lattice energy

Examples of lattice energy in the following topics:

• Lattice Energy

  • Lattice energy is a measure of the bond strength in an ionic compound.
  • Lattice energy is an estimate of the bond strength in ionic compounds.
  • as the charge of the ions increases, the lattice energy increases
  • as the size of the ions increases, the lattice energy decreases
  • This tutorial covers lattice energy and how to compare the relative lattice energies of different ionic compounds.

• Solutions and Heats of Hydration

  • The greater the value of a compound's lattice energy, the greater the force required to overcome coulombic attraction.
  • In fact, some compounds are strictly insoluble due to their high lattice energies that cannot be overcome to form a solution.
  • The heat (enthalpy) of solution (Hsolution) is the sum of the lattice and hydration energies ( Hsolution = Hhydration + Hlattice energy).
  • A hot solution results when the heat of hydration is much greater than the lattice energy of the solute.
  • Predict whether a given ionic solid will dissolve in water given the lattice energy and heat of hydration

• Ionic Crystals

  • This energy is one definition of lattice energy: the energy released when an ionic solid is formed from gaseous ions binding together.
  • This endothermic reaction gives rise to the other definition of lattice energy: the energy that must be expended to break up an ionic solid into gaseous ions.
  • Lattice energy, while due mainly to coulombic attraction between each ion and its nearest neighbors (six in the case of NaCl) is really the sum of all the interactions within the crystal.
  • Lattice energies cannot be measured directly, but they can be estimated from the energies of other processes.
  • The CsCl lattice therefore assumes a different arrangement.

• Doping: Connectivity of Semiconductors

  • Electrons in free atoms have discrete energy values.
  • In contrast, the energy states available to the free electrons in a metal sample form a continuum of "energy bands."
  • In the atomic lattice of a substance, there is a set of filled atomic energy "bands" with a full complement of electrons, and a set of higher energy unfilled "bands" which have no electrons.
  • The highest energy band contains valence electrons available for chemical reactions.
  • Electrons in the conduction band are free to move about in the lattice and can conduct current.

• The Kinetic Molecular Theory of Matter

  • All particles have energy, but the energy varies depending on the temperature the sample of matter is in.
  • Molecules in the solid phase have the least amount of energy, while gas particles have the greatest amount of energy.
  • The molecules are held closely together in a regular pattern called a lattice.
  • If the ice is heated, the energy of the molecules increases.
  • This is why liquid water is able to flow: the molecules have greater freedom to move than they had in the solid lattice.

• Standard Entropy

  • Scientists conventionally set the energies of formation of elements in their standard states to zero.
  • Entropy, however, measures not energy itself, but its dispersal among the various quantum states available to accept it, and these exist even in pure elements.
  • Graphite, which is built up of loosely-bound stacks of hexagonal sheets, soaks up thermal energy twice as well as diamond.
  • The carbon atoms in diamond are tightly locked in a three-dimensional lattice, preventing them from vibrating around their equilibrium positions.
  • Gases, which serve as efficient vehicles for spreading thermal energy over a large volume of space, have much higher entropies than condensed phases.

• Semiconductors

  • In the classic crystalline semiconductors, electrons can have energies only within certain bands (ranges of energy levels).
  • The energy of these bands is between the energy of the ground state and the free electron energy (the energy required for an electron to escape entirely from the material).
  • In the case of silicon, a trivalent atom is substituted into the crystal lattice.
  • The result is that one electron is missing from one of the four covalent bonds normally part of the silicon lattice.
  • However, once each hole has wandered away into the lattice, one proton in the atom at the hole's location will be "exposed" and no longer cancelled by an electron.

• Crystal Structure: Packing Spheres

  • Consider the arrangement of spheres within a lattice to form a view of the structure and complexity of crystalline materials.
  • Crystalline materials are so highly ordered that a crystal lattice arises from repetitions along all three spatial dimensions of the same pattern.
  • The crystal lattice represents the three-dimensional structure of the crystal's atomic/molecular components.
  • The structure seen within the crystalline lattice of a material can be described in a number of ways.
  • In principle, one can reconstruct the structure of an entire crystal by repeating the unit cell so as to create a three-dimensional lattice.

• Boiling & Melting Points

  • For general purposes it is useful to consider temperature to be a measure of the kinetic energy of all the atoms and molecules in a given system.
  • Thus, in order to break the intermolecular attractions that hold the molecules of a compound in the condensed liquid state, it is necessary to increase their kinetic energy by raising the sample temperature to the characteristic boiling point of the compound.
  • The distance between molecules in a crystal lattice is small and regular, with intermolecular forces serving to constrain the motion of the molecules more severely than in the liquid state.
  • Molecular size is important, but shape is also critical, since individual molecules need to fit together cooperatively for the attractive lattice forces to be large.

• The Third Law of Thermodynamics and Absolute Energy

  • At zero temperature the system must be in a state with the minimum thermal energy.
  • This statement holds true if the perfect crystal has only one state with minimum energy.
  • A more general form of the third law applies to systems such as glasses that may have more than one minimum energy state: the entropy of a system approaches a constant value as the temperature approaches zero.
  • The entropy of a perfect crystal lattice is zero, provided that its ground state is unique (only one), because ln(1) = 0.