density

Examples of density in the following topics:

• Volume and Density

  • Density is another measurement derived from SI basic units.
  • Density is calculated by the dividing the mass by the volume, so that density is measured as units of mass/volume, often g/mL.
  • Different substances have different densities, so density is often used as a method to identify a material.
  • An object with a higher density will sink.
  • At that point, the density trend reverses.

• Density Calculations

  • A reformulation of the Ideal Gas Equation involving density allows us to evaluate the behaviors of ideal gases of unknown quantity.
  • Now, recall that density is equal to mass divided by volume:
  • We can substitute in density, D, and get the following:
  • This derivation of the Ideal Gas Equation allows us to characterize the relationship between the pressure, density, and temperature of the gas sample independent of the volume the gas occupies; it also allows us to determine the density of a gas sample given its pressure and temperature, or determine the molar mass of a gas sample given its density.
  • Atmospheric science offers one plausible real-life application of the density form of the ideal gas equation.

• Supercritical Fluids

  • Since density increases with pressure, solubility tends to increase with pressure.
  • At constant density, solubility will increase with temperature.
  • Other properties, such as density, can also be calculated using equations of state.
  • The system consists of 2 phases in equilibrium, a dense liquid and a low density gas.
  • A small increase in pressure causes a large increase in the density of the supercritical phase.

• Recycling and Disposal

  • When placed in a medium of intermediate density, particles of different densities separate-lower density particles float while those of higher density sink.
  • Various separation media have been used, including water or water solutions of known density (alcohol, NaCl, CaCl2 or ZnCl2).
  • As shown in the following table, the densities of common plastics differ sufficiently to permit them to be discriminated in this fashion.
  • Some polymers, such as polystyrene and polyurethane, are commonly formed into foamed solids that have a much lower density than the solid material.

• Properties of Aromatic Compounds

  • Aromatic compounds are ring structures with delocalized $\pi$ electron density that imparts unusual stability.
  • However, the bonding is stronger than expected for a conjugated structure, and it is more accurately depicted as delocalized electron density shared between all the atoms in the ring.
  • Aromatic compounds are cyclic structures in which each ring atom is a participant in a$\pi$ bond, resulting in delocalized $\pi$ electron density on both sides of the ring.

• The Lithium-Ion Battery

  • They are one of the most popular types of rechargeable battery for portable electronics because they have one of the best energy densities and only a slow loss of charge when not in use.
  • Research is yielding a stream of improvements to traditional LIB technology, focusing on energy density, durability, cost, and safety.
  • Handheld electronics mostly use LIBs based on lithium cobalt oxide (LCO), which offer high energy density but have well-known safety concerns, especially when damaged.
  • Lithium iron phosphate (LFP), lithium manganese oxide (LMO), and lithium nickel manganese cobalt oxide (LiNMC) batteries offer lower energy density but longer lives and inherent safety.

• Metallic Crystals

  • Metals in general have high electrical conductivity, high thermal conductivity, and high density.
  • Some metals (the alkali and alkaline earth metals) have low density, low hardness, and low melting points.
  • The majority of metals have higher densities than the majority of nonmetals.
  • Nonetheless, there is wide variation in the densities of metals.
  • The high density of most metals is due to the tightly packed crystal lattice of the metallic structure.

• The Chemical Shift

  • If the electron density about a proton nucleus is relatively high, the induced field due to electron motions will be stronger than if the electron density is relatively low.
  • The shielding effect in such high electron density cases will therefore be larger, and a higher external field (Bo) will be needed for the rf energy to excite the nuclear spin.
  • Since silicon is less electronegative than carbon, the electron density about the methyl hydrogens in tetramethylsilane is expected to be greater than the electron density about the methyl hydrogens in neopentane (2,2-dimethylpropane), and the characteristic resonance signal from the silane derivative does indeed lie at a higher magnetic field.
  • Elements that are more electronegative than carbon should exert an opposite effect (reduce the electron density); and, as the data in the following tables show, methyl groups bonded to such elements display lower field signals (they are deshielded).

• Crystal Field Theory

  • All of the d orbitals have four lobes of electron density, except for the dz2 orbital, which has two opposing lobes and a doughnut of electron density around the middle.
  • On the other hand, the lobes of the dxy, dxz, and dyz all line up in the quadrants, with no electron density on the axes.

• Properties of Sulfur

  • Again, this is accompanied by a lower density but increased viscosity due to the formation of polymers.
  • The density of sulfur is about 2 g/cm3, depending on the allotrope.