CH 102 1st Edition Lecture 4Outline of Current Lecture I. The Triple PointII. Crystalline Solids and Their StructureIII. Diffraction from a CrystalIV. Crystal LatticeV. Unit CellsVI. Cubic Unit CellsCurrent LectureI. The Triple Pointa. A point on the phase diagram where all three phases, solid, liquid and gas coexistin thermodynamic equilibriumb. Substance c. T (K) d. P (atm)e. Ammonia f. 195.40 g. 0.05997h. Carbon dioxidei. 216.55 j. 5.10k. Hydrogen l. 13.84 m. 0.0695n. Iodine o. 386.55 p. 0.1191q. Nitrogen r. 63.18 s. 0.124t. Oxygen u. 54.36 v. 0.00150w. Water x. 273.16 y. 0.006037II. Crystalline Solids and Their Structurea. Crystalline solids are orderly geometric structures whose lattice points are occupied by atoms, ions, or molecules.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.b. Understanding of solid structure is often done using the technique of X-ray diffraction crystallography.III. Diffraction from a Crystala. When X-rays strike parallel planes of atoms or molecules in a crystal, constructiveinterference occurs if the difference in path length between beams reflected fromadjacent planes is an integral number of wavelengths.i. Constructive interference “adds” to the amplitude of the electromagnetic wave whereas destructive interference “subtracts” from the wave’s amplitude.b. Bragg’s law allows scientists to determine the distance between layers of atoms or molecules in a crystal lattice.i. nλ = 2d sin θIV. Crystal Latticea. When allowed to cool slowly, the particles in a liquid will arrange themselves to give the maximum attractive forces.i. Therefore, they minimize the energy.ii. The result will generally be a crystalline solid.b. The arrangement of the particles in a crystalline solid is called the crystal lattice.c. The smallest unit that shows the pattern of arrangement for all the particles is called the unit cell.d.V. Unit Cellsa. Unit cells arei. three-dimensional; usually containing two or three layers of particles;ii. repeated over and over to give the macroscopic crystal structure of the solid.b. Starting anywhere within the crystal results in the same unit cell.c. Each particle in the unit cell is called a lattice point.d. Lattice planes are planes connecting equivalent points in unit cells throughout the lattice.VI. Unit Cellsa. The number of other particles each particle is in contact with is called its coordination number.i. For ions, it is the number of oppositely charged ions an ion is in contact withb. Higher coordination number means more interaction; therefore, stronger attractive forces hold the crystal together.c. The packing efficiency is the percentage of volume in the unit cell occupied by particles.i. The higher the coordination number, the more efficiently the particles arepacking together.VII. Cubic Unit Cellsa. All 90° angles between corners of the unit cellb. The length of all the edges is equal.c. If the unit cell is made of spherical particles,i. ⅛ of each corner particle is within the cube;ii. ½ of each particle on a face is within the cube; iii. ¼ of each particle on an edge is within the cube.VIII. Cubic Unit Cells: Simple Cubica. Eight particles, one at each corner of a cubei. ⅛ of each particle lies in the unit cell.ii. Each particle part of eight cellsiii. Total = one particle in each unit cell1. 8 corners × ⅛b. Edge of unit cell = twice the radiusc. Coordination number of 6IX. Cubic Unit Cells: Body-Centered Cubica. Nine particles, one at each corner of a cube and one in centeri. ⅛ of each corner particle lies in the unit cell.1. Two particles in each unit cella. 8 corners × ⅛ b. + 1 centerb. Edge of unit cell = (4r) times the radius of the particlec. Coordination number of 8X. Cubic Unit Cells: Face-Centered Cubica. 14 particles, one at each corner of a cube and one on the center of each facei. ⅛ of each corner particle and ½ of face particle lie in the unit cell1. 4 particles in each unit cell2. 8 corners × ⅛ 3. + 6 faces × ½ XI. Classifying Crystalline Solidsa. Crystalline solids are classified by the kinds of particles found.b. Some of the categories are subclassified by the kinds of attractive forces holding the particles