Advanced Chemistry Notes

Solids Recall: according to the Kinetic Theory (KT), solids were a state of matter where the AF dominated the KE of particles.

Types of Solids Amorphous Solids: rigid solid without any definite shape or crystalline structure Particles are trapped in a disordered arrangement Sometimes called super-cooled liquids Random molecular arrangement is often due to rapid cooling EX: rubber, glass, several plastics

Amorphous Solid

Types of Solids Crystalline solids: solids where particles exist in highly ordered arrangements Most jewelry is crystalline Unit cell – smallest repeatin’ unit of a crystall; its building block The unit cell will look like a miniature form of the crystal

Crystalline Solids

Types of Unit Cells Simple Cubic (SCC) – atoms are arranged at corners of an imaginary cube Body Centered Cubic (BCC) – atoms are arranged at corners and center of cube Face Centered (FCC) – atoms are arranged at each face of the cube

Types of Unit Cells

Atoms are shared by unit cells Simple Cubic (SC) 8 (1/8) atoms Body Centered Cubic (BCC) 8 (1/8) atoms + 1 full atom in center Face Centered (FCC) 6 (1/2) atoms + 8 (1/8) atoms

The Unit Cell Information the unit cell enables us to find: Mass of unit cell Volume of unit cell Length of side of unit cell Surface area of unit cell

The Unit Cell Example: Chromium First determine # of atoms in the unit cell Ex: How many atoms are in Cr unit cell 2 atoms Convert atoms to moles 2 atoms Cr 1 mole Cr = 3.32 X mol X 10 23

The Unit Cell Example: Chromium Convert mol Cr to grams 3.32 X mol 52g Cr = 1.73 X g 1 mol Cr Use Cr’s density (7.19 g/cm 3 ) to find volume 7.19 g/cm3 = 1.73 X g / V V = 2.4 X

The Unit Cell Example: Chromium Cube root volume to find length of sides Cube root (2.4 X ) l = X Square length to find surface area (2.887 X ) 2 Surface area = 5 X cm 2

Crystalline Solids Compound unit cells Ex: Sodium Chloride Sodium Chloride is considered a face centered cubic compound unit cell

Crystalline Solids Crystal structures of an ionic solid like NaCl are determined primarily by the ratio of radii of the ions. Positive ions must be large enough to keep the negative ions from coming into contact with each other. Positive ions also have to be small enough from coming into contact with themselves.

Crystalline Solids Most compounds from the alkali metals and the halogens produce crystals with compound unit cells like salt except one. Cesium Chloride – behaves differently because Cs is a large atom. Cesium atoms in CsCl are surrounded by eight atoms of chlorine instead of six.

Crystalline Solids Unit Cells that repeated over and over in a definite geometric arrangement are called crystal lattices. Crystal lattices make up crystal systems. There are seven Crystal systems (see p. 398 table 16.1) Cubic Tetragonal Hexagonal Rhombohedral Orthorhombic Monoclinic Triclinic Different unit cells can make up the same crystal system. This allows for fourteen different combinations. See table 16.2 on p. 399.

Crystal Lattices

Crystal Systems

Crystals Summary How does the KT define Solids? What is the difference between amorphous and crystalline solids? Crystals are made up of Unit cells. What are the three basic types of unit cell? How are crystalline solids organized? Unit cell  crystal lattice  crystal system