The Carbon Chemistry and Crystal Structure of Diamonds

The word diamond is derived from the Greek word adamao, meaning I tame or I subdue or the related word adamas, which means hardest steel or hardest substance. Everyone knows diamonds are hard and beautiful, but did you know a diamond could be the oldest material you might own? While the rock in which diamonds are found may be 50 to 1,600 million years old, the diamonds themselves are approximately 3.3 billion years old. This discrepancy comes from the fact that the volcanic magma that solidifies into rock, where diamonds are found did not create them, but only transported the diamonds from the Earths mantle to the surface. Diamonds also may form under the high pressures and temperatures at the site of meteorite impacts. The diamonds formed during an impact may be relatively young, but some meteorites contain stardust — debris from the death of a star — which may include diamond crystals. One such meteorite is known to contain tiny diamonds over 5 billion years old. These diamonds are older than our solar system. Start with Carbon Understanding the chemistry of a diamond requires a basic knowledge of the element carbon. A neutral carbon atom has six protons and six neutrons in its nucleus, balanced by six electrons. The electron shell configuration of carbon is 1s22s22p2. Carbon has a valence of ​four since four electrons can be accepted to fill the 2p orbital. Diamond is made up of repeating units of carbon atoms joined to four other carbon atoms via the strongest chemical linkage, covalent bonds. Each carbon atom is in a rigid tetrahedral network where it is equidistant from its neighboring carbon atoms. The structural unit of diamond consists of eight atoms, fundamentally arranged in a cube. This network is very stable and rigid, which is why diamonds are so very hard and have a high melting point. Virtually all carbon on Earth comes from the stars. Studying the isotopic ratio of the carbon in a diamond makes it possible to trace the history of the carbon. For example, at the earths surface, the ratio of isotopes carbon-12 and carbon-13 is slightly different from that of stardust. Also, certain biological processes actively sort carbon isotopes according to mass, so the isotopic ratio of carbon that has been in living things is different from that of the Earth or the stars. Therefore, it is known that the carbon for most natural diamonds comes most recently from the mantle, but the carbon for a few diamonds is the recycled carbon of microorganisms, formed into diamonds by the earths crust via plate tectonics. Some minute diamonds that are generated by meteorites are from carbon available at the site of impact; some diamond crystals within meteorites are still fresh from the stars. Crystal Structure The crystal structure of a diamond is a face-centered cubic or FCC lattice. Each carbon atom joins four other carbon atoms in regular tetrahedrons (triangular prisms). Based on the cubic form and its highly symmetrical arrangement of atoms, diamond crystals can develop into several different shapes, known as crystal habits. The most common crystal habit is the eight-sided octahedron or diamond shape. Diamond crystals can also form cubes, dodecahedra, and combinations of these shapes. Except for two shape classes, these structures are manifestations of the cubic crystal system. One exception is the flat form called a macle, which is really a composite crystal, and the other exception is the class of etched crystals, which have rounded surfaces and may have elongated shapes. Real diamond crystals dont have completely smooth faces but may have raised or indented triangular growths called trigons. Diamonds have perfect cleavage in four different directions, meaning a diamond will separat e neatly along these directions rather than break in a jagged manner. The lines of cleavage result from the diamond crystal having fewer chemical bonds along the plane of its octahedral face than in other directions. Diamond cutters take advantage of lines of cleavage to facet gemstones. Graphite is only a few electron volts more stable than diamond, but the activation barrier for conversion requires almost as much energy as destroying the entire lattice and rebuilding it. Therefore, once the diamond is formed, it will not reconvert back to graphite because the barrier is too high. Diamonds are said to be metastable since they are kinetically rather than thermodynamically stable. Under the high pressure and temperature conditions needed to form a diamond, its form is actually more stable than graphite, and so over millions of years, carbonaceous deposits may slowly crystallize into diamonds.

Hesss Law Definition - Chemistry Glossary

Hesss law states that the energy change in an overall chemical reaction is equal to the sum of the energy changes in the individual reactions comprising it. In other words, the enthalpy change of a chemical reaction (the heat of reaction at constant pressure) does not depend on the pathway between the initial and final states. The law is a variation of the first law of thermodynamics and conservation of energy. Importance of Hesss Law Because Hesss law holds true, its possible to break a chemical reaction into multiple steps and use the standard enthalpies of formation to find the overall energy of a chemical reaction. Standard enthalpy tables are compiled from empirical data, usually acquired using calorimetry. Using these tables, its possible to calculate whether or not a more complex reaction is thermodynamically favorable or not. Applications of Hesss Law In addition to calculating the enthalpy of a reaction rather than directly measuring it, Hesss law is used to: Find electron affinities based on theoretical lattice energy.Calculate heat change of phase transitions.Calculate heat change when a substance changes allotropes.Find the heat of formation of an unstable intermediate in a reaction.Find the lattice energy of ionic compounds. Sources Chakrabarty, D.K. (2001). An Introduction to Physical Chemistry. Mumbai: Alpha Science. pp. 34–37. ISBN 1-84265-059-9.Leicester, Henry M. (1951). Germain Henri Hess and the Foundations of Thermochemistry. The Journal of Chemical Education. 28 (11): 581–583. doi:10.1021/ed028p581

Cry the Beloved Country, Inherit the Wind, Julius Caesar Free Essays

Eleanor Roosevelt stated that people make their own decisions, and the reasoning behind what happens in their lives is of their own responsibility and consequence. Bert Cates, from Jerome Lawrence’s Inherit the Wind, applies directly to this statement while Stephen Kumalo of Cry the Beloved Country and Caesar of Julius Caesar do not. Stephen Kumalo and Julius Caesar’s lives were drastically influenced by the choices of others, not their own. We will write a custom essay sample on Cry the Beloved Country, Inherit the Wind, Julius Caesar or any similar topic only for you Order Now Bertram Cates, however, made his own decisions and influenced his life individually. In Inherit the Wind, Bert Cates illegally teaches evolution to his biology class. As a citizen of Hillsboro, TN, he must have known that teaching evolution was unlawful as well as the consequences that would follow. Cates, however, is a man who wants to fully educate his students and open them up to different ideas and perspectives. For this reason, he teaches evolution anyway and is prosecuted and fined $100 (Lawrence, . Inherit the Wind. Pg 103) for it. It’s a consequence of his choice to teach such a controversial subject and because of it his life is greatly impacted. In Julius Caesar, Julius’ fate was definitely not of his own choice. Brutus, Cassius, Cinna, Decius, and Casca, a group of people Caesar trusted, murder him. Caesar had done nothing wrong. He’s a bit cocky and self centered at times, perhaps, but he has done nothing harmful to the well-being of others. The lack of trust from Brutus, Cassius, Cinna, Decius, and Casca is why Caesar’s life is brought to an end. They think he’d go mad with power, so they take him out before he even has the chance to prove them right or wrong. In reality, he would have done what is right for his people, and that is apparent in his will. â€Å"To every Roman citizen he gives, to every several man, seventy-five drachmas. †, Marc Antony reads off of Caesar’s will, â€Å"Moreover, he hath left you all his walks, private arbors, and new-planted orchards, on his side Tiber. He hath left them to you and to your heirs forever. † (Shakespeare, Julius Caesar. Pg. 133) Caesar has no control over stopping the situation because he doesn’t even know it’s going to happen. He hasn’t done anything to deserve his murder, it’s not of his own consequence. He was killed out of the mistrust from others. Stephen Kumalo of Cry the Beloved Country is tossed around, put through so much pain, and none of it is of his doing. He may have made the decision to look for his son and sister to protect his family, but isn’t it a man’s instinct to care for the people who are closest to him? Stephen’s son made the decision to take the wrong path, live the life of a thief, and eventually kill another person. Stephen’s sister made the decision to sell alcohol, sleep around, and not care for her son. All of these bad choices were made by other people, yet Stephen was still strongly affected by them. Eleanor Roosevelt says that people are responsible for what happens in their lives, but Stephen couldn’t control Absalom being sentenced to death, Gertrude leaving, or his brother screwing him over. This is because he didn’t have the money, power, and most importantly, the control over their decisions. How to cite Cry the Beloved Country, Inherit the Wind, Julius Caesar, Essay examples