of free atoms.
• Binding (cohesive) energy of the crystal.
– NaCl is more stable than a collection of free Na and Cl.– NaCl is more stable than a collection of free Na and Cl.
– Ge crystal is more stable than a collection of free Ge.
Cl Na NaCl
15-May-20 3M.E.S Ponnani College

4. Interactions
Or bonds
Primary
bonds
Secondary
bonds
Van der
Ionic Covalent Metallic
Van der
waals
Hydrogen
All bonding is a consequence of the electrostatic
interaction between the nuclei and electrons.
15-May-20 4M.E.S Ponnani College

5. SI. No: Bond Example Nature of interaction
1. Ionic NaCl Transfer of valence electrons
2. Covalent Diamond Sharing electrons
Types of Bonding Mechanisms
2. Covalent Diamond Sharing electrons
3. Metallic Ag, Cu Free electrons
4.
Van der
Waals
N – solid
Electrons remains associated
with original molecule.
5. Hydrogen Ice -
15-May-20 5M.E.S Ponnani College

6. IONIC BONDINGIONIC BONDING
 Ionic bonding is the electrostatic force of
attraction between positively and negatively
charged ions (between non-metals and metals).
 All ionic compounds are crystalline solids at All ionic compounds are crystalline solids at
room temperature.
 NaCl is a typical example of ionic bonding.
15-May-20 6M.E.S Ponnani College

7. • Metallic elements have valence electrons in their outer shell.
• When losing their electrons they become positive ions.
• Electronegative elements tend to acquire additional electrons to
become negative ions or anions.
Na Cl
15-May-20 7M.E.S Ponnani College

8. • Transfer of electron
• Electro positive and electro negative
• Coulomb attractive force
• After interaction: Similar to inert gas – symmetric
charge distribution
• Cohesive energy – 5 to 10 eV
15-May-20 M.E.S Ponnani College 8

9. • When the Na+ and Cl- ions approach each other closely
enough so that the orbits of the electron in the ions begin to
overlap with each other, then the electron begins to repel
each other by virtue of the repulsive electrostatic coulomb
force.
• To prevent a violation of the exclusion principle, the closer
together the ions, then the potential energy of the system
increases very rapidly resulting a large repulsive force
15-May-20 9M.E.S Ponnani College

10. Na – 1S2 2S2 2P6 3S1
Na+ – 2P6 Ne
Cl – 1S2 2S2 2P6 3S2 3P5 Cl– – 3P6 Ar
• Na+ surrounded by six Cl– and vice versa
• Binding energy = 7.8 eV
• Eg:- KCl, Al2O3, etc
15-May-20 M.E.S Ponnani College 10

11. COVALENT BONDINGCOVALENT BONDING
• Takes place between atoms with small differences in electro
negativity which are close to each other in the periodic table
(between non-metals and non-metals).
• The covalent bonding is formed when the atoms share the
outer shell e– (i.e., s and p e–) rather than by e– transfer.
• Noble gas electron configuration can be attained.• Noble gas electron configuration can be attained.
15-May-20 11M.E.S Ponnani College

12. 15-May-20 M.E.S Ponnani College 12

13. • Each e– in a shared pair is attracted to both nuclei involved in
the bond.
• e– overlap and attraction of nucleus (proton) and e– in a
hydrogen molecule.
e
e
15-May-20 13M.E.S Ponnani College

14. 15-May-20 M.E.S Ponnani College 14

15. • Examples: Cl2 , H2O , O2 , N2 , …….
• Sharing of electron
• Total potential energy, U decreases
• Orbitals overlap effectively
• Orbitals are directionally oriented rather
than spherical symmetric.
• p- orbitals are directional
15-May-20 M.E.S Ponnani College 15

16. Diamond
• Carbon atom, C – 1s2 2s2 2p2
• Modified to – 1s2 2s1 2px
1 2py
1 2pz
1
since 2s & 2p – energy levels are closer
• 4 unpaired electrons – 4 covalent bonds - equal strength• 4 unpaired electrons – 4 covalent bonds - equal strength
• C-C-C bond angle is 109028’
• C – is sp3 hybridized & form tetrahedron
• Each tetrahedron is covalently bonded to 4 tetrahedron
– form a 3D network shape.
15-May-20 M.E.S Ponnani College 16

17. Properties
• Strong bond
• Binding Energy of C = 7.4 eV
• Very hard and brittle• Very hard and brittle
• High Melting and Boiling points
• Poor conductor (but resistivity increases
as temperature increases)
15-May-20 M.E.S Ponnani College 17

18. Comparison of Ionic and Covalent BondingComparison of Ionic and Covalent Bonding
15-May-20 18M.E.S Ponnani College

19. METALLIC BONDINGMETALLIC BONDING
• Metallic bonding is found in metal
elements.
• Partial sharing of valence electrons
• electrostatic force of attraction
between positively charged ions andbetween positively charged ions and
delocalized outer electrons.
• Atoms contribute valence electrons
to a common pool.
• Free electron cloud or gas
+
+
+
+
+
+
+
+
+
15-May-20 19M.E.S Ponnani College

20. 15-May-20 M.E.S Ponnani College 20

21. Sodium - Na
• Na – alkali metal – 1s2 2s2 2p6 3s1
• Two Na atoms come to closes – 3s orbital overlaps
• If 3rd Na atom comes, valence e– occupy 3p state –
(3s & 3p state are closer)
• Na cannot form 2 e– pair with other atoms, since Na• Na cannot form 2 e– pair with other atoms, since Na
have only 1 e–
• Structure of Na – BCC : each Na atom form 1/8th of e–
pair bond with each of its neighbours.
• It is possible only if e– pair resonates among the 8
pair of Na atom.
15-May-20 M.E.S Ponnani College 21

22. Properties of Metallic bonding
• Less directional
• Weaker than ionic and covalent
• Binding energy = 1eV to 5eV
• Low Melting and Boling points• Low Melting and Boling points
• High ductile & malleable
• High thermal and electric conductivity
• High optical reflection and absorption
coefficients.
15-May-20 M.E.S Ponnani College 22

23. VanVan dder Waals Bonder Waals Bondiningg
• Van Der Waals bonds occur between neutral atoms (He, Ne,
Ar, etc) and molecules (O2 , Cl2 , CO2 , CH4 , etc).
• Dipole interaction between atoms
• Temporary dipoles formed in between adjacent atoms due to
natural fluctuations in the electron density of all molecules.
• Temporary dipoles attract one molecule to another - Van der
Waals' force
• Electric field due to dipole induce dipole moment of
neighbour.
• Dipole – induced dipole interaction – Van der Waals bond
• Dispersion bond
15-May-20 23M.E.S Ponnani College

24. • The shape of a molecule influences its ability to form
temporary dipoles.
• Long thin molecules can pack closer to each other than
molecules that are more spherical.
• The bigger the 'surface area' of a molecule, the greater the
van der Waal's forces will be.
Homonuclear molecules,
such as iodine, develop
temporary dipoles due to
natural fluctuations of electron
density within the molecule
Heteronuclear molecules,
such as H-Cl have permanent
dipoles that attract the opposite
pole in other molecules.
15-May-20 24M.E.S Ponnani College

25.  Van der waals interaction occurs generally between
 Dipoles formed as the charge centers of one atom displaced
(do not coincides) in the presence of other.
 Van der waals interaction occurs generally between
atoms which have noble gas configuration.
van der waals
bonding
15-May-20 25M.E.S Ponnani College

26. Properties of Van der Waals bond-
• Binding energy = 0.1 eV/bond
• Non directional
• Liquified at low temperature
• Very weak force (Van der Waal's forces are of the• Very weak force (Van der Waal's forces are of the
order of 1% of the strength of a covalent bond)
• At room temperature, Ethermal > BE - exist in
gaseous state.
• Very low Melting and Boiling point
• Poor conductor of heat and electricity.
15-May-20 M.E.S Ponnani College 26

27. Hydrogen BondıngHydrogen Bondıng
• A hydrogen atom, having one electron, can be covalently bonded to
only one atom. However, the hydrogen atom can involve itself in an
additional electrostatic bond with a second atom of highly
electronegative character such as fluorine or oxygen. This second
bond permits a hydrogen bond between two atoms or strucures.
 Hydrogen bonds connect water
molecules in ordinary ice.
Hydrogen bonding is also very
important in proteins and
nucleic acids and therefore in
life processes.
15-May-20 27M.E.S Ponnani College

28. • Interaction (not usual bond)
• Intermolecular rather than intramolecular
• A sub-covalent bonding
• Dipole – dipole interaction
Hydrogen BondıngHydrogen Bondıng
• Dipole – dipole interaction
• Strength – 1% of covalent bond only - varies
from 0.1 to 0.5 eV/atom
15-May-20 M.E.S Ponnani College 28

29. 15-May-20 29M.E.S Ponnani College

30. 15-May-20 M.E.S Ponnani College 30