CHEMICAL BONDING AND SHAPES OF MOLECULES
Transcript of CHEMICAL BONDING AND SHAPES OF MOLECULES
CHEMICAL BONDING AND SHAPES OF
MOLECULESSANJAYA DWARE
CHEMISTRY DEPARTMENTLITTLE ANGELS’ COLLEGE
Chemical Bonding by SD 12021/09/01
Syllabus– Show structure atoms and ions by Lewis dot method.
– Explain the ionic bond and the properties of ionic compounds.
– Explain the covalent bond, co-ordinate bond and the properties of covalent compound.
– Describe the feature of sigma and Pi-bond
– Describe the co-ordinate covalent compounds with some examples.
– Write the lewis dot diagrams of some ionic and covalent compounds (NaCl, MgCl2, NH4Cl, Oxides of Hydrogen, Nitrogen and Phosphorous, common mineral acids).
– Write the resonance structure of some covalent species.
– Explain the properties of molecular and metallic solids on the basis of vanderwaal’s and metallic bonding.
– Use VSEPR theory to describe the shapes of simple covalent molecules.
– Describe the concept of hybridization in simple covalent molecules.
– Explain the characteristics of bond in terms of dipole moment, Ionic character and bond length.
– Describe the hydrogen bondng and outline the importance of hydrogen bonding to the physical properties of substances, including ice and water (for example, boiling and melting points, viscosity, surface tension and solubility)
Chemical Bonding by SD 22021/09/01
Terminology
■ Valence shells
■ Valence electrons
■ Lewis symbol
Chemical Bonding by SD 32021/09/01
Types of bond
■ Electrovalent bond
■ Covalent bond
■ Coordinate covalent bond
■ Hydrogen bond
■ Metallic bond
■ Van der waal’s bond
Chemical Bonding by SD 42021/09/01
Electrovalent bond or ionic bond
■ The bond formed between two or more than two atoms by the transfer of one or
more electrons among atoms
■ Loss of electrons by an atom of an element forms cation and gain of electrons by an
atom forms anion
■ Cations and anions are held together by an electrostatic force of attraction.
■ The number of electrons lost or gained by an atom of an element is called
electrovalency of the element.
Chemical Bonding by SD 52021/09/01
Chemical Bonding by SD 62021/09/01
Chemical Bonding by SD 72021/09/01
Conditions for the formation of ionic bond
■ Ionisation energy: Energy required to remove the most loosely held electron from an
isolated gaseous atom in its ground state is called ionization energy of that element.
Low ionization energy favors ionic bond.
■ Electron affinity: Energy released when a neutral gaseous atom gains electron
giving an anion is called electron affinity.
High electron affinity favors ionic bond.
■ Lattice energy: Energy released when one mole of the crystal of the compound is
formed from its ions.
Higher lattice energy favors ionic bond.
Chemical Bonding by SD 82021/09/01
Formation of ionic bonds
■ Sodium chloride
■ Magnesium chloride
■ Sodium oxide
Chemical Bonding by SD 92021/09/01
Characteristics of ionic compounds
■ Physical state
■ Solubility
■ Electrical conductivity
■ Brittleness
■ Melting and boiling point
■ Ionic bond is non-directional
Chemical Bonding by SD 102021/09/01
COVALENT BOND
■ Definition: The bond formed by mutual sharing of electrons between combining
atoms of same or different elements
■ Covalency: The number of electrons which its atom contributes for sharing during
the covalent bond formation.
■ Conditions for the formation of covalent bond:
– Electron affinity: elements having nearly equal electron affinity
– Electronegativity: the combining elements having low electronegativity
difference.
– Ionization potential: elements having high ionization potential form covalent
bond.
Electronegativity is defined as a power of an element to attract electrons towards itself in a molecule.
Chemical Bonding by SD 112021/09/01
Formation of covalent bond
■ H2
■ O2
■ Cl2
■ N2
■ NH3
■ HCl
■ CO2 , H2O, CH4 , C2H4 , CH3OH , H2S
HNO3, H2SO4
IONS;
CO3-- , NH4
+ , SO4--, NO3
-
Chemical Bonding by SD 122021/09/01
Properties of covalent compounds
■ Physical state: exist in all three states i.e. solid, liquid and gases.
■ Melting and boiling point: low melting and boiling point.
■ Electrical conductivity: donot conduct electricity as they donot give charged particles
in solution.
■ Solubility: soluble in nonpolar solvents. Eg. Benzene, carbon tetrachloride
■ Directional nature: covalent bonds have directional nature thus have particular
geometrical shape.
Chemical Bonding by SD 132021/09/01
Polarity of a covalent bond:Ionic character of a covalent bond
■ In homonuclear diatomic molecules (H2 , O2 , Cl2 etc. ) the shared electrons are equally distributed between the participating atoms. Such.bonds are called non-polar bonds. Eg. H-H, Cl-Cl, F-F etc.
■ When covalent bond is formed between the atoms of different elements, the atoms of the element having higher electronegativity attracts the shared electrons more towards itself and thus the polarity develops in the bond. Such bonds are called polar covalent bonds. Eg. HCl, HBr, HI etc.
■ Electronegativities in Pauling Scale:
H = 2.1, F = 4.0 , Cl = 3.0, Br = 2.8, I = 2.5
H F H Cl, H Br, H I
Electronegativities diff: 1.9 0.9 0.7 0.4
Polarity of H----X bond decreases
Chemical Bonding by SD 142021/09/01
Dipole moments
■ Definition:
The product of charge (q) on either of the atoms and distant(d) between them is called dipole moment.
It is denoted by µ.
Mathematically,
µ = q x d
where, q = charge on any one atom,
d = distance between the atoms
Dipole moment is a vector quantity.
Unit: Debye (D)
Chemical Bonding by SD 152021/09/01
Applications of dipole moment
■ In the calculation of percentage ionic character
■ In the determination of the polarity of bonds: Greater is the magnitude of dipole
moment of the molecule, higher will be the polarity of the bond.
– If µ = 0, the molecule is non – polar, and
– If µ = 0, the molecule is polar.
■ In the determination of shape of the molecules.
Knowing the dipole moment, the shape of the
molecule can be predicted.
Chemical Bonding by SD 162021/09/01
Chemical Bonding by SD 172021/09/01
Co-ordinate covalent bond or dative bond
■ Definition:
The bond formed by the sharing of electrons between combining atoms, in which both
the shared electrons are contributed by one of the bonded atoms only.
■ The atom which donates the shared pair of electrons is called a donor atom, and the
atom which accepts the shared pair of electrons is called an acceptor atom.
■ Conditions for the formation of a coordinate bond
– The donor atom after the formation of other bonds must be in octet state and
must possess a lone pair of electrons.
– The acceptor atom must require two electrons to attain its nearest noble gas
configuration.
Chemical Bonding by SD 182021/09/01
Formation of coordinate bonds
■ O3 , SO2 , SO3
■ NH4+
■ H3O +
HNO3, H2SO4, H3PO4 , HClO3
IONS;
CO3-- , NH4
+ , SO4--, NO3
-
SALTS
Na2 SO4 , K NO3 , CaCO3
Chemical Bonding by SD 192021/09/01
Formation of coordinate bonds
■ H2SO3,
■ H3PO3 ,
■ SO2Cl2 ,
■ HIO3 ,
■ CH3COONa
Chemical Bonding by SD 202021/09/01
FAILURE OF OCTET RULE
■ Molecules having incomplete octet: BeCl2 , BF3 , AlCl3 , BCl3
■ Molecules having super octet structures : PCl5 , IF7
Chemical Bonding by SD 212021/09/01
HYDROGEN BONDING
■ Definition:
The force of attraction between hydrogen bonded with highly electronegative element (F
or O or N) and highly electronegative element (F or O or N) of same or different molecule
is called hydrogen bond.
Example: water, ammonia, HF, methanol
It is represented by a dotted line.
H----------F- - - - - - - H-------------F - - - - - -H----------Fδ+ δ--
Hydrogen bond
δ--δ--δ+ δ+
Note: Bond energy of hydrogen bond is 2-10kcal/mol whereas bond energy of covalent bond is 50-100kcal/mol.
Chemical Bonding by SD 222021/09/01
TYPES OF HYDROGEN BOND
■ INTERMOLECULAR HYDROGEN BOND:
■ Definition:
■ The force of attraction between hydrogen bonded with highly electronegative
element (F or O or N) and highly electronegative element (F or O or N) of different
molecule is called intermolecular hydrogen bond.
■ Examples: Water, water with methanol, methyl alcohol
Chemical Bonding by SD 232021/09/01
TYPES OF HYDROGEN BOND
■ INTRAMOLECULAR HYDROGEN BOND: The force of attraction between hydrogen
bonded with highly electronegative element (F or O or N) and highly electronegative
element (F or O or N) of same molecule is called intramolecular hydrogen bond.
o-hydroxybenzoic
acid
Chemical Bonding by SD 242021/09/01
O-nitrophenol has lower boiling point than p-nitrophenol. Why?
Intermolecular
Chemical Bonding by SD 252021/09/01
Consequences of hydrogen bonding
■ Water is liquid but H2S is gas at room temperature.
■ Glycerol is more viscous than water.
■ Boiling point of o-nitrophenol is less than that of p-nitrophenol.
■ Decrease in volume during melting of ice.
■ Unusual melting and boiling points of hydrides of group VA, VIA and VIIA
Chemical Bonding by SD 262021/09/01
Unusual melting and boiling points of hydrides of group VA, VIA and VIIA
Consequences of hydrogen bonding
Chemical Bonding by SD 272021/09/01
Van der Waals’ Force
■ Definition:
The short lived attractive force existing between all kind of atoms, molecules and ions,
when they come closer, is called van der Waals’ force.
In 1873, J.D. van der Waals pointed out the force of interaction among the non polar
molecules and atoms.
In 1930, it was explained by Fritz London that the van der waals interaction arises due
to unsymmetrical distribution of electron cloud motion of the electrons around the
nucleus.
Also called as London Forces.
Chemical Bonding by SD 282021/09/01
Metallic Bond
■ Definition:
The simultaneous force of attraction between the mobile electrons and the positively charged core is responsible for holding metal atoms together, which is known as metallic bond.
Electron pool theory■ Metallic lustre
■ Electrical conductivity
■ Malleability and ductility
■ Hardness
■ Thermal conductivity.
Chemical Bonding by SD 292021/09/01
Resonance
■ Definition:
The phenomenon in which a molecule or ion cannot be represented be a
single structure rather it should be represented by more than one
structures to explain its properties, is called resonance.
Examples:
O3
SO3
Benzene
Chemical Bonding by SD 302021/09/01
Chemical Bonding by SD 312021/09/01
Resonating structures of Benzene
Chemical Bonding by SD 322021/09/01
Bonding in solid state
■ Ionic solids
■ Covalent solids
■ Molecular solids
■ Metallic solids
Chemical Bonding by SD 332021/09/01
Thank you
34Chemical Bonding by SD2021/09/01