1. The Periodic Table Dmitri Mendeleev, In 1869, noticed that elements exhibited similar behaviour, in groups, in the ratios in which they form molecules with H and O. Elements arranged by increasing mass so that similar elements form columns Incomplete – noble gases are missing Blank spaces left for elements yet to be discovered. In 1913, H.G.J. Moseley- the periodic table is more descriptive if the elements were in order of increasing atomic number rather than increasing mass. Order based on atomic mass causes misalignments.

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

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

4. 4 Crystalline Solids Crystalline solids: Metals, ions, atoms, molecules Constructed form crystal lattices. Stabilized by electrostatic forces. Identical building blocks : unit cells. LATTICE:

5. 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! X-ray Diffraction

6. Amorphous Solids Amorphous solids: disordered solids 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

7. TypeExamplesStructural UnitsTypical Properties IonicNaCl, K 2 SO 4, CaCl2, (NH 4 ) 3 PO 4 Positive and negative ions Hard; brittle; high melting point; electric conductivity poor as solid & good as liquid; often water-soluble MetallicIron, silver, copper, other metals & alloys Metal cations in a sea of electrons Malleable; ductile; wide range of hardness and melting points; good electric conductivity in solid & liquid; good heat conductivity. MolecularH 2, O 2, I 2, H 2 O, CO 2, CH 4, CH 3 OH, CH 3 CO 2 H MoleculesSoft; low to moderate melting points & boiling points; poor electric conductivity in solid and liquid NetworkGraphite, diamond, quartz, feldspars, mica AtomsWide range of hardnesses & melting points (3-dimensional bonding > 2- dimensional bonding > 1-dimensional bonding); poor electric conductivity, with some exceptions Amorphous (glassy) Glass, polyethylene, nylon Molecules, ions No long range order Soft, wide temperature range for melting; poor electric conductivity, with some exceptions Summary of the Structures and Properties of Various Types of Solid Substances

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

9. Example: Polyvinylidenedifluoride …-CH 2 -CF 2 -CH 2 -CF 2 -….. PVDF is semicrystalline - Similar to Teflon (-CF 2 -CF 2 -) 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

10. 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 Electropoled films are used by theelectronics industry, ex. speaker membranes

11. 11 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

12. 12 Lattices and Unit Cells We will focus only on the cubic and the hexagonal crystal systems as they describe the vast majority of metallic elements. 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

13. 13 Unit Cells 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. LATTICE: NOT: OR:

14. 14 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.

15. 15 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:

16. 16 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. ABAABA

17. 17 Cubic Closest Packing 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). ABCAABCA

18. 18 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!

19. 19 Lattices and Unit Cells

20. 20 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?

21. 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. EXERCISE Along the face diagonal, there are two half and one whole sphere The diagonal length is (a 2 + a 2 ) 1/2 and corresponds to 4 atomic radii

22. 22 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. EXERCISE

23. 23 Cubic Lattices Lattice Packing fraction Density (m/r 3 ) simple cubic0.52360.125 body-centered cubic0.68020.162 face-centered cubic0.74050.177

24. 24 Lattices, Density and Metallic Radii Europium has a metallic radius of 198.4 pm and a density of 5.243 g/cm 3. Which cubic units cell is the likely for this crystal structure?