CHM2 11_12 Q3 0106 PF FD.pptx

Lesson 1.6 Types and Properties of Crystalline Solids General Chemistry 2 Science, Technology, Engineering, and Mathematics Crystalline solids have different types and properties. 2 Crystalline solids are arranged in a definite repeati...

Lesson 1.6 Types and Properties of Crystalline Solids General Chemistry 2 Science, Technology, Engineering, and Mathematics Crystalline solids have different types and properties. 2 Crystalline solids are arranged in a definite repeating pattern held together by uniform, strong intermolecular forces. 3 Their use can be explained by their type and properties. Just like steel is used in infrastructure, while diamonds are not. 4 What are the different types and properties of crystalline solids? 5 Learning Competency At the end of the lesson, you should be able to do the following: Describe the difference types of crystals and their properties: ionic, covalent, molecular, and metallic solids (STEM_GC11IMF-IIIa-c-105). 6  Learning Objectives At the end of the lesson, you should be able to do the following: Describe the unit cell. Enumerate and discuss the types and properties of crystalline solids. 7  Unit Cell Unit Cell the small repeating unit in the structure of crystalline solids composed of lattice points that represent the locations of ions or atoms stacking them repeatedly in all three dimensions = crystal structure 8  Unit Cell Crystal Lattice the arrangement of the geometrical patterns of points in the unit cell Motif an atom or a group of atoms that is repeated at each lattice point to generate a crystal structure 9  Unit Cell For 2D lattice the unit cell: parallelogram ○ two lattice vectors (a and b) four (4) primitive lattices for 2D ○ where the lattice points are located only at the corners of the unit cell ○ square, rectangular, hexagonal, and oblique 10  Unit Cell For 3D lattice the unit cell: parallelepiped ○ three lattice vectors (a, b, and c) ○ three lattice angles (α, β, and γ) seven (7) primitive lattices for 3D ○ cubic, hexagonal, tetragonal, rhombohedral, orthorhombic, monoclinic, and triclinic 11 Unit Cell The seven three-dimensional primitive lattices 12  Unit Cell Cubic Lattice a = b = c; α = β = γ primitive cubic lattice - lattice points at all corners of the cube body-centered cubic lattice - an additional lattice point placed at the center of a cubic unit cell face-centered cubic lattice - an additional 13 Unit Cell The primitive cubic lattice (left), the body-centered cubic lattice (center), and the face-centered cubic lattice (right) 14 What are the different types and properties of crystalline solids? 15  Types of Crystalline Solids Crystalline Solids classified according to the type of forces that hold its particles together four (4) main types ○ metallic ○ covalent network ○ molecular ○ ionic 16  Types of Crystalline Solids Metallic Solids/Metals consist entirely of metal atoms strong bonding due to dispersion forces, yet not enough valence electrons to form covalent bonds between atoms metallic bonding - a uniform distribution of atomic nuclei within a “sea” of delocalized electrons 17  Types of Crystalline Solids Metallic Solids/Metals adopt structures with symmetric close- packed arrangements of atoms Copper is a metallic solid. examples: sodium metal and copper 18  Types of Crystalline Solids Metallic Solids/Metals properties: ○ high electrical and thermal conductivity ○ malleable ○ ductile ○ melting points vary widely 19 Why is pure gold not suitable for making jewelry? 20  Types of Crystalline Solids Covalent Network Solids made up of atoms held together by a network of covalent bonds can be made of one of more different atoms valence electrons of atoms are used to form covalent bonds 21  Types of Crystalline Solids Covalent Network Solids poor conductors typically characterized by strength, hardness, and high melting points examples: diamond and graphite 22  Types of Crystalline Solids Covalent Network Solids diamond ○ made up of carbon atoms ○ hardest known material ○ 3D crystals ○ good thermal conductor Diamond is an allotrope of carbon. 23  Types of Crystalline Solids Covalent Network Solids graphite ○ made up of carbon atoms ○ 2D covalent network solid ○ can form flat sheets ○ good electrical conductor Graphite is an allotrope of carbon that is soft and used as a solid 24  Types of Crystalline Solids Allotropy the ability of a single element, atom, or molecule to form multiple structures of Diamond and graphite are allotropes of carbon. solids 25 Remember Although the majority of the covalent network solids have poor conductivity, graphite is considered a good conductor. 26  Types of Crystalline Solids Molecular Solids made up of covalently bonded atoms or molecules that are held together by intermolecular forces such as van der Waals valence electrons are used in bonding poor conductors (insulators) soft 27  Types of Crystalline Solids Molecular Solids the strengths of attractive forces between units vary widely ○ example: melting points Molecular Solid Melting Point ice 0 OC sugar 186 OC fullerene 280 OC 28  Types of Crystalline Solids Molecular Solids most are nonpolar molecular solids with permanent dipoles (polar molecules) ○ melt at a higher temperature ○ easily dissolve in water ○ example: sugar 29  Types of Crystalline Solids Ionic Solids composed of positive (cation) and negative (anions) ions that are held together by electrostatic attractions difficult to break Sodium chloride (NaCl) high melting points is an example of an ionic solid. 30  Types of Crystalline Solids Ionic Solids electrostatic attractions in ionic solids are stronger compared to van der Waals forces in molecular solids poor conductors ○ ions are unable to move in solid form ○ conducting when molten or dissolved as their ions are free to move 31  Check Your Understanding Write T if the following statement is true. Otherwise, write F. 1. The three-dimensional unit cell is characterized by three lattice vectors. 2. Ionic solids have high melting points. 3. Molecular solids tend to be hard and exhibit a high melting point. 32  Let’s Sum It Up! The unit cell is a small repeating unit that makes up the structure of a crystalline solid. The crystal lattice is the arrangement of the geometrical patterns of points in the unit cell. 33  Let’s Sum It Up! There are four types of crystalline solids. ○ Metallic solids - simply known as metals consist entirely of metal atoms. The atoms are held together by a unique bonding called metallic bonding. ○ Covalent network solids - made up of atoms that are held together by a network of covalent bonds. 34 Let’s Sum It Up! ○ Molecular solids - are made up of covalently bonded atoms or molecules that are held together by intermolecular forces such as van der Waals. ○ Ionic solids - are composed of positive (cation) and negative (anion) ions that are held together by electrostatic attractions. 35 Challenge Yourself Why do polar molecular solids have higher melting points than nonpolar molecular solids? 36 Bibliography Brown T.L. et al. 2012. Chemistry: The Central Science. Pearson Prentice Hall.Brown. Chemistry: The Central Science. Prentice-Hall, 2005. Bettelheim, Frederick A., et al. 2015. Introduction to General, Organic and Biochemistry. Boston: Cengage Learning. Ebbing, Darrell and Steven Gammon. 2016. General Chemistry. Boston: Cengage Learning. Moore, John W, and Conrad L. Stanitski. 2015. Chemistry: The Molecular Science, 5th ed. USA: Cengage Learning. Petrucci, Ralph H. General Chemistry: Principles and Modern Applications. Toronto, Ont.: Pearson Canada, 2011. Print. 37