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The numbers in Maori
QuizĀ by Malcolm Roberts
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Select all the numbers that can be used as a common denominator to rewrite the fractions __ 2 6 and __ 1 2 . A 3 D 12 B 6 E 16 C 8 2 Aaron ran __ 5 8 mile to his friendās house. Then he ran another __ 1 4 mile to the park. 1 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 4 Which equation shows how many miles Aaron ran? A __ 5 8 ā __ 1 4 = __ 2 8 C __ 5 8 + __ 1 4 = __ 7 8 B __ 5 8 ā __ 1 4 = __ 3 8 D __ 5 8 + __ 1 4 = __ 8 8 3 Select all the expressions that can be used to find the sum of __ 6 8 and ___9 12. A ___ 36 48 + ___ 36 48 D ___ 18 20 + ___ 17 20 B ___ 24 36 + ___ 27 36 E ___ 18 24 + ___ 18 24 C ___ 14 16 + ___ 13 16 4 Write a pair of equivalent fractions for __ 3 4 and __ 2 5 using a common denominator of 20. __ 3 4 = __ 2 5 = 5 Katie spent __ 4 5 hour painting and __ 1 2 hour drawing. ? 1 1 2 1 5 1 5 1 5 1 5 How much more time in hours did she spend painting than drawing? 6 Dave is planting a garden. He plants cucumbers in ___2 12 of his garden and tomatoes in __ 2 3 of his garden. What fraction of his garden does Dave plant with cucumbers and tomatoes? 7 Of the students in Mariaās class, __ 2 5 have dogs and __ 1 3 have cats. No students have both a dog and a cat. What fraction represents how many more students in Mariaās class have dogs? 52 Ā© Houghton Mifflin Harcourt Publishing Company Module 6 ⢠Form A Name Module Test DO NOT EDIT--Changes must be made through "File info" CorrectionKey=NL-C 9 Mr. Gonzales used __ 3 4 quart of broth and __ 1 2 quart of milk to make soup. How many quarts of liquid did he use? Part A Complete the fraction model to represent the problem. 1 1 2 1 4 1 4 1 4 Part B Write an equation to show how many quarts of liquid Mr. Gonzales used to make soup. 10 A bowl of cereal contains __ 2 3 cup of oats and __ 2 8 cup of raisins. Write a numerical expression using equivalent fractions with a common denominator of 24 to model how many more cups of oats than raisins there are in the bowl. 11 Jessica read __ 1 6 of her book on Thursday, __ 2 9 of her book on Friday, and __ 1 2 of her book on Saturday. Part A Write a numerical expression using equivalent fractions to model how much of her book she has read so far. Part B What fraction of her book has Jessica read?
Create MCQs from this text "For as long as we can remember, innovation has been a top priorityāand a top frustrationāfor leaders. In a recent McKinsey poll, 84% of global executives reported that innovation was extremely important to their growth strategies, but a staggering 94% were dissatisfied with their organizationsā innovation performance. Most people would agree that the vast majority of innovations fall far short of ambitions. On paper, this makes no sense. Never have businesses known more about their customers. Thanks to the big data revolution, companies now can collect an enormous variety and volume of customer information, at unprecedented speed, and perform sophisticated analyses of it. Many firms have established structured, disciplined innovation processes and brought in highly skilled talent to run them. Most firms carefully calculate and mitigate innovationsā risks. From the outside, it looks as if companies have mastered a precise, scientific process. But for most of them, innovation is still painfully hit-or-miss. What has gone so wrong? The fundamental problem is, most of the masses of customer data companies create is structured to show correlations: This customer looks like that one, or 68% of customers say they prefer version A to version B. While itās exciting to find patterns in the numbers, they donāt mean that one thing actually caused another. And though itās no surprise that correlation isnāt causality, we suspect that most managers have grown comfortable basing decisions on correlations. Why is this misguided? Consider the case of one of this articleās coauthors, Clayton Christensen. Heās 64 years old. Heās six feet eight inches tall. His shoe size is 16. He and his wife have sent all their children off to college. He drives a Honda minivan to work. He has a lot of characteristics, but none of them has caused him to go out and buy the New York Times. His reasons for buying the paper are much more specific. He might buy it because he needs something to read on a plane or because heās a basketball fan and itās March Madness time. Marketers who collect demographic or psychographic information about himāand look for correlations with other buyer segmentsāare not going to capture those reasons. After decades of watching great companies fail, weāve come to the conclusion that the focus on correlationāand on knowing more and more about customersāis taking firms in the wrong direction. What they really need to home in on is the progress that the customer is trying to make in a given circumstanceāwhat the customer hopes to accomplish. This is what weāve come to call the job to be done. We all have many jobs to be done in our lives. Some are little (pass the time while waiting in line); some are big (find a more fulfilling career). Some surface unpredictably (dress for an out-of-town business meeting after the airline lost my suitcase); some regularly (pack a healthful lunch for my daughter to take to school). When we buy a product, we essentially āhireā it to help us do a job. If it does the job well, the next time weāre confronted with the same job, we tend to hire that product again. And if it does a crummy job, we āfireā it and look for an alternative. (Weāre using the word āproductā here as shorthand for any solution that companies can sell; of course, the full set of ācandidatesā we consider hiring can often go well beyond just offerings from companies.)"
Got a presentation to make? Easy enough. Think of this as an opportunity to convince someone to see your point of view. One effective way to do that is by using data. Data is facts, numbers, and figures used to report the results of the research. Using data can be helpful to explain complex subjects. Here's how to do it. Research your topic to find data to support your presentation. Step 2. Be sure that any facts or figures you use are from reliable sources, like government, university, and scientific websites or trusted news outlets. You have to be careful. There is a lot of fake information floating around. Step 3. Take the time to edit your data so you're only using what's important and relevant to your topic. Reciting a long list of facts and numbers can put your audience to sleep. Step 4. Remember your data has to tell a story. Choose the right words and phrases to describe your findings. Reports indicate a sharp decrease in costs. Step 5. Take your facts and numbers and turn them into something exciting. This chart shows we had a boom in exports. Almost any data can be used to create colorful and eye-catching graphics and charts. In this graph, you can see a dramatic increase. Which makes it more memorable and 100% more entertaining to watch. Thank you.
Legislative Structure: Congress -- two houses: Senate (2 senators from each state, 6 year terms, must be at least 30 years old and have been a citizen for at least nine years) -- Constitution originally allowed state legislatures to choose the two senators but now elected by popular vote House of Representatives (number based on population of state, determined every ten years in a census -- number now set at 435; 2 year terms, must be at least 25 years old and have been a citizen for 7 years) Legislative Powers: Makes the laws -- any senator or representative can propose a bill -- if majority in one house favors it, bill goes to other house for debate -- if approved by both -- goes to the president to be signed into law -- President can veto any proposed law but can then be overruled if there is a two thirds majority in both houses favoring the law Elastic Clause -- can make all laws ānecessary and properā to carry out its other powers Only the House of Representatives can propose new taxes Only Congress can decide on how to spend the money raised through taxes Power to raise (pay for) an army and navy To declare war Approves treaties and executive appointments -- Senate How was the debate over how the president should be chosen resolved? The Electoral College System -- made up of electors who cast votes to elect the president and vice-president every four years Each state has as many electors in the Electoral College as the number of senators and reps it sends to Congress. The votes cast by electors are called electoral votes. Delegates left the method of choosing electors up to each state. Before 1820, state legislatures chose electors in most states. Today, people choose their stateās electors when they vote in presidential elections. The electors then cast their ballots for president and vice-president on a date chosen by Congress. Today must win at least 270 of the 538 total electoral votes
⢠There are two groups of animals which are important in agriculture. ⢠The groups are domestic and wild animals. 1. Domestic animals ⢠These are animals which are trained to live with people in their homes. ⢠Some examples includes : Uses of domestic animals ⢠Source of food, for example milk, eggs and meat. ⢠For cultural purposes, for example paying lobola. ⢠Some are used for transport and labour. ⢠Domestic animals can also be a source of income. 2 . Wild animals ⢠These are animals which are found in game reserves and in the forests ⢠They are also called game animals. ⢠Examples of wild animals are: Uses of wild animals ⢠Some of the wild animals give us meat, hides and ivory. ⢠Wild animals attract visitors from other countries, so the country gets money. Wednesday 06 September 2023 Exercise: Domestic animals 1. What is a domestic animal? [2] 2. What is a wild animal? [2] 3. Name any 4 domestic animals that you know. [4] 4. State any 2 uses of domestic animals. [2] 5. Name any 3 wild animals that you know. [3] 6. Give 2 uses of wild ani mals. [2] 7. Wild animals can also be called animals. [1] ⢠Animals, like human beings need good food to help them to grow and reproduce. ⢠The main sources of food for animals include stock feeds, pastures, veld grass, crop remains and cereal grains. ⢠These foods contain the most needed essential nutrients. Nutrient Function carbohydrates Gives energy Fats Give energy and warmth Proteins Helps in growth and repair of body parts Minerals Help in the formation of bones and teeth Vitamins Help develop good sight, improve fertility and help animals fight diseases Water Transports food in the body, cools the body and remove waste from the body. ⢠Livestock are domesticated animals that are kept for food, use or for sale. ⢠Small livestock has many uses. ⢠They are a good source of food. ⢠They also give us manure to use in gardens. ⢠We get clothes and medicine as well from small livestock ⢠Examples of small livestock are rabbits, sheep, goats and all form of poultry Poultry ⢠All animals that are kept by farmers which have wings and feathers and lay eggs are called poultry. ⢠They are a good source of white meat, eggs and manure. ⢠They are also a source of income when we well them and their products. ⢠Poultry includes chicken, guinea fowl, ducks, turkey, pigeons and quail birds. Rabbits ⢠Rabbits have 3 known uses which are: ļ¼They are kept for meat ļ¼Kept for pelts. (pelt is animal skin used to make blankets, hats and jackets) ļ¼They are used at agricultural shows ⢠Rabbits are cheap to buy, easy to keep and feed. ⢠They take about 4 months to mature. ⢠Rabbits are fed using green vegetables and rabbit pellets. Wednesday 20 September 2023 Small livestock 1. Give 3 examples of small livestock. [3] 2. State 3 things that are provided by small livestock. [3] 3. What are the 2 uses of rabbits? [2] 4. Pelts are used to make _________________ [1] 5. State any 4 examples poultry. [4] 6. Rabbits take ___________ months to mature. [1] 7. What is poultry? ⢠Apiculture is the keeping of bees in order for them to produce honey for sale. ⢠Apiculture is very important because: (i) Provides honey - a valuable nutritional food (ii) Provides bees wax - which has many uses in industry Uses of wax ļ¼For making candles ļ¼Polish furniture ļ¼Make crayons ļ¼Prevent tools from rusting (iii) Honey bees are excellent pollinating agents, thus increasing agricultural yields. BEE COLONY Inhabitants of the bee colony and their roles ⢠A honey bee colony typically consists of three kinds of adult bees: ļ¼ļ workers, drones and the queen 1. Workers ⢠Workers are the smallest and constitute the majority of bees occupying the colony. ⢠They do not lay eggs. ⢠Workers have specialized structures, such as brood food glands, scent glands, wax glands, and pollen baskets. ⢠these allow them to perform all the labors of the hive. Roles of the worker bees ļ¼they forage for nectar, pollen, water, and plant sap. ļ¼They clean and polish the cells. ļ¼feed the brood. ļ¼care for the queen. ļ¼remove debris. ļ¼handle incoming nectar. ļ¼build beeswax combs. ļ¼guard the entrance. 2. Drones ⢠Drones (male bees) are the largest bees in the colony. ⢠They are generally present only during late spring and summer. ⢠The droneās head is much larger than that of either the queen or worker. ⢠Drones have no stinger, pollen baskets, or wax glands. ⢠Their main function is to mate with the queen. 3 . Queen ⢠Each colony has only one queen. ⢠The queen is the largest of the bees in a bee colony. ⢠The Queen Bee plays a vital role in the hive because she is the only female with fully developed ovaries. ⢠She produces both fertilized and unfertilized eggs. ⢠Queens lay the greatest number of eggs in the spring and early summer. ⢠The queen also produce chemical scents that help regulate the unity of the colony. 1. What is apiculture? [2] 2. Give 3 reasons why apiculture is important in Zimbabwe. [3] 3. Name the 3 inhabitants of the bee colony. [3] 4. Briefly explain the roles of each inhabitant named in number 3. ⢠Apart from using hand tools, farmers also use some farm implements and machinery to carry out their field work. ⢠Machines help farmers do their work more easily and quickly. ⢠The most common implements used by farmers to grow, harvest and transport their produces are: ļ¼ mouldboard plough ļ¼Cultivator ļ¼Scotch cart ļ¼Harrow ļ¼Planter ļ¼Maize sheller ļ¼ combine harvesters ļ¼Boom sprayers Disc harrow Spike toothed harrow KNAPSACK SPRAYER ⢠Farming is a business. ⢠Communal farmers grow crops and keep animal mainly for their own use. ⢠If there is any extra they sell to get money. ⢠Commercial farmers grow crops and keep animals for sale. ⢠Crops and animals produced are called farm produce. ⢠There are places were farmers have to sell their produce. ⢠Farmers can take their produce to local markets. ⢠A market is a place where buying and selling occurs. ⢠Some of the local markets includes: ļ¼A shopping centre ļ¼A school ļ¼A nearest bus stop ļ¼A local village ļ¼A school ļ¼Local Grain Marketing Board depot (GMB) Types of farm produce ļ¼Beef ļ¼Fruits ļ¼Mutton ļ¼Eggs ļ¼Vegetables ļ¼Pork ļ¼Milk ļ¼Chicken ļ¼Cereals/grains ļ¼beans
Industry of Southeast Asia Industrialization in Southeast Asia is a relatively recent phenomenon, much of the development having occurred only since the early 1960s. As mentioned above, industrialization policies have been critical goals in the market economies of the ASEAN countries; and, in all of them except Brunei, industryās share of the GDP has grown considerably. The most significant increases have occurred in Singapore, Thailand, and the Philippines. Manufacturing in particular has accounted for the greatest changes, with Indonesia, Malaysia, and Thailand making especially large gains during the 1980s. Small factories dominate, both in terms of the number of companies and the number of workers employed. Agricultural processing is most important in virtually all nations. The notable exception is Singapore, where the manufacture of a variety of products, headed by electrical and electronic and transport equipment, is dominant. In Thailand, Myanmar, and the Philippines, textiles and clothing are significant, as is the chemical industry in Thailand and Indonesia. Light, labour-intensive goods, such as electrical and electronic products, are increasingly important. It is in the manufacture of these products and textiles that the most employment has been gained. Tin is the most important metallic mineral in the region in terms of value, and Thailand, Malaysia, and Indonesia account for more than half of world production. In Malaysia and elsewhere, however, alluvial lodes are becoming depleted, and the remaining concentrations are less economical to mine. Fluctuating market prices have also discouraged tin production. Nickel, copper, and chromite are also mined, although the quantities produced in the region are minor in terms of world production. Southeast Asia has considerable reserves of oil and natural gas, notably in Indonesia, Malaysia, and Brunei. Trade Given Southeast Asiaās strategic location and the early development of trade there, it is not surprising that trade is especially important to all nations in the region. The value of regional trade is about one-third that of the United States. Most striking is the almost total dominance of trade by the market economies. Exports, as a percentage of the GDP, are small in Cambodia, Myanmar, Vietnam, and Laos and moderately so in Thailand, the Philippines, and Indonesia. Countries with a relatively large proportion of export trade are Singapore, Malaysia, and Brunei. Composition of exports is important. In this respect, Indonesiaāthe trade structure of which long has been dominated by oilāhas been relatively successful in diversifying its exports toward plywood, rattan, coffee, rubber, and textiles. Conversely, Malaysia, with a trade pattern of exporting palm oil, tropical hardwoods, and tin, now derives the majority of its export income from petroleum products. This revenue has been used to build up the countryās industrial base. Thailand exhibits a much less diverse export structure, where food and manufactured goods account for nearly all of its total trade. Likewise, Brunei relies almost entirely on its petroleum exports. Singapore, however, has utilized its unique geographic position and highly educated labour force to attract multinational corporations. As a result, investment in the manufacturing and, increasingly, service sectors has greatly expanded. Intraregional trade among the ASEAN members, while important, accounts for only about one-fifth of Southeast Asiaās total trade. Philippine trade within the region is especially small, reflecting its long-term orientation toward the United States. Far more important, therefore, is the trade with countries outside the region, dominated by that with Japan, Europe, and the United States; increasingly significant, however, is the trade with Taiwan, China (especially Hong Kong), and South Korea.
Make mcq quiz with 4 option in which one is correct -'10 Basis of Material Science ⢠.....;;;";;;"~~;;,,;;,,,,;.;.,,;;,,,;,,;.;,.,------------ 6. Temporary materials: Some materials are meant to be placed in the oral cavity for a short period of time for different reasons. ⢠Temporary crowns: While a permanent crown is prepared in the dental laboratory, the patient must wait for few days before it can be fabricated and cemented into place. Does patient experience any problems during this time period? If the tooth is vital (the pulp is alive), the patient is likely to experience pain and sensitivity while eating and drinking, also it looks unesthetic. What can be done to solve this problem? A temporary crown is placed before the patient leaves the clinic. It is constructed and luted in the same appointment in which the crown preparation is done. Temporary crowns are not very strong or esthetic but they serve adequately till the permanent crown is ready to be cemented. ⢠Temporary restorations: Sometimes it is difficult to decide immediately the best line of treatment for a particular tooth. The exact condition of the pulp may not be obvious to the dentist from the patient's symptoms. A dentist removes all or part of the decay and then places a temporary restoration to have time to observe the behaviour of the pulp or to give the pilip time to heal before deciding the further treatment required. Classification based on Location of Fabrication 4,9 Materials can be classified based on the location of fabrication into: ⢠Direct restorative materials. ⢠Indirect restorative materials Direct restorative materials: They include those materials which are used to restore cavity preparations directly in the oral cavity (Box 1.5). Box 1.5: Examples of direct restorative materials Amalgam, composites, glass ionomer and other materials, which set by chemical reactions in the mouth. Indirect restorative materials: It includes those restorations which must be fabricated outside the mouth, indirectly on a cast/ model/ die, because their processing condition would harm oral tissues. Materials used in the construction of such prosthesis are called indirect restorative materials (Box 1.6). Box 1.6: Examples of indirect restorative materials Gold inlays, crowns of metal, ceramic and polymers, which are processed at elevated temperatures. Some indirect composite restorations can be processed under specific wavelength of light, e.g. Ceramage. Classification based on Longevity of Use 1. Permanent restorations: These restorations are not planned to be replaced for a particular time period. Though they are referred to as permanent, actually they are not, e.g. fillings, crowns, bridges and dentures do not last forever (Fig. 1.5). 2. Temporary restorations: These restorations are planned to be replaced in a short period of time, such as few days to weeks. For ~ Permanent C/) c c -.2 0 c- :;::; Cll co Interim ~ Q; 0 .8ll::1iJ C/) o~ Cll a:: c:=:J Temporary Time period Fig. 1.5: Diagram depicting the time period of use of a restoration. (Arrow in permanent restoration depicts that such restorations are not planned to be replaced for a long period of time.) Introducton to Dental Materials Dental materials Box 1.7: Characteristics of metals 1. High thermal and electrical conductivity 2. Ductility (pure metals are very soft and they can be bent without breaking) 3. Opacity (they do not transmit light) 4. Luster (they have a surface that strongly reflects light and appears bright and shiny) 5. They tend to dissolve to some extent in water or other aqueous solutions, producing cations. 6. All metals are white (actually gray) except for gold, which is yellow, and copper, which is reddish. 7. All metals are solid at room temperature except mercury, which is liquid at room temperature and is used with silver alloys as amalgam. 8. All metals have high melting temperatures because of high strength of the metallic bond that holds the atoms together. 3. Polymers 4. Composites Composites are mixtures of two or more of the first three classes in which the different components remain distinct from one another in the final structure. A common example is composite resin. Fig. 1.7a: Three-dimensional structure of iron (metal) Metals Metals are the oldest of the three classes of materials that have been used as dental materials. Metals are characterized by metallic bonds (Box 1.7) which will be discussed in the next chapter. Metals solidify with their atoms in a regular or crystalline arrangement (see Chapter 2), often in the form of a cube (Fig. 1.7a). example, temporary fillings done in a tooth during root canal treatment, which have to be replaced within 2-4 days during subsequent visits. They are used to protect the tooth and provide function till the final restoration is done. 3. Interim restoration: At times, dental treatment requires "long-term" definite temporary restorations or "interim" restorations. For examle, a 7-year-old child, met with trauma and fractured one of his central incisors. A large composite build- up may serve his immediate requirement until the root formation is completed and a permanent crown is placed. 5 Classification based on the Chemical Nature of the Material These are the atoms that make up a material and the way they are bonded together determine the properties of that materiaLS Weak bonds make for weak materials and vice versa (Table 1.4). Materials can be classified into different categories based on their primary atomic bonds (Fig. 1.6): 1. Metals 2. Ceramics Fig. 1.6: Classification of dental materials based on chemical nature 12 Basis of Material Science Box 1.9: Benefits of ceramics in dentistry 1. Many ceramic oxides are used as pigmenting agents. These oxides produce good range of colors. Due to this characteristic, we are able to match almost any tooth color with good esthetic results. 2. They are inert, i.e. not chemically reactive. This quality provides ceramics with good bio- compatibility. 3. Ceramic materials are translucent, like natural teeth. This translucency gives the ceramic crown a more natural appearance than any other dental material. Fig. 1.7b: Internal arrangement of tetrahedral structure of ceramic (silica) four large oxygen atoms surround smaller silicon atom Ceramics A ceramic is a compound formed by the union of a metallic and a non-metallic element (Box 1.8). Most of these materials are oxides, formed by the union of oxygen with metals such as silicon, aluminum, calcium and magnesium (Fig.1.7b). Ceramics may be simple or complex. Examples of simple ceramics are alumina and silica. Examples of complex ceramics are feldspar (potassium aluminum silicate) and kaolin (hydrated aluminum silicate). Ceramics may be crystalline or non- crystalline (i.e. amorphous). Porcelain is a specific type of ceramic used extensively in dentistry (Box 1.9). Box 1.8: Characteristics of ceramics 1. High melting points. 2. Brittleness, which means they cannot be bent or deformed (no sliding) to any extent without actually cracking and breaking. 3. They are poor conductor of heat and electricity. 4. They are chemically inert. 5. They have excellent esthetic result in terms of matching natural teeth. Fig. 1.8: Stucture of synthetic polymer Polymers They are the latest addition (early to mid- 1900s) to dental materials. Most of the polymers are nowadays synthesized by humans. Polymers are giant, long-chain organic molecules (Fig. 1.8). Polymers are characterized by covalent bonds within each molecule, giving them tremendous strength in a single direction. Try to break a nylon rope by pulling it! They are poor conductors of heat and electri- city. Most polymers have a structure containing thousands of carbon atoms linked together like beads on a string. Others, such as silicone polymers are formed with silicon-oxygen bonds. Introducton to Dental Materials Table 1.4: Characteristics of different materials 13 Characteristics Bond Properties Crystal structure Metals Metallic bonding High strength and hardness, high electrical and thermal conductivity BCC, FCC, or HCP unit cells Ceramics Ionic or covalent bonding, or both High hardness and stiffness, electrically insulating, refractory, and chemically inert Crystalline or amorphous Polymers Covalent bonding Low sensitivity, high electrical resistivity, and low thermal conductivity, strength and stiffness vary widely Amorphous and crystalline Composites Composites are combinations of any of the basic ceramic, metallic and polymeric materials (Box 1.10). Each material that makes up composites is called a phase. Their properties tend to be somewhere between those of their basic constituents and are used to enhance their performance, longevity and handling chracterstics. Box 1.10: Types of composites in dentistry 1. Ceramic - metallic composite: Tungsten carbide bur. 2. Metal - polymer composite: Die materials in dental laboratory. 3. Ceramic - polymer composite: Enamel, dentin, bone and restorative composites. A composite is a kind of "combination" of materials, which compliment each other. The properties lacking in one material are compensated by those of the other material. For example, restorative composite has two phases, namely resin and fillers. Teeth and bones are examples of natural composites. Enamel is a composite of hydroxyapatite (which is a ceramic material) and protein (which is a polymer). EVALUATION OF DENTAL MATERIALS Most manufacturers of dental materials maintain a quality assurance programme (As per international standard like ADA specifications) and materials are thoroughly tested before being released into the market for dental practitioner (Fig. 1.9). Laboratory Evaluations Most ADA/ ANSI specifications involve laboratory tests. The tests performed as per these specifications are useful but they all are performed in vitro, (carried out in the laboratory away from the clinical conditions) which have a lot of limitations in clinical practice.lO Clinical Notes 1. For example, most of the direct restorative materials are tested for their compressive strength but ultimately the material is subjected to a combination of compressive, tensile and shear stresses, which may decide the final success or failure of the material under masticatory load. 2. Similarly upper dentures mostly fracture along the midline because of bending. Hence a bending or transverse strength ~B-a-s-is-o-f-M-a-t-e-ria-I-S~c-ie-n-c-e-------------- ---------. test is far more meaningful for denture base materials than a compression test. Clinical Trials The majority of new materials are subjected to extensive clinical trials normally in co-operation with a dental college or hospital departments prior to their release. CONCLUSION As the number of available materials is going up, it is important that the dentist remains more aware about new products so that their judgement about the selection of material remains successful. Materials which have not been thoroughly evaluated should be avoided, specially with clinical dentistry falling under Consumer Protection Act (CPA). I Research and development I iI Manufacturer/analysis Ideal requirements for clinical use: Thermal, optical, mechanical, chemical, biological Available materials and their properties are evaluated Launch of new I product Choice and selection of material by the dentist Critical assessment based on clinical performance I I H feedback to I
Ions Ions are charged substances that have formed through the gain or loss of electrons. Cations form from the loss of electrons and have a positive charge while anions form through the gain of electrons and have a negative charge. Cation Formation Cations are the positive ions formed by the loss of one or more electrons. The most commonly formed cations of the representative elements are those that involve the loss of all of the valence electrons. Consider the alkali metal sodium (Na) . It has one valence electron in the n=3 energy level. Upon losing that electron, the sodiu ion now has an octet of electrons from the second energy level and a charge of 1+ . The electron arrangement of the sodium ion is now the same as that of the noble gas neon. Consider a similar process with magnesium and aluminum. In this case, the magnesium atom loses its two valence electrons in order to achieve the same arrangement as the noble gas neon and a charge of 2+ . The aluminum atom loses its three valence electrons to have the same electron arrangement as neon and a charge of 3+ . For representative elements under typical conditions, three electrons is usually the maximum number that will be los. Representative elements will not lose electrons beyond their valence because they would have to "break" the octet of the previous energy level which provides stability to the ion. Anions Anions are the negative ions formed from the gain of one or more electrons. When nonmetal atoms gain elections, they often do so until their outermost principal energy level achieves an octet. For fluorine, which has an electron arrangement of (2, 7), it only needs to gain one electron to have the same electron arrangement as neon. Forming an octet (eight electrons in the outer shell) provides stability to the atom. Fluorine will gain one electron and have a charge of 1ā . The electron arrangement of the fluoride ion (2, 8) will also change to reflect the gain of an electron. Oxygen has an electron arrangement of (2, 6) and needs to gain two electrons to fill the n=2 energy level and achieve an octet of electrons in the outermost shell. The oxide ion will have a charge of 2ā as a result of gaining two electrons. Under typical conditions, three electrons is the maximum that will be gained in the formation of anions. Subatomic Particles in an Ion Since ions form from the gain or loss of electrons, we can also look at the number of subatomic particles (protons, neutrons, and electrons) found in an ion. Remember that the number of protons determines the identity of the element and will not change in a chemical process. Example 2.5.1 How many protons, neutrons, and electrons in a single oxide (O2ā) ion? Solution Oxygen has the atomic number 8 so both the atom and the ion will have 8 protons. The average atomic mass of oxygen is 16. Therefore, there will be 8 neutrons (atomic massāatomic number=neutrons) . A neutral oxygen atom would have 8 electrons. However, the anion has gained two electrons so O2ā has 10 electrons. We can also use information about the subatomic particles to determine the identity of an ion. Example 2.5.2 An ion with a 2+ charge has 18 electrons. Determine the identity of the ion. Solution If an ion has a 2+ charge then it must have lost electrons to form the cation. If the ion has 18 electrons and the atom lost 2 to form the ion, then the neutral atom contained 20 electrons. Since it was neutral, it must also have had 20 protons. Therefore the element is calcium. Polyatomic Ions A polyatomic ion is an ion composed of two or more atoms that have a charge as a group (poly = many). The ammonium ion (see figure below) consists of one nitrogen atom and four hydrogen atoms. Together, they comprise a single ion with a 1+ charge and a formula of NH+4 . The hydroxide ion (see figure below) contains one hydrogen atom and one oxygen atom with an overall charge of 1ā . The carbonate ion (see figure below) consists of one carbon atom and three oxygen atoms and carries an overall charge of 2ā . The formula of the carbonate ion is CO2ā3 . The atoms of a polyatomic ion are tightly bonded together and so the entire ion behaves as a single unit. The figures below show several examples. Soult Screenshot 2-2-1.png Figure 2.5.1 : The ammonium ion (NH+4) is a nitrogen atom (blue) bonded to four hydrogen atoms (white). Soult Screenshot 2-2-2.png Figure 2.5.2 : The hydroxide ion (OHā) is an oxygen atom (red) bonded to a hydrogen atom. Soult Screenshot 2-2-3.png Figure 2.5.3 : The carbonate ion (CO2ā3) is a carbon atom (black) bonded to three oxygen atoms. The table below lists a number of polyatomic ions by name and by structure. The heading for each column indicates the charge on the polyatomic ions in that group. Note that the vast majority of the ions listed are anions - there are very few polyatomic cations. 1ā 2ā 3ā 1+ Table 2.5.1 : Common Polyatomic Ions acetate, CH3COOā carbonate, CO2ā3 arsenate, AsO3ā3 ammonium, NH+4 bromate, BrOā3 chromate, CrO2ā4 phosphite, PO3ā3 chlorate, ClOā3 dichromate, Cr2O2ā7 phosphate, PO3ā4 chlorite, ClOā2 hydrogen phosphate, HPO2ā4 cyanide, CNā oxalate, C2O2ā4 dihydrogen phosphate, H2POā4 peroxide, O2ā2 hydrogen carbonate, HCOā3 silicate, SiO2ā3 hydrogen sulfate, HSOā4 sulfate, SO2ā4 hydrogen sulfide, HSā sulfite, SO2ā3 hydroxide, OHā hypochlorite, ClOā nitrate, NOā3 nitrite, NOā2 perchlorate, ClOā4 permanganate, MnOā4 The vast majority of polyatomic ions are anions, many of which end in -ate or -ite. Notice that in some cases such as nitrate (NOā3) and nitrite (NOā2) , there are multiple anions that consist of the same two elements. In these cases, the difference between the ions is the number of oxygen atoms present, while the overall charge is the same. As a class, these are called oxyanions. When there are two oxyanions for a particular element, the one with the greater number of oxygen atoms gets the -ate suffix, while the one with the fewer number of oxygen atoms gets the -ite suffix. The four oxyanions of chlorine are shown below, which also includes the use of the prefixes hypo- and per-. ClOā , hypochlorite ClOā2 , chlorite ClOā3 , chlorate ClOā4 , perchlorate Not your usual ion Soult Screenshot 2-2-4.png "Drink you milk. It's good for your bones." We're told this from early childhood, and with good reason. Milk contains a good supply of calcium, part of the structure of bone. However, there are two other ionic components of hydroxyapatite, the mineral component. Phosphate ion and hydroxide ion make up the remainder of the inorganic material in bone. News You Can Use Bone is a very complex structure. It is composed of protein (mainly collagen), hydroxyapatite (a calcium-phosphate-hydroxide mixture), some other minerals, and contains 10 - 20% water. The calcium/phosphate ratios are not stoichiometric, but vary somewhat from one portion of bone to the next. Bones are very strong but will break under enough stress. Regular exercise and proper nutrition help to increase bone strength. Watch a video about bone structure at http://www.youtube.com/watch?v=d9owEvYdouk Nitrate is an anion with a complex bonding structure. Major sources for this ion in drinking water are runoff from fertilizer, septic tank leakage, sewage, and natural deposits. High concentrations of nitrates represent a significant health hazard, especially to infants. The nitrate in the body is converted to nitrite, which then binds to hemoglobin. This binding decreases the ability of hemoglobin to transport oxygen, thus depriving the cells of the O2 needed for proper functioning. Cyanide production is widespread throughout nature. Forest fires will produce significant amounts of cyanide. Many plants contain cyanide, and it is produced by a number of bacteria, algae, and fungi. Cyanide is used industrially in metal finishing, iron and steel mills, and in organic synthesis processes. This material is also an important component for the refining of precious metals. Formation of a complex between cyanide and gold allows extraction of this metal from a mixture.