Types of Crystals Shapes and Structures

Theres more than one way to categorize a crystal. The two most common methods are to group them according to their crystalline structure and to group them according to their chemical/physical properties. Crystals Grouped by Lattices (Shape) There are seven crystal lattice systems.   Cubic or Isometric: These are not always cube-shaped. Youll also find octahedrons (eight faces) and dodecahedrons (10 faces).Tetragonal: Similar to cubic crystals, but longer along one axis than the other, these crystals forming double pyramids and prisms.Orthorhombic: Like tetragonal crystals except not square in cross-section (when viewing the crystal on end), these crystals form rhombic prisms or dipyramids (two pyramids stuck together).Hexagonal:  When you look at the crystal on end, the cross-section is a six-sided prism or hexagon.Trigonal: These crystals  possess a single 3-fold axis of rotation instead of the 6-fold axis of the hexagonal division.Triclinic:  These crystals are not usually symmetrical from one side to the other, which can lead to some fairly strange shapes.Monoclinic: Like skewed tetragonal crystals, these crystals often form prisms and double pyramids. This is a very simplified view of crystal structures. In addition, the lattices can be primitive (only one lattice point per unit cell) or non-primitive (more than one lattice point per unit cell). Combining the 7 crystal systems with the 2 lattice types yields the 14 Bravais Lattices (named after Auguste Bravais, who worked out lattice structures in 1850). Crystals Grouped by Properties There are four main categories of crystals, as grouped by their chemical and physical properties. Covalent Crystals:  A covalent crystal has true  covalent bonds between all of the atoms in the crystal. You can think of a covalent crystal as one big molecule. Many covalent crystals have extremely high melting points. Examples of covalent crystals include diamond and zinc sulfide crystals.Metallic Crystals:  Individual metal atoms of metallic crystals sit on lattice sites. This leaves the outer electrons of these atoms free to float around the lattice. Metallic crystals tend to be very dense and have high melting points.Ionic Crystals:  The atoms of ionic crystals are held together by  electrostatic forces (ionic bonds). Ionic crystals are hard and have relatively high melting points. Table salt (NaCl) is an example of this type of crystal.Molecular Crystals:  These crystals contain recognizable molecules within their structures. A molecular crystal is held together by non-covalent interactions, like van der Waals forces or  hydrogen bonding. Molecular crystals tend to be soft with relatively low melting points. Rock candy, the crystalline form of table sugar or sucrose, is an example of a molecular crystal. Crystals may also be classified as piezoelectric or ferroelectric. Piezoelectric crystals develop dielectric polarization upon exposure to an electric field. Ferroelectric crystals become permanently polarized upon exposure of a sufficiently large electric field, much like ferromagnetic materials in a magnetic field. As with the lattice classification system, this system isnt completely cut-and-dried. Sometimes its hard to categorize crystals as belonging to one class as opposed to another. However, these broad groupings will provide you with some understanding of structures. Sources Pauling, Linus (1929). The principles determining the structure of complex ionic crystals. J. Am. Chem. Soc. 51 (4): 1010–1026. doi:10.1021/ja01379a006Petrenko, V. F.; Whitworth, R. W. (1999). Physics of Ice. Oxford University Press. ISBN 9780198518945.West, Anthony R. (1999). Basic Solid State Chemistry (2nd ed.). Wiley. ISBN 978-0-471-98756-7.

Life Span Development and Personality Essay Questions

Life Span Development and Personality Essay Questions Cathy Perry Psy 300 September 27, 2010 Tara Terry Ph.D. Select a famous individual from the 20th or 21st centuries: Maya Angelou (born as Marguerite Ann Johnson). Conduct research concerning the background of your selected individual to determine what forces have impacted his or her life from the viewpoint of developmental psychology. 1. Discuss the influences of heredity and environment (including family and social support) on your individual’s psychological development. Be sure to describe specific areas of psychological development (moral, emotional, etc.). (300-500 words). Maya Angelou was born in St. Louis, Missouri in 1928. At the age of three, she and her†¦show more content†¦The Psychodynamic theory can be applied to Maya Angelou in several areas. One of these areas was the continuous moves from parents to grandparents throughout her childhood. The consistency she had as a child was her grandmother in Stamps, Arkansas. Maya and her brother had love, stability and the meaning of family while they lived with her. According to Kowalski and Westen, (2009), Disrupted attachments are associated with severe personality disturb ances, depression, antisocial behavior and adjustment problems†¦, and childhood experiences such as parental neglect or even parental divorce cause more vulnerability to adult insecurities. Psychodynamic theorists state that depressive behaviors have various causes, one of which would be a parental attachment history influencing problems and fears of rejection and or abandonment. Both Maya and her brother had problems dealing with the thoughts of abandonment. Maya thought it was better to think of them being dead than to imagine having parents that did not want their children (Mongeau-Marshall, 1994). Maya was a rape victim at a very early age that traumatized her into speechlessness for five years. The fact that she was only eight years old is enough reason for her to have trust issues. According to Mongeau-Marshall, (1994) Maya trusted Mr. Freeman and felt him to be a father figure. After his death, she stopped talking to everyone but her brother, which in a psychodynamic theory viewpoint the psychological thoughtShow MoreRelatedDefinition Of Humanity In Blade Runner840 Words   |  4 PagesThe film that will be thoroughly analysed throughout this essay is ‘Blade Runner’ which is based on the novel ‘Do Androids Dream of Electric Sheep?’. This film was produced by Ridley Scott, who explores how replicants associate in human society. The creators of the desirable replicants display a company slogan that reads ‘More human than human’. The concept and definition of this will be thoroughly analysed throughout this essay and its relation to the characters will be stated. 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Evaluate strategies for developing and maintaining positive working relationships free essay sample

How to develop relationships with children and staff and why it is important Communicating effectively within the childcare setting is very important to enable strong relationship to build between colleagues, children and parents. Staff communicating positively with colleagues is an important part in helping build a strong and trusting relationship with each other. Developing close relationships with the other staff will help to inform each other of any worries or concerns that one of you may have regarding a child. It can also encourage conversation regarding any ideas or thoughts you may have regarding activities. It’s important to develop a good relationship with staff as it will create a positive environment for both children and staff. This will help to develop a calm, happy and relaxed atmosphere creating a positive environment for teaching. Children Developing positive relationships with the children is the main key to a happy and calm environment. We will write a custom essay sample on Evaluate strategies for developing and maintaining positive working relationships or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page Without a positive and supportive attitude there will be no trust and honesty between yourself and the children. They will not feel like they can talk to you which may mean they could be keeping something important inside, which could affect their learning or social skills. With good communication from the practitioners, children can effectively engage in goal setting and problem solving which could enhance their ability to learn. It is important to be consistent in your behaviour and relationships so that children learn to do this, we as practitioners need to model the kind of behaviour we expect from them. Parents It important to build a relationship with parents an easy way to do this is to make sure you have good communication with them. For example make sure that you talk them in the appropriate language for example using their manners for example, please and thank you. Therefore if you have good commutation skills and good body language when working with parents they are more likely to trust you when looking after their children. Children who can sense that their main carer has a good relationship with the childcare setting are more likely to be happy being left in the setting. Other way’s that you can build relationships with parent’s are that you would have regular contact with them for the best interests of the child. It is also important when building a relationship with parents that you understand what they think is best for the child, and if they need advice you should give them or try to find out for them.