Monday, July 27, 2020

Dolphin Charms

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When people think of dolphins, they probably recall their cute faces, which look as if they are smiling at us, and amazing performances, which show their remarkable intelligence. When I look at a face of dolphin, I feel peace and tranquility even if it is just a picture. I have been fascinated by dolphins for years and decided to study marine biology at college, hoping that someday I could do some research on cetaceans to deepen knowledge of these marvelous creatures. However, I did not see dolphins as such special animals from the beginning. I love animals in general, and dolphins were just one of many cute and smart animals. It was a story that changed my attitude toward dolphins forever a story about a dolphin interacting with a child who suffered from autism.


Autistic people usually do not express their emotion nor hardly respond to what others say, so did not this child on TV. However, to my surprise the child actually smiled and showed eagerness for more physical interaction with a dolphin after the moment he swam with the dolphin. When I watched this story first, I was skeptical about that dolphins had a special power to heal people. But it is more or less true even though science can not give a complete explanation yet. It is now called dolphin-assisted therapy, and many case studies have shown evidently dolphins, especially by means of swimming with them, have a profound impact on those with disabilities (Blow 0; D'Aulaire and D'Aulaire 5).


This is how I was dragged into the dolphin world. After that, I read all kinds of books about dolphins from trustworthy scientific books to fantastic novels to dubious spiritual and healing books. I watched TV programs and movies and of course went to see these great creatures with my own eyes at aquariums and marine parks as well as in the wild. The more I knew about dolphins, the more mysterious I saw them. Then, I noticed there are so many others like me, fascinated with dolphins. And they are not only in Japan or the States but almost all over the world. There are also people to hold in awe of dolphins as god-like quantities, angels, holly spirits, or healers, and even some people identify them to extraterrestrials. Although dolphin popularity has explosively increased for last several decades as represented by a main attraction at marine parks and a character of popular TV series like ¡§Flipper,¡¨ yet interestingly this is not something that happened just today or yesterday. Dolphins often appear in mythology, folklore, legends, arts and other literatures. For thousands of years, dolphins have fascinated people with their gentleness and friendliness to men and human-like intelligence and as respect as animals living in ocean realm that we never know.


Men have kept a relationship with dolphins since the ancient era when they did not have any written languages to record the encounter with the animals. Instead, they told stories generations to generations, drew and curved their objects of interests on rocks and walls in caves.


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We now find hundreds of dolphin stories in many cultures around the world. Mark Carwardine, a conservation officer of the World Wild Fund for Nature in Britain, says that dolphins along with whales ¡§have long been the stars of mythology, folklore, religion, and most recently, popular entertainment¡¨ (). Unlike whales which had received bad reputations as sea monsters in the Bible and many other legends and folklore, dolphins have always been viewed as gentle and kind friends of humans (Carwardine 4-5).


Among many episodes on dolphins, ancient Greek mythology is definitely a classic. Greeks often associated dolphins with the gods and goddess. There is a legend in the Homeric hymns, which explains how dolphins were created and why they are so kind to humans. Antony Alpers, the author of the book, Dolphins The Myth and the Mammal, writes that the Greeks believed that dolphins were once men who plotted to abduct and sell Dionysos, the god of wine and frenzy (also known as Bacchus), as a slave in Asia. When Dionysos noticed their plot, he called on the divine power. Terrified pirates dove into the sea, then changed into dolphins. Since then, they became capable of doing no harm and were respected as a symbol of kindness and virtue in the sea (5-6; see also Stenuit 1). Alpers points out that this legend shows that ¡§the Greeks knew very well there was something different about dolphins, and that although they lived in the sea they were not the same as fish, but were in some way more like humans¡¨ (5). Therefore, they created this imaginative story as an expression of their affection and esteem towards dolphins.


As one can tell from the legend, dolphins were viewed as sacred fish with such a great respect by the Greeks. Thus, murder of a dolphin was considered equivalent to that of a man as Oppian declares in his long poem Halieutica


It is an offence to the Gods to hunt dolphins, and he can no longer approach the Gods to offer a sacrifice nor touch their altars with pure hands, who of his own will has been the cause of the destruction of dolphins. He makes impure even those living under his roof, because the Gods hold the massacre of the monarchs of the depths to be as execrable as the murder of a human. (qtd in Stenuit xv)


The Greeks' fascination and imagination for dolphins also created another form of dolphin Delphinus, a constellation in the sky. When Poseidon, the god of the sea (also known as Neptune), desired to get married with Amphitrite, she refused him and hid in Mount Atlas. He sent out many searchers, and it was Delphinus that found and brought her back to him. Poseidon eventually married Amphitrite and gave Delphinus the highest honors of placing its image in the sky (Alpers 5).


The stories above seem just fantasies created by people's imagination; however, there are many episodes based on stories thought to be true, which explain why dolphins were called friends of humans. In those stories, dolphins saved humans from drowning and protected from shark attack and rapid current. Alpers says that the most popular episode known today is probably the one about Arion, which was recorded later by an ancient historian Herodotos (6).


Arion was the greatest poet and musician of all Greeks in his time. When he was on the way to Corinth after he won at music competitions, the crew plotted to kill him to take his money. Although Arion begged them to take his money but not to kill him, they did not listen to him. Then, he asked them for a last wish to let him sing before dying. After he finished singing, he threw himself into the sea. However, a dolphin attracted to his beautiful music swam to him and carried safely onshore taking him on its back. The sailors were caught when arriving at the harbor, and Arion, in his gratitude, offered a bronze statue of a man riding on a dolphin to the temple at Tainaron. (Alpers 7-, see also Stenuit 5).


This story may also sound fiction, yet Robert Stenuit, the author of The Dolphin, Cousin to Man, claims that the same story was recorded by three dozens of Greek and Latin authors besides Herodotos (5). There are more trustworthy stories that dolphins rescue humans in the ocean, which have been told not only in ancient myths or legends but also in today's newspaper or magazines (Stenuit 1-1).


Dolphins are also known to have a great affinity to men and a compassion for the object of their affection. The stories that they made friends with humans especially boys have often been recorded. The Roman scholar Pliny the Elder wrote a story in Naturalis Historia. A child of Iasos, Hermias, made friends with a dolphin who carried him on its back, but one day a rapidly rising storm washed him off and he was drowned. The dolphin brought the body on the beach and lay down next to him to die. The people of Iaos concluded that the dolphin took responsibility and decided to share a death (cited in Alpers 1-1; cited in Stenuit 6-7). Although nobody knew if the dolphin had died indeed because of the reason that people thought, it was natural for the Greeks to think like that because they believed that dolphins were once men and that they kept the memory of it in their souls (Stenuit 16).


What interests me here is that not only Greeks and Romans viewed dolphins as special animals. Legends and folklore in other cultures also suggest that dolphins have been gentle friends of humans and sacred fish. They, like Greeks and Romans, somehow knew that dolphins were different from other animals, even though they hardly knew their nature. They are also fascinated with and esteemed the animals. Therefore, doing any harm to dolphins are thought to give rise to a bad luck or illness.


Michael Donoghue and Annie Wheeler report in their book, Save the Dolphins, that people in the Pacific have considered dolphins as messengers of the gods just like the Greeks and Romans. Ancestral spirits were thought to become guardian dolphins or sharks. An Australian Aborigine tribe, known as ¡§the Dolphin People,¡¨ is said that they have been able to communicate with the wild bottlenose dolphins for centuries. And there are some people on different islands, who have the power to call dolphins (-).


There have been many records of a mutual relationship between dolphins and fishermen, often found in Mediterranean and Australia and along livers in Amazon, China, and India. Stenuit describes that dolphins assisted fishermen chasing fish towards the land or the net, and the fishermen gave a share of the fishing to the animals in gratitude (154-157).


Besides telling stories, dolphins have been described in many forms of arts and crafts by the artists who were fascinated and inspired by them. Carwardine indicates that the ancient Greeks and Romans used figures of dolphins for cups, mosaics, sculptures, and decorations of the launches. They often engraved coins with the image of a boy riding on a dolphin, which is based on the episodes in myths and legends (4). Other dolphin sculptures and paintings have been found over the world where the stories have also been told (Iruka Kujira Odyssey 5).


Most recently, dolphins are found everywhere such as on paintings, T-shirts, and coffee mugs (Mager ). The painters of dolphins and whales such as Christian Riese Lassen and Wyland have earned their fame and a great profit. Seth Lubove, a writer of the Forbes magazine, states that those artists gained more than 100 million of the annual retail sales from their paintings and other products with the figures of dolphins and whales (17). This trend surely infers that dolphin popularity is extremely high.


While people were telling the stories about dolphins and drawing them, Alpers writes that there were some people who focused on the observation of the dolphin's nature and behavior. They rather sought the scientific explanation of things than just the stories and imagination. The first cetologist was the Greek philosopher and scientist Aristotle. He recorded his observations and discoveries in his Historia Animalium (0).


Aristotle clearly distinguished dolphins from fish. He knew that although they are living in the ocean, dolphins are warm-blooded and air-breathing mammals just like human beings. He knew that mothers bear a calf instead of laying eggs like fish and nourish them with milk. His investigations were so accurate that nearly all of his observations are still valid today (Stenuit 1-).


After Aristotle, many scientists have been charmed by dolphins' amazing physical ability, human-like intelligence, and complex social behavior. Recent researches have revealed a lot of new facts about dolphin. Carwardine speculates that ¡§some people are inspired by their ability to explore places out of our reach, experience things we will never see¡¨ (15). Dolphins live in the ocean where most of sunlight is scattered or absorbed in several tens of meters (Pinet 14). Thus, sights are useless in the dark ocean. On the other hand, dolphins mostly rely on sound as their method of obtaining information from their surroundings. Ewan Fordyce and Peter Gill, zoologists and writers of the book, Whales, Dolphins, and Porpoises, explain that sound is much effective in terms of long-distance communication because it can travels faster and longer under water than in air (74). Donoghue and Wheeler point out that dolphins see the world using their sense of sound, which humans can not do since we obtain information of the surroundings using mostly vision, sense of light (7). Dolphins' sophisticated sense of sound has caught a great attention of many scientists.


Now, many researchers agree that dolphins can really do talk to each other using sounds - vocalizations and noise sounds made by tail slapping or leaping. They produce high frequency sounds, which are often classified into three types whistles, squeaks, and clicks (Fordyce and Gill 74). Peter Tyack, a scientist at Woods Hole Oceanographic Institution, says that each of dolphin in a herd has its own signature whistle, which is identical to our name in human society (cited in D'Aulaire and D'Aulaire 57). They also mimic other's signature whistle and include more information in the sounds, changing the frequency or length of them (D'Aulaire and D'Aulaire 57-8). Dan Greenburg, the writer of the article ¡§The Dolphin Affair,¡¨ adds Clicks are used for communication of their emotion (45).


Fordyce and Gill claim that dolphins have a special navigation system called echolocation, in which they produce high frequent sound waves and receive the echo bounced by the object. They are able to locate objects in their surroundings within the vast ranges and able to find preys even if they are very small or hiding in sand (76). It is like our radar or sonar system. Donoghue and Wheeler suppose that dolphin can not hide their emotion from each other because they can see through things due to the property of sound waves penetrating objects (1). They also add, ¡§Telepathic communication. . . may be part of a dolphin's daily life¡¨ (1). There are still so much we have to figure out to understand them better, but this mysteriousness of dolphins fascinates people.


It is probably dolphin intelligence that attracts scientists most. But what does it mean by intelligence? According to Longman Dictionary of American English, the definition of intelligence is ¡§(good) ability to learn and understand.¡¨ Well, it is no doubt that dolphins have an impressive learning and imitating ability if you have ever seen dolphins' performance at marine parks. Donoghue and Wheeler say that dolphins have been known to possess very large brains, which are nearly equal to the size of human brain. However, brain size itself does not indicate its intelligence (8). Fordyce and Gill explain the ration of brain size to body size of dolphins, which is considered a measure of intelligence, are very large and complex. This is thought to correspond to their sophisticated hearing and communication (88).


Many scientists consider dolphins are among most intelligent animals on earth since they found their capability of comprehension of sign languages. Louis Herman, a famous psychologist and director of Kewalo Basin Marine Mammal Laboratory of University of Hawaii, says dolphins can understand the word order and syntax (If Dolphins). For example, when Herman gives a command to his dolphin like ¡§person left Frisbee fetch,¡¨ he brings ¡§the Frisbee on the left to the person in the pool,¡¨ or ¡§surfboard person fetch,¡¨ then he pushes a person over to the surfboard. Herman also claims the grammatical comprehension of the dolphins is equivalent (or superior) to some chimpanzees, also known to show grammatical comprehension (cited in Linden 58). In the next several decades, we might be able to communicate with dolphins using sign languages. We might even be able to develop common language in the form of vocalization like the ones we speak today. But Donoghue and Wheeler say that we are likely to measure their intelligence on our terms, which is just a limitation of our own mind (). The key to the interspecies communication is to break though our own limitation. If we can do it, dolphins must be the ones who lead us to that stage.


Although recent science and technology have disclosed a lot of new facts about dolphins, Carwardine states that ¡§there is something special and particularly appealing about cetaceans. This is difficult to put into words, and impossible to prove, yet it is a feeling shared by a great many people¡¨ (14). The charms of dolphins that have kept us for thousands of years are their gentleness, friendliness and human-like intelligence. And they reflect our longing or respect for the creatures living in the ocean realm ? the unknown world that we never know. These feelings in our heart have stayed unchanged since the ancient era when Greeks and Romans viewed them as our friends in the sea.


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Friday, July 24, 2020

STRUCTURE AND BONDING

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STRUCTURE AND BONDING


In my essay on the structure and bonding in different substances, I am going to focus on electronic arrangement and their effects on the properties of the substance.


METALIC BONDING


Metallic bonding occurs between atoms with low electronegativity (.i.e. 1, or valence electrons); therefore there are many vacancies in valence shell. The crystal lattice of metals consists of ions NOT atoms. When electron clouds overlap, electrons can move into electron cloud of adjoining atoms. The outer electrons (-) from the original metal atoms are free to move around between the positive metal ions formed (+).


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The metal is held together by the strong forces of attraction between the positive nuclei and the ¡¥delocalised' electrons. This is sometimes described as an array of positive ions in a sea of electrons. There is a strong electrostatic force of attraction that two neighbouring nuclei have for the shared electrons between them. - This is the metallic bond. Each atom becomes surrounded by a number of others in a -D lattice, where valence electrons move freely from one valence shell to another. Each positive centre in the diagram represents all the rest of the atom apart from the outer electron, but that electron hasnt been lost - it may no longer have an attachment to a particular atom, but its still there in the structure. Sodium metal is therefore written as Na - not Na+.


The physical properties of metals


This strong bonding and the fact that the particles present in metals are tightly packed in the lattice results in dense, strong materials with high melting and boiling points. The strength, elasticity and ability to bend without breaking of many metals make them useful in construction.


Metals are good conductors of electricity because these free or delocalised electrons carry the charge of an electric current when a potential difference (voltage) is applied across a piece of metal. Copper, for example, is used to make the wire which goes inside electrical cables. Copper is chosen because it can be drawn into long thin wires very easily (it is ductile) and because it is a good conductor of electricity. Metals are also good conductors of heat. This is also due to the free moving electrons. Non-metallic solids conduct heat energy by ¡¥hotter' more strongly vibrating atoms, knocking against ¡¥cooler' less strongly vibrating atoms to pass the particle kinetic energy on. In metals, as well as this effect, the hot high kinetic energy electrons move around freely to transfer the particle kinetic energy more efficiently to cooler atoms. Metals have high melting and boiling points. Strong forces of attraction exist between particles. A large amount of thermal energy is required to overcome the strong electrical forces between the positive ions and the delocalised electrons. These forces operate throughout the lattice.


Metals are lustrous or have a ¡¥silvery surface' but this may be easily tarnished by corrosive oxidation in air and water. The presence of free electrons causes most metals to reflect light. Metals are malleable and ductile. The distortion does not disrupt the metallic bonding. Aluminium is very strong and can be beaten into very thin sheets. It is therefore used in aircraft manufacture.


A metal alloy is a mixture of two or more metals. Adding another element disturbs the pattern in the lattice so that the layers will not slide past each other so easily. Alloys are usually less malleable and ductile than pure metals and they tend to have lower melting points. They do, however, have other properties which make them more useful than pure metals. Some alloys that we use everyday include steel (used for a wide range of things, including knives and forks, building materials and in cars and ships. The coins that we use are all made of copper alloys.


Heat treatment By means of heating and cooling process the strength and hardness of the metal can be changed.


IONIC (ELECTROVALENT) BONDING


Metal atoms are large and hold outer electrons weakly, but non-metal atoms are small and hold outer electrons strongly. This means that when metal and non-metal atoms meet, electrons are lost by the metal atom and gained by the non-metal atom. The non-metal atom gains new outer electrons making a negative ion. Electrons are gained from the metal atom until the outer shell is full. The ions formed have full outer shells. They have the same electronic structure as a noble gas. The oppositely charged ions attract each other and an ionic bond is formed.


Ionic bond the electrostatic force of attraction between two oppositely charged ions formed as the result of electron transfer. Ionic bonds are sometimes called electrovalent bonds.


The physical properties of ionic compounds


All ionic substances have high melting and boiling points. A large amount of thermal energy is required to separate the ions which are bound by strong electrical forces.


Brittleness is again typical of ionic substances. Imagine what happens to the crystal if a stress is applied which shifts the ion layers slightly. Ions of the same charge are brought side-by-side and so the crystal repels itself to pieces.


Many ionic solids are soluble in water - although not all. It depends on whether there are big enough attractions between the water molecules and the ions to overcome the attractions between the ions themselves. Positive ions are attracted to the lone pairs on water molecules and co-ordinate (dative covalent) bonds may form. Water molecules form hydrogen bonds with negative ions. Ionic solids are insoluble in organic solvents. The attractions between the solvent molecules and the ions arent big enough to overcome the attractions holding the crystal together.


Ionic compounds do not conduct electricity, because there are no electrons which are free to move. Molten or aqueous form undergoes electrolysis, which involves conduction of electricity because of the movement of the ions. Once the substance has melted or dissolved, the ions can move and carry charge. Positive ions are attracted towards the cathode they are called cations. Negative ions are attracted towards the anode they are called anions. This is a chemical change rather than a physical process.


The structure of a typical ionic solid - sodium chloride


Compounds like this consist of a giant ionic lattice of ions. There could be billions of sodium ions and chloride ions packed together, or trillions, or whatever - it simply depends how big the crystal is. That is different from, say, a water molecule which always contains exactly hydrogen atoms and one oxygen atom - never more and never less.


A small representative bit of a sodium chloride lattice looks like this the sodium ions and chloride ions alternate with each other in each of the three dimensions.


Only those ions joined by lines are actually touching each other. The sodium ion in the centre is being touched by 6 chloride ions. Sodium chloride is described as being 66-co-ordinated. The pattern repeats in this way over countless ions.


CO-VALENT Molecular BONDING


Covalent bond the electrostatic bonds between the shared pairs of electrons and the neighbouring nucleus.(+) „Æ(-) „Æ(+)


Cl Cl


As well as achieving noble gas structures by transferring electrons from one atom to another as in ionic bonding, it is also possible for atoms to reach these stable structures by sharing electrons to give covalent bonds.


For example, two chlorine atoms could both achieve stable structures by sharing their single unpaired electron as in the diagram.


The two chlorine atoms are said to be joined by a covalent bond. The reason that the two chlorine atoms stick together is that the shared pair of electrons is attracted to the nucleus of both chlorine atoms.


Hydrogen atoms only need two electrons in their outer level to reach the noble gas structure of helium. Once again, the covalent bond holds the two atoms together because the pair of electrons is attracted to both nuclei.


A double covalent bond is where two pairs of electrons are shared between the atoms rather than just one pair as above.


Two oxygen atoms can both achieve stable structures by sharing two pairs of electrons as in the diagram.


The double bond is shown conventionally by two lines joining the atoms. Each line represents one pair of shared electrons.


Ethane CH4 has a double bond between the two carbon atoms.


Co-ordinate (dative covalent) bonding


A covalent bond is formed by two atoms sharing a pair of electrons. The atoms are held together because the electron pair is attracted by both of the nuclei. In the formation of a simple covalent bond, each atom supplies one electron to the bond - but that doesnt have to be the case.


A co-ordinate bond (also called a dative covalent bond) is a covalent bond in which both electrons come from the same atom.


In simple diagrams, a co-ordinate bond is shown by an arrow. The arrow points from the atom donating the lone pair to the atom accepting it.


The weak bonding and the fact that the particles present in covalent molecular substance are loosely packed in the lattice results in low density, weak and soft materials. Weak forces of attraction that exist between particles require very little amount of thermal energy to be broken and so have low melting and boiling points


Covalent molecular substances are bad conductors of electricity and heat because there no mobile charged particles. Molecules are not charged and electrons tightly bound to atoms or shared by atoms in covalent bonds.


Electro negativity


Electro negativity is a measure of the tendency of an atom to attract a bonding pair of electrons.


Consider a bond between two atoms, A and B.


If the atoms are equally electronegative, both have the same tendency to attract the bonding pair of electrons, and so it will be found on average half way between the two atoms. To get a bond like this, A and B would usually have to be the same atom. (For example, H or Cl molecules.)This sort of bond could be thought of as being a pure covalent bond - where the electrons are shared evenly between the two atoms.


If B is slightly more electronegative than A, B will attract the electron pair rather more than A does. That means that the B end of the bond has more than its fair share of electron density and so becomes slightly negative. At the same time, the A end (rather short of electrons) becomes slightly positive.


This is described as a polar bond. A polar bond is a covalent bond in which there is a separation of charge between one end and the other - in other words in which one end is slightly positive and the other slightly negative. Examples include most covalent bonds. The hydrogen-chlorine bond in HCl or the hydrogen-oxygen bonds in water are typical. They are soluble in polar solvents. H or Cl described as a non - polar bond is no separation of charge and the electrons are physically in the centre. They are soluble in non polar solvents.


If B is a lot more electronegative than A, the electron pair is dragged right over to Bs end of the bond. To all intents and purposes, A has lost control of its electron, and B has complete control over both electrons. Ions have been formed (see ionic bonding).


There are patterns of electronegativity in the Periodic Table. The most electronegative element is fluorine. If you remember that fact, everything becomes easy, because electronegativity must always increase towards fluorine in the Periodic Table.


The shape of a molecule or ion is governed by the arrangement of the electron pairs around the central atom. All we need to do is to work out how many electron pairs there are at the bonding level, and then arrange them to produce the minimum amount of repulsion between them.


Two electron pairs around the central atom


The only simple case of this is beryllium chloride, BeCl. It is forming bonds so there are no lone pairs. The two bonding pairs arrange themselves at 180¢X to each other, because thats as far apart as they can get. The molecule is described as being linear.


Three electron pairs around the central atom


The simple cases of this would be BF or BCl.Because it is forming bonds there can be no lone pairs. The pairs arrange themselves as far apart as possible. They all lie in one plane at 10¢X to each other. The arrangement is called trigonal planar.


In the diagram, the other electrons on the fluorine have been left out because they are irrelevant.


Four electron pairs around the central atom


There are lots of examples of this. The simplest is methane, CH4. Four electron pairs arrange themselves in space in what is called a tetrahedral arrangement. A tetrahedron is a regular triangularly-based pyramid. The carbon atom would be at the centre and the hydrogen at the four corners. All the bond angles are 10.5¢X.


GIANT COVALENT Network Substance are substances like diamond, graphite and silicon dioxide.


The physical properties of giant covalent substances They have a very high melting point. Very strong carbon-carbon covalent bonds have to be broken throughout the structure before melting occurs. They very strong and hard. This is again due to the need to break very strong covalent bonds operating in -dimensions. Covalent network substances are brittle. If sufficient force is applied to a crystal, covalent bonds are broken as the lattice is distorted. Shattering occurs rather than deformation of a shape.


They do not conduct heat and electricity (except graphite ¡V see below). All the electrons are held tightly between the atoms, and arent free to move. They are insoluble in water and organic solvents. There are no possible attractions which could occur between solvent molecules and carbon atoms which could outweigh the attractions between the covalently bound carbon atoms.


The giant covalent structure of Diamond


Carbon has an electronic arrangement of , 4. In diamond, each carbon shares electrons with four other carbon atoms - forming four single bonds.


This is a giant covalent structure - it continues on and on in three dimensions. It is not a molecule, because the number of atoms joined up in a real diamond is completely variable - depending on the size of the crystal.


The structure of Graphite


Graphite has a layer structure. The diagram below shows the arrangement of the atoms in each layer, and the way the layers are spaced.


Carbon atom uses three of its electrons to form simple bonds to its three close neighbours. That leaves a fourth electron in the bonding level. These spare electrons in each carbon atom become delocalised over the whole of the sheet of atoms in one layer. They are no longer associated directly with any particular atom or pair of atoms, but are free to wander throughout the whole sheet.


The delocalised electrons are free to move anywhere within the sheet - each electron is no longer fixed to a particular carbon atom. This allows it to conduct electricity. The delocalised electrons are free to move throughout the sheets. If a piece of graphite is connected into a circuit, electrons can fall off one end of the sheet and be replaced with new ones at the other end.


Graphite has a soft, slippery feel, and is used in pencils and as a dry lubricant for things like locks. When you use a pencil, sheets are rubbed off and stick to the paper. It has a lower density than diamond. This is because of the relatively large amount of space that is wasted between the sheets.


The structure of silicon dioxide, SiO


Silicon dioxide is also known as Silicon (IV) Oxide. Crystalline silicon has the same structure as diamond. To turn it into silicon dioxide, we need to modify the silicon structure by including some oxygen atoms. Each Silicon atom is bridged to its neighbours by an oxygen atom.


In conclusion, the electronic arrangement in atom and its interaction with other electrons of the compound (substance) can affect everything, ranging from its reactivity to its structure.


Introduction to Atomic Structure


All substances are made up of molecules made up of atoms. All atoms are made up of ¡¥sub atomic' articles. The structure or all atoms follows a simple predictable structure. All atoms have a very dense central part called the nucleus. Orbiting around this nucleus at a relatively large distance are electrons.


NAMEELECTRIC CHARGEMASSLOCATION


Protons+11Nucleus


Neutrons01Nucleus


Electrons-10 (1/1800) (negligible)Orbiting the Nucleus


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