Final answer:
The number of molecules in a micelle and its shape are determined by the size, shape of the molecules, and their intermolecular forces. Amphipathic lipids assemble into micelles with hydrophobic cores and hydrophilic surfaces, and factors like tail length and lipid concentration affect micelle formation.
Step-by-step explanation:
The number of molecules in a micelle and its shape depend on the size and shape of its molecules and their intermolecular forces (IMFs). Amphipathic lipids, which have both hydrophilic and hydrophobic properties, self-assemble in water to form micelles. These structures minimize the contact of the lipids' hydrophobic areas with water by sequestering them inside while exposing the hydrophilic heads to the aqueous environment. The spherical arrangement of micelles can be altered by different factors, such as the length and saturation of the lipid tails, the size of the hydrophilic head, and the concentration of the lipids. Molecules with a single hydrophobic tail, like soaps and detergents, often form simple spherical micelles. In contrast, those with two tails, such as phospholipids, tend to form bilayers. The micelle's size and geometry also depend on the temperature and presence of other solutes that can interact with the lipids.
As for viscosity and surface tension, they both are influenced by the size and shape of molecules and their IMFs. Large molecules or those with elongated shapes tend to have more significant surface interaction areas, resulting in stronger IMFs, higher viscosity, and greater surface tension. Conversely, molecules with spherical shapes or smaller sizes tend to have lower viscosity and surface tension. IMFs like London dispersion forces are particularly dependent on molecular shape: molecules with a more significant contact area (like n-pentane) have stronger dispersion forces, whereas those with less contact area (like neopentane) have weaker forces.