Because electrons are in constant motion, the center of a negative charge in a molecule is also in constant motion. There are no permanent dipole-dipole interactions in nonpolar compounds, yet lipids exhibit a variety of intramolecular forces nonetheless. In contrast to polar molecules like water and vinegar, the oils we use in our lotions or vinaigrettes belong to a class of molecules called lipids, which are defined by their solubility in nonpolar organic solvents. Because the sodium and chloride atoms in salt are joined by an ionic bond, NaCl will dissociate into Na + and Cl – in water, allowing for the dipoles of the water molecule to create hydrogen bonds with the salt atoms. A great example of this is when we try to dissolve salt (NaCl) in water. When dipole-dipole interactions are extremely strong, such as in the case of water, this is called hydrogen bonding. From a thermodynamics standpoint, these dipole-dipole interactions are energetically favorable, and allow the solute to “dissolve” in the solvent. When polar molecules are placed into a polar solvent (such as salt into water), the molecules will orient themselves such that the partial positive charge of one molecule can efficiently interact with the partial negative charge of an adjacent molecule. While covalent bonds do not exhibit a net charge, there can be an unequal sharing of electrons leading to an electric dipole across a bond.įor polar compounds like water, the presence of an electric dipole (partial charge on either end of the molecule) opens up opportunities for dipole-dipole interactions with other molecules. This means that oxygen, with its stronger electronegativity, will exert a stronger pull on the electrons shared between hydrogen and oxygen in the covalent bond, leading to a partial positive charge at the hydrogens, and a partial negative charge at the oxygen. The electronegativity of oxygen is 3.44, whereas the electronegativity of hydrogen is 2.20. Water is made up of 2 atoms, oxygen and hydrogen, that share electrons through a covalent bond. Atoms with higher electronegativities (such as oxygen or fluorine) will exert a stronger “pull” on electrons shared in a covalent bond.įor example, let’s look at water. As it is understood, polarity is dependent on the electronegativity of each atom in a molecule. The concept of solubility involves examining how a solute interacts with a solvent, which is primarily dictated by the polarity of both the solute and the solvent. Solubility, Intermolecular Forces and, Thermodynamics
Emulsion chemicals skin#
You can even bring this back to our biology to understand the interplay of lotions and our skin cells. Hence, light scattering and other “physics” concepts can be explored through lotions. Additionally, the molecules in an emulsion organize at scales similar to the wavelengths of light, which lead to an opaque appearance. We can bring the science of lotions back to the classroom in so many ways! For one, they are a great way to talk about intermolecular forces. As it turns out, lotions are a complex mixture of different substances that need to be combined - in certain proportions - in order to stably interact. We know lotions as creamy products that feel great on our skin. We encounter these types of mixtures everyday - in cosmetics, food, medicine, and some household products. To a chemist, however, lotions represent a mixture where normally immiscible (unmixable) liquids are combined in a way that evenly distributes one of the immiscible liquids into the other, without dissolving it. In terms of marketing and advertising, lotions are typically lumped into the “cosmetics” category. This is true for the water and oil components that we are working to combine in a lotion. This is because vinegar and oil are chemically incompatible. In the case of lotions, we can employ a tool such as a stick blender.Īnyone who has combined oil and water knows that, regardless of how much you mix and shake, the vinaigrette will quickly separate into the oil phase (top) and water phase (bottom). To effectively combine water-based vinegar with oil, we might use a whisk or blender. Another example of this type of mixture lies in the kitchen when making a vinaigrette. This typically requires a rigorous mechanical force to shear and disperse one liquid into the other.
In creating lotion emulsions, we are combining oil-based liquids and water-based liquids such that the end product appears as a uniform substance. An emulsion is a specific type of colloid because all the components of an emulsion are liquids. Emulsions are a specific type of colloid, or a mixture where microscopic particles are dispersed - without being dissolved - throughout another substance.
0 kommentar(er)
