The Modern Periodic Table

1. The Modern Periodic Table name & atomic weight Carbon 12.011

2. “The properties of the elements are periodic functions of atomic number.” Law of Periodicity Group Period Similar chemical properties Repetition of properties Nonmetals – insulators not ductile Metalloids - Semiconductors Ductile ? Metals – Conducting, Ductile

3. Crystalline Solids Crystalline solids: Metals, ions, atoms, molecules Constructed form crystal lattices. Stabilized by electrostatic forces. Identical building blocks : unit cells. LATTICE:

4. X-ray Diffraction X-ray diffraction is used to study crystalline solids The lattice of regularly repeating atoms with spacing acts as a diffraction grating for the rays. The diffraction pattern is used to establish the structure of the solid!

5. Amorphous Solids Amorphous solids: disorderedsolids Strongly resemble liquids in this lack of long-range order Many amorphous solids can be thought of very accurately as frozen liquids. Common examples of amorphous solid are glass, candy (sugar), plastics. In all, there are then 5 categories of solids, 4 types of crystalline + amorphous

6. Summary of the Structures and Properties of Various Types of Solid Substances

7. Semicrystalline Materials Contain both amorphous and crystalline regions => strong and flexible. Examples: Plastics (polymers), Steel, Wood (cellulose), collagen (tendon)

8. Example: Polyvinylidenedifluoride PVDF is semicrystalline - Similar to Teflon (-CF2-CF2-) …-CH2-CF2-CH2-CF2-….. It has several different crystal phases, which can be modified by processing methods. The alpha phase is non-polar The beta phase is polar PVDF can be processed to contain mostly the polar form, by stretching the film to several time its original length

9. Electrical Properties of Semicrystalline Materials Semicrystalline materials respond to heat, pressure and external fields. They are used as heat and pressure sensors Thin films can be prepared than have a permanent electric filed across them. These are used as non-stick coatings, selective membranes, etc Electropoledfilms are used by theelectronicsindustry, ex. speaker membranes

10. Lattices and Closest Packing How do objects naturally arrange themselves? If a second layer is added how does that effect the arrangements? OR Non-closest Closest

11. Lattices and Unit Cells Mathematicians have shown that there are seven basic geometries in which unit cells can be assembled that completely fill 3-D space. These are called the seven crystal systems We will focus only on the cubic and the hexagonal crystal systems as they describe the vast majority of metallic elements.

12. Unit Cells LATTICE: Identical building blocks : unit cells. i) No “gaps” between them in the lattice. ii) All have same orientation in the lattice. iii) Cannot be arranged in a staggered fashion in the lattice. OR: OR: NOT:

13. Lattices and Unit Cells Consider the smallest possible “unit cell” : The smallest unit cell in a lattice is called the primitive unit cell. In general one would have to consider three-dimensions.

14. Closest Packing The marbles adopted a “closest packing” as in most metals. Two kinds: cubic closest packed hexagonal closest packed. The difference arises when a third row is added:

15. Hexagon Closest Packing Orient the lattice so that the layers are more easily seen: Note every second layer are superimposable, as shown in the case of the red layers. A B A

16. Cubic Closest Packing A B C A Every third layer is superimposible. Note that, there is an atom at each corner of the cube And, the center of each face. It is also called face centered cubic (fcc).

17. Cubic Lattices There are three types of cubic unit cells: Note in some cases only parts of an atoms is contained by the unit cell. i.e. The unit cell only contains the fraction of each atom that is *inside* the cube!

18. Lattices and Unit Cells

19. Co-ordination Number, Density and Metallic Radii The number of atoms an atom contacts in the lattice is referred to as its co-ordination number. Determine the coordination number of the following lattices: Simple cubic (e.g. Po) Face-centered cubic (e.g. Cu) Body-centered cubic (e.g. Na) Hexagonal closest packed (e.g. Mg) Lattice type is related to density. What is the relative order of density from most to least dense? How would you measure the density of a metal? How could you relate the lattice type and density to the atomic radius?

20. EXERCISE 1. Aluminum has a density of 2.699 g· cm–3, and the atoms are packed into a face-centered cubic unit cell. Use this information to find the radius of an aluminum atom. Along the face diagonal, there are two half and one whole sphere The diagonal length is (a2 + a2)1/2 and corresponds to 4 atomic radii

21. EXERCISE 2) Lithium has a metallic radius of 152 pm and the atoms are packed into a body-centered cubic unit cell. Calculate the density of lithium.

22. Cubic Lattices Lattice Packing fraction Density (m/r3) simple cubic 0.5236 0.125 body-centered cubic 0.6802 0.162 face-centered cubic 0.7405 0.177

23. Lattices, Density and Metallic Radii Europium has a metallic radius of 198.4 pm and a density of 5.243 g/cm3. Which cubic units cell is the likely for this crystal structure?