Question

Hydrogen bonds and hydrophilic interactions are
A) Strong chemical bonds that hold together the atoms within a molecule B) Weak chemical bonds that hold together the atoms within a molecule C) Strong chemical bonds that link together separate molecules D) Weak chemical bonds that link together separate molecules

Answer 1

Answer:

Hydrogen Bonding

A hydrogen bond is the interaction of a hydrogen atom with an electronegative atom, such as nitrogen, oxygen, or fluorine from another molecule. The hydrogen must form covalent bond with another electronegative atom to create the bond. These bonds can occur between molecules or within different parts of a single molecule [19]. The hydrogen bond that was generally from 5 to 30 kJ /mol is stronger than a van der Waals interaction, but weaker than covalent or ionic bonds.

A hydrogen attached to carbon can also participate in hydrogen bonding when the carbon atom is bound to electronegative atoms, as is the case in chloroform, CHCl3. The electronegative atom attracts the electron cloud, from around the hydrogen nucleus and, by decentralizing the cloud, leaves the atom with a positive partial charge. Because of the small size of hydrogen relative to other atoms and molecules, the resulting charge, though only partial, nevertheless, represents a large charge density. A hydrogen bond results, when this strong positive charge density attracts a lone pair of electrons on another heteroatom, which becomes the hydrogen-bond acceptor.

Usually, the partially covalent nature of a hydrogen bond is simple to determine on the basis of inter-atomic distances in the X-H-Y system. X-H distance is typically about 110 pm, whereas H-Y distance is from 160 to 200 pm. Hydrogen bonds can vary in strength from very weak (1–2 kJ/mol) to extremely strong (over 155 kJ/mol) [20]. The length of hydrogen bonds depends on bond strength, temperature, and pressure. The bond strength itself is dependent on temperature, pressure, bond angle, and environment.

Many materials are strengthened by hydrogen bonds in their main chains. The best known example is nylon, where hydrogen bonds occur in the repeat unit, and plays a major role in the crystallization of the material. The bonds occur between carbonyl and amine groups in the amide repeat unit. They effectively link the adjacent chains to create crystals, which help reinforce the materials. The effect is greatest in the structure of aramid fiber, where hydrogen bonds stabilize the linear chains laterally, as shown in Fig. 4-2. The chain axes are aligned along the fiber axis, making the fibers extremely stiff and strong. The hydrogen bond networks make both the natural and sensitive materials to humidity levels in the atmosphere because water molecules can diffuse into the surface and disrupt the network. Some materials are more sensitive than others.

Answer 2

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D). weak chemical bonds that link together separate molecules.