Slide 1 : Hydrogen Bond
Hydrogen bond or hydrogen bonding is defined as the electrostatic force of attraction between H-atom (which is already covalently bonded to a highly electronegative atom like N, O or F in a molecule) and a highly electronegative atom present in a molecule of the same substance or present in a molecule of different substance or present within the same molecule. Thus H-bond is formed either between the molecules of the same substance or between the molecules of different substances or between two atoms present in the same molecule. H-bond is represented by a dotted line.
Slide 2 :
Slide 3 :
Slide 4 :
Slide 5 : On the basis of the above discussion we can say that hydrogen bonding is simply dipole-dipole attraction. This dipole-dipole attraction is stronger than other dipole-dipole attractions.
Slide 6 : Conditions for the formation of hydrogen bonds
Presence of highly electronegative atom. The molecule having H-bonds should have a highly electronegative atom like N, O or F directly linked to H-atom by a covalent bond.
Presence of the atom with small size. The highly electronegative atom should be of small size so that B—H bond (B = N, O or F) may be highly polar and a strong interaction between several such dipoles may occur. This explains that, although O and Cl both have almost the same electronegativity (0 = 3.5, Cl = 3.0), O-atom, due to its small size (O= 0.73A, Cl = 0.99A) forms H-bonds while Cl-atom does not do so. On the same lines of argument, it can be explained that O and N can form H-bonds but S and P cannot do so.
Slide 7 : Effect of hydrogen bonding on the physical properties of the compounds containing hydrogen bonds
Slide 8 : Variation in the boiling points of the binary hydrogen compounds of the elements of groups VA, VIA and VIIA. (H = 2.1, N = 3.0, P= 2.1; As = 2.0, Sb = 1.9, 0=3.5, S = 2.5, Se = 2.5, Te = 2.1, F = 4.0, Cl = 3.0, Br = 2.8 and I = 2.5), NH3, H2O and HF molecules undergo inter-molecular hydrogen bonding while the occurence of this type of hydrogen bonding is absent in other molecules. It is because of H-bonding that (NH3)x, (H2O)x, and (HF)x, clusters are formed.
Slide 9 : Comparison between the boiling points of CH4, NH3, H20 and HF.
The boiling points of these hydrides are in the order of :
CH4 (= —161°C) < NH3 ( = —34.5°C) < HF = ( = +19.4°C) < H2O ( = +100°C).
Slide 10 : Viscosity of liquids
Slide 11 : Formation of hydrogen difluoride ion by the combination of F and HF molecule.
Slide 12 : Comparison between the properties of o, m and p-isomers of an aromatic compound.