Steric Number Definition in Chemistry

The steric number is the number of atoms bonded to a central atom of a molecule plus the number of lone pairs attached to the central atom. The steric number of a molecule is used in VSEPRÂ  (valence shell electron pair repulsion) theory to determine the molecular geometry of a molecule. How to Find the Steric Number To determine the steric number, you use the Lewis structure. The steric number gives the electron-pair arrangement for the geometry that maximizes the distance between valence electron pairs. When the distance between valence electrons is maximized, the energy of the molecule is at its lowest state and the molecule is in its most stable configuration. The steric number is calculated using the following formula: Steric Number (number of lone electron pairs on the central atom) (number of atoms bonded to the central atom) Heres a handy table that gives the bond angle that maximizes separation between electrons and gives the associated hybrid orbital. Its a good idea to learn the bond angle and orbitals since these appear on many standardized exams. S# bond angle hybrid orbital 4 109.5Â ° sp3 hybrid orbital (4 total orbitals) 3 120Â ° sp2 hybrid orbitals (3 total orbitals) 2 180Â ° sp hybrid orbitals (2 total orbitals) 1 no angle s orbital (hydrogen has an S# of 1) Steric Number and Hybrid Orbital Steric Number Calculation Examples Methane (CH4) - Methane consists of carbon bonded to 4 hydrogen atoms and 0 lone pairs. Steric number 4.Water (H2O) - Water has two hydrogen atoms bonded to oxygen and also 2 lone pairs, so its steric number is 4.Ammonia (NH3) - Ammonia also has a steric number of 4 because it has 3 hydrogen atoms bonded to nitrogen and 1 lone electron pair.Ethylene (C2H4) - Ethylene has 3 bonded atoms and no lone pairs. Note the carbon double bond. Steric number 3.Acetylene (C2H2) - The carbons are bonded by a triple bond. There are 2 bonded atoms and no lone pairs. Steric number 2.Carbon Dioxide (CO2) - Carbon dioxide is an example of a compound that contains 2 sets of double bonds. There are 2 oxygen atoms bonded to carbon, with no lone pairs, so the steric number is 2. Shape Versus Steric Number Another way to look at molecular geometry is to assign the shape of the molecule according to steric number: SN 2 is linear SN 3 is trigonal planar SN 4 is tetrahedral SN 5 is trigonal bipyramidal SN 6 is octahedral Key Takeaways for Steric Number In chemistry, a molecules steric number is the number of atoms bonded to the central atom plus the number of lone electron pairs surrounding the central atom.The steric number is used in VSEPR theory to predict molecular geometry.

The Effects Of Media Violence On Children - 1943 Words

For many years now, the media has been a big part of our lives. Almost everybody in the world is or has connected to it one way or another. It is a way for families and friends to have fun together, for interesting topics that people are interested in, or to just enjoy alone. However, there is a problem that can be seen across all types of media: violence. Violence can be seen as a distraught way to get over problems. There is judgement issues involved for violence. It is done by bullies in school, adults at a bar, gangs on the streets, but there is no greater effect on children, pertaining to violence, than the media. It is very destructive and could harm the youth in a mental way. Children are exposed to massive amounts of depictions of violence in many forms of media, and have become desensitized and more aggressive; therefore an effort should be made to teach children about empathy. Media can be traced back to ancient times with literature, but more advanced types of media emerg ed within the nineteenth and twentieth century. This includes the invention of movies and television. Going more along the timeline, the invention and rising popularity of video games in the 1970s and 1980s is seen as well. Violence has been included in all of these media forms, whether it be mild or severe. â€Å"For more than five decades, Americans have been concerned about the frequent depiction of violence in the mass media and the harm these portrayals might do to the youth† (AndersonShow MoreRelatedThe Effects Of Media Violence On Children873 Words   |  4 Pages According to the Media Education Foundation, once a child reaches eighteen years of age, they have witnessed around 200,000 acts of violence and 16,000 murders (jacksonkatz.com). Our society loves entertainment and a grand portion of this entertainment contains violence. Children constantly consume violent visuals, due to their prevalence. Majority of our society is uninterested in the effects of media viol ence since its effects do not show immediately. Misinformation is our greatest enemy in theRead MoreThe Effects Of Media Violence On Children974 Words   |  4 Pagesmany kinds of media, like Internet, video game, television and film. It is generally believed that some of the bad information such as violent content in the media can have a negative effect on people, and it can end up causing some social problem. It is clear that children are more likely to be influenced by media violence than other age groups because of their world outlook and personality are not formed. Furthermore is if media violence does have some profound influence on children, this will leadRead MoreThe Effects Of Media Violence On Children884 Words   |  4 Pagesis all this necessary to fabricate in the media? What are characters in movies teaching kids? What about the language in music talking about killing people and talking about violence like it’s the cool thing? What about new channels always ta lking about guns, bombs and threats to the public, is this what is influencing are children because they view it as a norm? Some may agree with this as others may disagree. Media violence is not the factor in violence today. Studies show that over 90% of homesRead MoreThe Effects Of Media Violence On Children1357 Words   |  6 Pagesthe graphic cruelty and violence. According to American Psychological Association, the harmful influence of media violence on children dates back to the 1950s and 1960s, and remains strong today. A child that watches violence or hears about violence can be influenced to become violent. Indeed, in reviewing the totality of empirical evidence regarding the impact of media violence, the conclusion that exposure to violent portrayals poses a risk of harmful effects on children has been reached by theRead MoreThe Effects Of Media Violence On Children2411 Words   |  10 PagesMedia Violence is definitely harmful to children as the exposure of media violence can desensitize children (age 6-12) to violence and in the real world; violence becomes enjoyable and does not result in apprehensiveness in the child. There have been s everal studies and experiments regarding the adverse effects of violence used in video games, television, as well as movies. With both preschool and school-aged children, studies have found that they are more likely to imitate the violence they seeRead MoreThe Effects Of Media Violence On Children2122 Words   |  9 Pagesexposed to various types of media, for example books or magazines, television, song lyrics, video games, and movies. Media often portrays, aggressive action, behaviour, and violence. This content can negatively affect not only adolescents and adults, but can have an even greater effect on children even from the moment they are exposed to it. Children who are exposed to violence in the media may display aggressive and violent behaviour. Young people especially children under the age of eight thisRead MoreThe Effects Of Media Violence On Children1903 Words   |  8 Pagesdepict different forms of violence. Some people feel that there is too much violence exposed in the media. Many studies have made the claim that the media is responsible for much of the violence seen in the world we live in. However, people have choices and responsibilities we cannot allow ourselves to blame it on other things such as the media. The violence seen in our media has an impact on both adults and children. Since children are also exposed to various forms of media, there has been additionalRead MoreEffects of Media Violence on Children2430 Words   |  10 PagesThe Effect of Media Violence on Children and Levels of Aggression. It has been said that children are like sponges when it comes to attaining knowledge. This seems to be true whether they are learning to speak or how to show emotion. Feelings and emotions become more imminent once children begin to go through adolescents. Children acquire the ability to aggression, sadness, and happiness more readily. Males typically exhibit higher levels of aggression then females according to some researchRead MoreThe Effects Of Media Violence On Children1270 Words   |  6 Pagesdifferent forms of violence. Some people feel that there is too much violence exposed in the media. Many studies have made the claim that the media is responsible for much of the violence seen in the world we live in (List and Wolfgang). However, people have choices and responsibilities we cannot allow ourselves to blame it on other things such as the media. The violence seen in our media has an impact on both adults and children. Since children are also exposed to various forms of media, there has beenRead MoreWhat Is the Effect of Media Violence on Children1314 Words   |  6 PagesYasser Abdelaziz Ms. Williams English 1010-18 13, December 2010 The Effect of Media Violence on Children Although very little research was done on it in the past, media violence has sparked much controversy in recent history. As technology becomes more advanced, new methods of uncovering the media’s effects on children have emerged. Advances in Neuroscience, for example, can become tools to understanding the effects media violence has from a psychological standpoint. The brain in its underpinnings

The Interaction Between Heredity and Environment Free Essays

Have you ever wondered why people resemble their parents? The answer to this and other questions about inheritance lies in a specialized branch of biology called genetics. Geneticist found that most aspects of life have a hereditary basis and that many traits can appear in more than one form. For instance, human beings have blond, or red, or brown, or black hair. We will write a custom essay sample on The Interaction Between Heredity and Environment or any similar topic only for you Order Now They may have one of several different types of blood, one or several colors of skin. Their ear lobes may be attached or free. They may or may not be able to manufacture certain enzymes. Some of these traits are much more important to the life of the individual than others, but all of them are hereditary. The geneticist is interested not only in the traits of man but in those of all other organisms as well. The study of inheritance depends on the differences as well as the similarities between parents and offspring over several generations. Heredity is very complex, and a geneticist cannot possibly analyze all the traits of an organism at once. Instead, he studies only a few traits at a time. Many other traits are present. As the geneticists work out the solution to each hereditary mystery, the geneticist must not forget that all organisms live in a complex environment. The environment may affect the degree to which a hereditary trait develops. The geneticist must try to find out which of the many parts of the environment may affect his results. The factors must be kept as constant as possible by using controlled experiments. Only then can he tell that the differences observed are due to heredity. Heredity determines what an organism may become, not what it will become. What an organism becomes depends on both its heredity and environment. The modern science of genetics started with the work of Gregor Mendel. He found that a certain factor in a plant cell determined the traits the plant would have. Thirty years after his discovery this determines was given the name gene. Of the traits Mendel studied, he called dominant those at showed up in the offspring and recessive those The question I will ask is: how much of the variability observed between different individuals is due to hereditary differences between them, and how much to differences in the environments under which the individuals developed? In most organisms, including man, genetics information is transmitted from mother to daughter cells and from one generation to the next by deoxyribonucleic acid (DNA). Knowledge of the heredity or inheritance of plants and animals is important in many phases of our life. The question I will ask is: How much of the variability observed between different individuals is due to hereditary differences between them, and how much to differences in the environments under which the individuals developed? The purpose of designing a unit on ? Heredity And Environment? is to help students learn more about themselves. They will learn why they develop into the kind of individual they are. The unit will discuss heredity traits and environmental conditions, chromosomes, DNA, studies of identical twins, and several diseases linked to heredity and environment. The students will do some hands on activities by constructing a model which represents DNA. They will explore plants with the exact same heredity and plants with different heredity. They will change the conditions in the environment to see the way the plant organisms with the same heredity may develop differently in different environments and why organisms with different heredity develop in the matter in which they do. Heredity is not the only thing that effects development. The environment also has an important effect. The unit can be taught to students in grades five through eight. The science and math teachers are encouraged to use a team teaching approach. Other features that will be included in the unit are content, lesson plans, resources, reading list and a bibliography. Genes and DNA DNA, short for deoxyribonucleic acid, makes up the genes that transmits hereditary traits. The DNA molecule looks like a long, twisted rope ladder. This is called the double helix. The ladder is made up of two coiled strands with rungs between them. The rungs are composed of pairs of chemicals in different combinations. Each combination carries instructions like the dot and dashes of the Morse Code. Each gene in the body is a DNA section with full set of instructions for guiding the formation of just one particular protein. The different proteins made by the genes direct the body? functions throughout a person? s life. DNA is made of six parts: a sugar, a mineral (phosphate), and four special chemicals called bases. These bases are represented as A;T;C; and G. Sugar and phosphate form the chains, or sides, of the staircase. The A;G;C and T bases form the steps. See figure 1. Each step is made of two pieces, which are always paired the same way. The A base always pairs w ith the T base. And the G base always pairs with the C base. Figure 1. DNA Structure (figure available in print form) DNA Reproduces Itself Two new identical DNAs are immediately formed. The A,G,C, and T bases on each chain attract loose bases found floating within the nucleus. Ts attract As and Cs attract Gs. The two new DNAs are just like the original DNA. Each strand directs the synthesis of a complementary strand. The replication of DNA is the key to heredity, the passing of traits from parents to offspring. DNA replication results in the formation of new reproductive cells. It also results in the formation of new cells, which is important for the growth of an organism. See Fig. 2. Figure 2. (figure available in print form) Watson-Crick? DNA Replication-Redrawn from version in Levine, Genetics, Holt, Rinehart, Winston, 1968. Chromosomes Genes and chromosomes provide the genetic link between generations. Chromosomes are strands of DNA and protein found in the nucleus of virtually every cell, but with few exceptions seen only during the process of cell division. The number of chromosomes in a cell is characteristic of the species. Some have very few, whereas others may have more than a hundred. Ordinarily, every cell in the body of an organism contains the same number of chromosomes. The most important exception is found in the case of gametes where half the usual number is found. Human beings have 46 chromosomes in each cell, with the exception of the spermatozoa in males and the ova in females, each of which has 23 chromosomes. Human chromosomes occur in pairs, the total 46 consisting of 23 pairs; 22 pairs of autosomes which are non-sex determining chromosomes. The member of a pair are essentially identical, with the exception of sex chromosomes in males, and each pair is different from any other pair. Plants and animals inherit chromosomes from their parents. Each plant and animal cell has a set of chromosomes. Chromosomes, then, control the heredity of an organism. They carry the blueprint that determines what kind of organism will develop. Some Relationship Between Heredity And Environment Organisms can transmit some hereditary conditions to their offspring even if the parents do not show the trait. In the small, familiar fruit fly. Drosophila, there is a hereditary trait in which the wings curl up sharply if the files are raised at a temperature of 25 degrees Celsius. If, however, the files are raised at a lower temperature, such as 16 degrees Celsius then the trait rarely appears. The wings seem to be straight, and the flies look normal. The genetic trait is there, however, and will reappear in the next generation if the temperature returns to 25 degrees Celsius. See fig. 3. A similar type of inheritance appears in plants. In some types of corn the kernels will remain yellow until they are exposed to sunlight. Once exposed, the kernels become various shades of red and purple. Some traits do not appear to be affected by the environment. One of the first hereditary traits studied in humans was polydactyly. An individual with polydactyly has more than ten figures or toes. See fig. 4. This trait does not seem to be affected by the environment at all. Other human traits like color blindness, baldness, blood type, skin color, the ability to taste certain substances, the presence or absence of hairs on the middle of the fingers, and free or attached ear lobes do not seem to be influenced by the environment. (figure available in print form) Figure 3? This diagram shows how temperature affects curly-wing trait in Drosophila. If the third generation of curly-winged flies had been raised in 16? C environment. Source:Redrawn from Biological Science, Houghton, Mifflin Co. , Boston, 1963, p. 379. Figure 4? An example of polydactyly. Extra digits on either hands or feet are almost always abnormal in structure. (figure available in print form) Source: Biological Science, Houghton Mifflin Co. , Boston, 1963. p. 380. A common cited example of an environmental effect on phenotype is the coloring of Siamese Cats, although these cats have a genotype for dark fur, the enzymes that produce the dark coloring function best at temperatures below the normal body temperature of the cat. Siamese Cats are noted for the dark markings on their ears, nose, paws, tail, and all areas that have a low body temperature. If the hair on the cat? s belly is shaved and an ice pack is applied, the replacement hair will be dark. Likewise, a shaved tail, kept at higher than normal temperatures, would soon be covered with light colored fur. These changes are temporary, however, unless the ice pack or heat source is maintained permanently. The most celebrated effect of an environmental agent directly affecting the unborn, is that produced by the rubella virus. This German measles virus is capable of crossing the placenta from mother to child, and the prenatal infection, if it occurs early enough, may result in deafness and other damage to the child. Similarly, maternal infection with the rare protozoan parasite Toxoplasma can cause serious congenital defects in the fetus, and the same has been suspected for Asian influenza. Another environmental factor is anoxia. Anoxia is a natural hazard of childbirth, and in most cases the infant makes a normal adjustment to it. When infants suffer from delayed respiration or asphyxia during birth, it is widely accepted that this is responsible for later difficulties such neurologic abnormalities. Warburton and Fraser have emphasized that the development of a fetus depends on a precise and extremely intricate system of interactions between two sets of hereditary factors and two environments, all acting at the same time on the growing baby. The mother and the fetus each have their own environment and their own genotype. How to cite The Interaction Between Heredity and Environment, Essay examples