Ch. 24 - Materials Flashcards
What is a crystal?
A crystal is a solid whose atoms, ions or molecules are arranged in a regular 3-D structure.
What are the 4 different types of crystals?
Ionic, molecular(polar and non-polar), metallic and covalent macromolecular.
Give examples of the different types of crystals.
Ionic: NaCl
Molecular(non-polar): I, (polar): Ice
Metallic: Na
Covalent macromolecular: diamond and graphite
What are the binding forces for the 4 different crystals?
Ionic: ionic bonds
Molecular(non-polar): van der Waals; forces, (polar): van der Waals’ forces and dipole-dipole interactions OR H bonds
Metallic: metallic bond
Covalent macromolecular: covalent bonds(sometimes van der Waals’ forces as well)
What causes diamond’s hardness and high melting point?
The atoms in diamond’s structure are arranged tetrahedrally and are covalently bonded.
Describe the solubility of the various crystals.
Ionic: usually in polar solvents
Molecular: depends on type
Covalent macromolecular: insoluble
Metallic: insoluble, except Hg
What are allotropes?
Allotropes are different physical forms of the same element.
What makes graphite soft and ideal for use as a lubricant?
Graphite is made of giant 2-D molecules, held together by van der Waals’ forces. The forces are strong enough to hold the molecule together but too weak to prevent them from sliding over each other if a force is applied. Making graphite soft and ideal as a lubricant.
What makes graphite a good conductor of electricity?
C atoms in the planar molecules of graphite use 3 valence electrons to form sigma bonds with 3 neighbouring atoms. The remaining electrons form a delocalised pi bond and are free to move if a voltage is applied.
Give the formula for buckminsterfullerene.
C60
Who developed the use of diffraction patterns to work out the structure of crystals?
William and Lawrence Bragg used these methods to work out the structure of NaCl, won a Nobel prize for it.
Who won the Nobel prize for using X-ray crystallography to determine the structure of penicillin?
Dorothy Hodgkin, she went on the work out the structure for vitamin B12.
What is a polymer?
A polymer is a large molecule made up of many identical repeating units called monomers.
What are the raw materials for polymers and how do they form polymers?
Alkenes are the raw materials. Addition polymerisation is used to form polythene, a polymer.
Why are metallic crystals good conductors of electricity?
Valence electrons are free to move through the crystal. This movement of electrons forms positive ions. Each ion is attracted to the delocalised electron cloud that surrounds them, causing metal to have a high melting point, be malleable and ductile.
