Chemistry revision notes Essay Example for Free

Chemistry revision notes Essay The oxidation state or oxidation number, is a value assigned to a chemical species which represents its actual or nominal electrical charge. The oxidation number in a free or uncombined element is zero. This means that, metallic magnesium has an oxidation number of zero, and chlorine in Cl2 form has an oxidation state of zero. For simple ionic compounds, the oxidation state of the single atom ions is simply the charge on the ions. In most compounds the oxidation number for hydrogen is +1 and for oxygen is -2. The exceptions include the hydrides (the oxidation state is -1) and the peroxides (the oxidation state for oxygen is -1). In the compounds, halides usually have the oxidation number -1. The sum of all the oxidation numbers in a compound have to be equal to zero. The sum of all the oxidation states in a complex ion is the same as the charge on the ion. Semiconductors A covalent element such as silicon or germanium which has a higher conductivity than that of a typical non-metal but a much lower conductivity than that of a metal is described as a semiconductor. Semiconductors are also referred to as metalloids and they occur at the division between metals and non-metals in the Periodic Table. Key facts : 1. The electrical conductivity of semiconductors increases with increasing temperature. 2: Doping pure crystals of silicon or germanium with certain other elements produces 2 types of semiconductors: n- type and p-type semiconductors. The addition of small quantities of certain substances to pure silicon greatly enhance its conductivity and makes possible the construction of electronic devices. This controlled addition of impurities is called ‘doping’. 1. doping pure silicon with phosphorus or arsenic (group 5 elements) these elements have 5 valence electrons, a few of the silicon atoms are replaced by P, As atoms — 1 electron is left over after the 4 bonds have been formed. The extra electron is free to conduct an electric current and the phosphorus-doped silicon becomes a conductor called n-type. B. doping with boron or aluminium (group 3 elements). By doping with an element having 3 valence electrons some of the silicon atoms are replaced by boron atoms, but because each boron has only 3 electrons, one of the four bonds to each boron atom has only 1 electron in it. We can think of this as a vacancy or hole in the bonding orbital. An electron from a neighbouring atom can move in to occupy this vacancy. As a result of this movement this type of conductor is called p-type. Superconductors 1. Superconductors are a special class of materials that have zero electrical resistance at temperatures near absolute zero. 2. Achieving temperatures near absolute zero is difficult and costly so application of superconduction at these temperatures is impractical. 3. Recently superconductors have been discovered which have zero resistance up to temperatures above the boiling point of liquid nitrogen- temperatures which are less costly to attain. 4. Superconductors may have a future applications in power transmission and electrically powered forms of transport. Chemistry revision notes. (2017, Aug 10).

Preventing STI on Juveniles Essay Example | Topics and Well Written Essays - 1000 words

Preventing STI on Juveniles - Essay Example The effects associated with the acquisition of STIs are not only limited to medical and psychological aspects but have other devastating implications on the infected teenagers including the cost and sequelae of STIs. In order to prevent the spread of sexually transmitted diseases, a diverse range of barrier methods are available, such as condoms to ensure safety of both partners during coitus. In modern society, one of the major problems faced by the health care system is the prevention of sexually transmitted infections in juveniles (Steele et al 2005). Preventive Measures: Abstinence from sexual relations is one of the most efficacious means of reducing the risk of acquiring AIDS and other sexually transmitted infections. On the other hand, maintaining a mutual monogamous sexual relationship with an uninfected partner is another way of minimizing the risk of acquiring STIs through sexual contact. The risk of infection with HIV and other STIs can also be significantly reduced by usi ng barrier methods such as latex condoms or by using spermicides. In heterosexual partners, the prevalence of HIV infection is quite high. In accordance with a recent research, the percentage of heterosexual partners having HIV infection is as high as 11% and about 60% of HIV infected heterosexual partners’ exhibit seropositive results (McGlynn et al 2000). The need for Diverse Interventions: In order to reduce the initial acquisition, further transmission and sequelae of sexually transmitted infections, there is an urgent need to formulate and strictly implement a diverse range of interventions. Interventions such as fostering the use of condoms, development of new biomedical methods, school-college based educational programs and routine screening have simply not been able to cause a sharp decrease in the incidence of sexually transmitted infections in sexually active young individuals. It is a fact that these interventions have significantly increased the awareness about ST Is but the rapid increase in the number of cases reported each year mirrors their inefficacy. The alarming rise in the number of teenagers having STIs reflects the failure of the government in the implementation of effective and diverse interventions at every level. Therefore, the need for drawing up and strictly enforcing effective projects for the prevention of STIs is the greatest now than ever before (Steele et al 2005). Design for Change in Practice: To ensure effective outcomes, it is a prerequisite for the interventions mentioned in this section to be implemented comprehensively and at different societal levels. The new design for change in practice will address the following areas of concern. The most effective way of sharply decreasing the percentage of new STI cases is to convey the importance of sexual abstinence to young individuals. The advent of new biomedical approaches, such as vaccines, has been assumed to provide easy and instant solution to the critical problem of rise in STIs in juveniles. However, it is quite unrealistic to believe that such approaches will provide fast and instant solution. The realistic approach is to couple these biomedical approaches with behavioral approaches in order to increase their effectiveness and efficacy. Thirdly, it is quite important to realize that teenagers need to be informed about how to properly use condoms during sexual intercourse. Unfortunately, a large number of community or school based programs and parent

Strengths and weaknesses of Rolls Royce Essay Example | Topics and Well Written Essays - 1750 words

Strengths and weaknesses of Rolls Royce - Essay Example This research will begin with the statement that Rolls Royce has been a pioneer in the motor car market for over 100 years. It continues to set the standard for motor cars in the industry. Financial ratios help to analyze the financial health of a company. Gross profit margin is an indicator of how %age of a sales dollar is left after the payment of the goods has been made. It is the actual markup on the goods sold. It is better for the company if it has a higher gross profit margin. Rolls Royce gross profit margin has been stable for the past 5 years. There hasn’t been much change in the gross profit margin of the company. This means that with respect to each unit of the product the margin has been consistent and hence the company has been effectively maintaining the process of manufacturing of goods. Operating profit margin indicates the profit margin after payment is made for goods as well as its fixed expenses and other variables. This again has been stable for Rolls Royce with no sharp changes. This means that company understands its business very well and is very effective in managing it. The company has knows how to efficiently manage the various processes of its business. Net Profit margin is the actual measure of a company’s financial success. Net profit margin indicates how profitable the company is. Therefore, higher the net profit margin more profitable the company is. Rolls Royce’s performance with respect to net profit margin has been very inconsistent over the past 5 years.