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Flashcards by Chima Power, updated more than 1 year ago
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Created by Chima Power
over 10 years ago
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| Question | Answer |
| Compound | Two or more elements chemically bonded together |
| Covalent bonding | Sharing electrons to have full outer shell for atoms |
| Ionic bonding | Transferring electrons to form a full outer shell for atoms |
| Giant structures | Ions formed are held together by strong electrostatic forces of attraction between the oppositely charged ions, the ionic bonds between the charged particles results in giant structures or giant lattices. The giant structure is held so strongly together because the force exerted on an ion by another ion is equal in all directions. Also this structure is very large because the ions can pack neatly in rows |
| Ionic formulae | Brackets are used, sometimes to show ratios of elements in compounds, the ionic formulae shoes the ratios of elements in a compound and charges in ionic compounds always cancel out |
| Simple molecules | Gain electronic structure of a noble gas by sharing electrons to gain a full outer shell held together by shared electrons hence said have strong bonds between the atoms are called covalent bonding. Sometimes more than one atom is involved |
| Giant covalent structure | In these giant structures the huge number of atoms are held together by a network of covalent bonds sometimes reffered to as macromolecules forms lattice such as diamond and silicon dioxide |
| Metal crystals | metals are built in layers in a regular pattern, means they form crystals sometimes we can see them such as zinc crystals |
| metallic bonding | metals are examples of giant structures can be thought of a lattice of positively charged ions as arranged in regular pattern one on top of another. Have delocalised electrons, outer electrons that are free to move, strong electrostatic attraction between the negatively charged and positively charged ions bond metal ions to each other electrons act like glue |
| Ionic compounds | When melted electricity can pass through as ions have more movement also ionic compounds will dissolve in water as the lattice breaks up the ions can move freely in the solution and can also conduct electricity and the ions will move towards the oppositely charged ion. |
| Simple molecules structure | many have low boiling and melting such that they are liquids and gases at room temperature. This is due to the fact although they are strong covalent bonds so the atoms within molecules are held tightly together however the molecules seem to not be strongly bonded therefore they have low intermolecular forces so overcoming these does not take much energy. At liquid will not conduct electricity as no charge. |
| Giant covalent structures explained | held in position by strong covalent bonds so have high melting and boiling points, are very hard and are insoluble in water |
| Carbon | Diamonds are espically hard as each carbon atom forms four covalent bonds. In graphite, carbon atoms only have three covalent bonds hence forms hexagonal shapes arranged in giant layers. there are no covalent bonds between layers so the layers can slide over each other easily makes graphite a soft material that feels slippery as have low intermolecular forces between layers. This three covalent bonds leave delocalised electron so can conduct electricity unlike diamond and other covalent bonds. |
| Fullerenes | Other than diamond and graphite carbon can form in these structures join together to form large cases which can have all kind of shapes such as balls, onions and tubes built up of hexagonal rings of carbon atoms. These kind of carbon structures called fullerenes. Can place other molecules in these structures possibilities such as delivery of drugs to particular parts of the body and are believed to important to nano science explanation in lubricants and catalysts. |
| Giant metallic structures | You can hammer and bend metals into different shapes as their layers are easily able to slide over one another. The atoms in a pure metals are held together in a giant metallic structure so that the atoms are arranged in closely packed layers. Alloys are a mixture of metals so there are different sizes of atoms in an alloy making it difficult in the structure to slide over each other so that they are harder than their corresponding pure metals |
| Shape memory alloys | These alloys can be bent and deformed into different shapes but when they are heated up they return to their original shape called shape memory alloys as seem to remember their own shape. Can be used in many procedures for instance health care when doctors treat a badly broken bone the alloys hold the bone in place while they heal they cool they alloy before it is wrapped around the broken bone when it heats up again it pulls the bone together while it heals |
| properties of polymers | These depend on the monomers used to make it and the conditions we choose to carry out this reaction |
| Different monomers | nylon polymers made of two different monomers one with acidic groups at each end the other with basic groups at each end. Polymer made very different from monomers such as hydrocarbon so monomers used make a big difference. |
| different reaction conditions | For example same monomers used in LD (low density) polyethene as HD (high density) there is a difference beacause of the different reaction conditions. LD is produced in high pressure with a trace of oxygen conditions branched chains and loose. While HD is formed using a catalyst at 50c and slightly raised pressure pack more closely and straight. HD higher softening temperature and stronger than LD |
| Thermosoftening polymers | classification of polymers occurs from what temperature they soften. Some will soften quite quickly, they will reset when they cool these are called thermosoftening polymers made up of individual polymer chains that are tangled together. |
| Thermosetting polymers | Polymers that do not melt when we heat them have strong covalent bonds forming cross links between their polymer chains like a brick wall. |
| Bonding in polymers | Atoms in polymer chains are held together by strong covalent bonds true for all plastics although the size of the forces between polymer differs in plastics. |
| Thermosetting polymers | Monomers make covalent bonds between the polymer chains when first heated in order to shape them. Covalent bonds are strong and can stop polymers from softening due to cross link if enough heat plastic will char |
| Nanoscience | Nano means one thousand-millionth 1nm =1*10^-9. This is dealing with structures that are just a few hundreth atoms in size or even smaller between 1nm and 100nm. These materials behave differently at there very tiny scale. nanoparticles are so small they have a large surface area for their volume, can create remarkable properties. |
| Nanoscience at work | -Glass can be coated with titanium oxide nanoparticles sushine triggers a chemical reaction that breakdowns the dirt that lands on the window. When it rains water spreads evenly over the window washing away the broken down dirt - Titanium oxide and zinc oxide nanoparticles used in modern sun screens. Scientists can coat nanoparticles of metal oxide with a coating of silica. Silica coating can be thickness can be adjusted at an atomic level. Seem to be more effective - cosmetics industry one of the biggest in face creams they are absorbed deeper in the skin, used in sun tans and deodrants. |
| Nano science in medicine | Delivery of active ingredients in cosmetics can be applied to medicine. Latest technique use gold nano cages to deliver drugs to where they need to go. Researchers have found that tiny gold particles can be injected and absorbed by tumors. As tumors have thin leaky blood vessels with holes large enough for gold particles to pass through. Can not pass through healthy blood vessels. When a laser is directed at the tumor the gold nano particles which absorb energy and warm up. The temperature increases enough to change the properties of the polymers but barely warm the surronding tissue. This destroys the tumour cells without damaging healthy cells. Potential to use gold nanocages to carry cancer fighting drugs to the tumour at the same time the carbon nanocages can also be used. Nanotubes are incredibly strong yet light being used to reinforce materials like in sport tennis racquets. silver nanoparticles are antibacterial used against bacteria and fungi and cleaning operating theartres in hospitals. |
| Future developments of nanoscience | Being developed to be used as nanwires which can be used to construct incredibly small electric circuts. Nanotubes can be used to construct highly sensitive sensors. For example detect gas particles in asthmatics. Nanowires would also help improve computers speed and capacity. US army is developing of nanotech suits- thin or even spray on uniforms which are flexible and tough enough to withstand bullets and blasts. Uniforms would receive aerial views of the battlefield from satellites transmitted directly to soldiers brain. Built in air conditioner, full range of nanobiosensors that could send medical data to medical team. |
| Possible risks of nanoscience | Large surface area of nano particles would make them useful as catalysts but this also makes them dangerous if a spark occurs a violent explosion could erupt. More used could contaminate air and damage lungs could have unpredictable effect if enter bloodstream. |
| Isotopes | These are atoms of the same element that have a different number of neutrons. Always have the same atomic number but different mass number. Sometimes the extra neutrons make the nucleus unstable so radioactive however not for all isotopes they are just atoms of the same element with different masses. Physical properties differ as have different density and may be raidoactive. Chemical properties do not change electronic structure for elements of an isotope are same as depends on the amount of electrons. |
| Relative atomic mass (Ar) | The mass of a single is so impractical that it is not used in calculations instead of using the actual masses we use the relative masses of different elements. We use an atom of carbon-12 as a standard atom so used as the base. Given a mass of exactly 12 units as has 6 protons and 6 neutrons, we can then compare this to other atoms of all the other elements. The relative atomic mass for an atom is usually similar to the mass number of its most common isotope. The relative atomic mass takes into account the proportions of any isotopes of the element found naturally so it is an average mass compared with the standard carbon atom so decimals can occur. |
| Relative formula masses (Mr) | Use the relative atomic mass of various element to work out the relative formula mass of a compound. add the relative atomic masses of the elements if more than one element act accordingly. Example: H20= 2*1 + 16=18 |
| Moles | Writing relative atomic mass in grams is not well presented so another word for this is moles. Say that the relative atomic mass in grams of carbon (12g) is a mole of carbon atoms. A mole of any atom always contain the same number of atoms, molecules or ions, huge number 6*10^23. One mole is simply the relative atomic mass or relative formula mass expressed in grams. |
| percentage of an element in a compound equation | first find the formula of the compound and then the relative atomic masses of the elements in the compound. Add these together to find the relative formula mass. You then figure out the mass of the desired element as a fraction by doing: relative mass of element/ total mass of compound. then times by 100 to find as percentage. |
| Empirical formula of compounds from it's percentage composition | The empirical formula is the simplest (whole number) ratio of atoms in a compound. Find this by working out the percentage of each element in a compound by experiments and then find this is it's simplest ratio. To work out the formula from percentages masses: Change the percentages given to the masses of each element in 100g of compound Change the masses into moles of atoms by dividing the masses by the Ar values. Tells you how many moles of the different element are present. Tells you the ratio of atoms of the different elements in a compound |
| Using balanced equations to work out reacting masses | First find out Ar of elements in compound then multiply Ar by amount of element in compound and then add up to find total |
| Yield of chemical reaction | The amount of product that a chemical reaction produces is it's yeild |
| Percentage yield | This compares the amount of products that could be produced with the amount that is produced. Percentage yield=amount of product produced/ maximum amount of product produced *100% |
| Reasons why percentage yield is unlikely to be 100% | The reaction may be reversible so reactants produces in process of reaction Some reactants may give unexpected products Some of the products may be lost in handling or left behind in the apparatus The reactants may not be completely pure More than one product may be produced where there is a difficulty to separate it from the reaction mixture |
| Sustainable production | Chemical companies want greatest percentage yield to increase efficiency and limit waste. Plants are designed by enginners to limit use of raw materials and energy to save money also good for environment. |
| Reversible reactions | There is where in a reaction the products can react together to make the original reactants again. Drawn with two arrow signs going forward and backward. |
| Examples of reversible reactions | Litmus complex molecule, H (Hydrogen) and Lit react together in acid to turn red but in alkaline the turn back into their reactants and as Lit is blue the substance becomes blue. Ammonium chloride thermally decomposes when cool the ammonium and hydrogen chloride again react. |
| Detective additives: Chromatograhy | An food additive is a substance that improves foods longevity, appearance or taste. A method for detection of additives is chromatography works because some compounds dissolve better than other in particular solvent. Solubility depends on how far they travel across the paper. Once seperated can be identified using known substances but same solvent must be used at same temperature. |
| Detecting additives: Instrumental methods | Type of analysis common in health care Benefits: Highly accurate and sensitive Quicker Enable very small capsules to be analysed Drawbacks: Usually more expensive Takes special training to use Gives results that can only usually be determined by comparison with data from known substances |
| Gas chromatography | Separation method similar to paper chromatography however instead of paper it is a gas moving through a tube packed with solids. First of all sample vaporized then vapor is carried through coiled column by a carrier gas. The compounds in the sample have different attraction strengthens so compounds move through the column at different speeds we say have different retention time. The lower the attraction the lower the retention time. Can identify the unknown in the samples by comparing the chromatography with results for known substances, analysis must have taken place in exactly same conditions to compare retention time. |
| Mass spectometry | Ensures that we identify the unknown substances the gas chromatography can be directly attached to the mass spectrometer. Identifies substances quickly and accurately and can identify small substances. Also provides an accurate way of measuring the relative molecular formula mass of a compound. Peak with the largest mass corresponds to ion with just one electron missing, peak is called molecular ion peak. Always found as the last peak on the right as you look at the mass spectrum. Acts like a fingerprint. |
| Rate of reactions | This is the speed at which products of a chemical reaction are produced from the reactants occurs in the body, important in chemical industry as if too slow produce not profitable. We can find the rate of a reaction by finding out how quickly the reactants are used up or products are produced. We can also measure the rate at which the mass differs if the reaction gives of gas. If gives of gas can also measure how much gas is given off by collecting the gas and measuring the volume at regular intervals. Some reactions in solution make an insoluble solid precipitate, go cloud, can measure the rate at which the solid disappears by recording time taken for cross on paper underneath solution disappears or using light sensors and data loggers. Light sensors can record the change overtime. Rate of reaction = amount of reactant used/ time |
| Factors affect the rate of a reaction | Temperature Surface area Concentration of solution or pressure of gases Presence of catalysts |
| Collision theory | Reactions can only take place when particles come together need enough energy to react when they collide. The smallest amount of energy that particles must have to react is called activation energy. Reactions are more likely: Increase the chance of particles colliding Increase the energy they have when they collide. |
| Surface area and reaction time | The larger the surface the faster and more likely the reaction is for example making a fire as particles in a large lump must have particles on surface react first. This is because it increases the number of collisions. |
| Effect of temperature of reaction time | Increase in temperature leads to increased rate of reaction because particles collide with more energy and at a greater frequency. When heated particles more around with more energy hence speed so collide more often so more chances for them to react increases rate of reaction. More energy means a higher proportion of particles have more energy than activation energy so higher proportion of collisions result in more reactions take place. |
| Effect of concentration on reaction time | Increasing the concentration of reactants in a solution increases the rate of a reaction because there are more particles in the same volume so collision occur at a higher proportion resulting in a faster rate of reactions. |
| Effects of catalysts on reaction time | Saves industry money as alternative to high pressure of temperature. A catalyst is a substance that speeds up the rate of a reaction without being changed itself so can used over and over again. different catalysts are used for different reactions, many of the catalysts used in industry involve transition metals. Normally used in form of powders, pellets or fine gauze's gives them greatest surface area. Also help the environment but most are transtion metals or their compounds so can be toxic to environment if contimated so scientists developing new methods bu trial and error and then minor improvements, consumes time. |
| Future development of catalysts | Chemists have developed new techniques to look at reactions can now follow the reactions that happen on the surface of the metals in a catalytic converter as they are very fast acting in only a fraction of a second. Knowing how reactions take place will help make new catalysts. Nanoparticles can also be used as new catalysts, scientists can arrange atoms in the best shape for catalysing a particular reaction they have studied. A small mass of these catalysts have a huge surface are. Has hopes fuel cells will take over petrol and diesel |
| Catalysts in medicine | Catalysts used in making new drugs contains precious metal properties, metal is bonded to organic molecule, but know chemists can make these catalysts without metal. As before the metal was needed to make a stable compound but research has lead to breakthrough that means cheaper catalysts and no risk of toxic transitions metals contaminating the drug. |
| Enzymes as catalysts | These are very efficient catalysts made of living things used as detergents for clothes helping to remove biological stains at low temperature so saving energy. This is the basis for the biotechnology industry, enzymes are soluble so have to separated from the products, although scientists can bind them to a solid. The solution of the reactants flow over the solid, so can be used again without time or money consumed. |
| Exothermic reactions | These are reactions where energy is transferred form the reactants to the surroundings, usually heating up the surrounding so change in temperature can be measured. Examples are combustion, respiration and neutralisation |
| Endothermic reactions | This is a reaction where energy from the surroundings are transferred to the reactants, causing a drop in temperature from the surroundings. Although less common examples are thermal decomposition such as calcuim carbonate |
| Reversible reaction | Between the reactants and products one are endothermic and other exothermic so that no additional energy is required for the reaction to occur such as copper sulfate crystals hydration which is an endothermic reaction. |
| Energy transfers from reactions: Warming up | Chemical hand and body warmers can be useful as use exothermic reactions to heat up people. Can be used in cold places like stadium or help warm aches and pains. Some can only be used once but are more effective like oxidation of iron which usually lasts hours. However some can also be reused based on forming crystals from a solution of salt. Done by first a supersaturated solution being prepared by dissolving as much salt possible in hot water, solution is then allowed to cool. Small metal disc in in the plastic pack used to start reacton when pressed small metal particles scraped off start the crystalisation, crystals spread throughout the pack giving of heat. To reuse just dissolve in hot water and cool. |
| Exothermic reactions self heating cans | Reaction used to release energy: calcium oxide + water => calcium hydroxide Button pressed causes a seal to break and the two reactants to react used to heat up coffee took long to develop |
| Endothermic reactions cooling down | Chemical cold packs usually contain ammonium nitrate and water, when the ammonium nitrate dissolves it takes in energy from the surroundings, making them colder. Used for sport injuries, reducing swelling and numbs pain. Works about 20 min can be strarted by squeezing or strucking cold pack. Can only be used once and can be used to cool cans |
| Aqueous solution | This is a substance dissolved in water that is either acidic, neutral or alkaline depending on the substance dissolved. |
| Alkalis | These are soluble hydroxides their solution are called alkaline example is soduim hydroxide solution. Often used as bases in experiments sodium hydroxide solution often found in school labs, attain by dissolving solid sodium hydroxide in water. |
| Bases | These include alkalis, these neutralise acids. Metal oxides and metal hydroxides are bases, example iron oxide and copper hydroxide. |
| Acids and neutral | These include citric acid, sulfuric acid and ethanoic acids. All acids taste very sour. Pure water is neutral. Hydrochloric acid commonly used in science class is formed by the gas hydrogen chloride dissolving in water. HCl(g) --> H+(aq) + Cl-(aq) Also forms chloride ions (Cl-) aq in solution called state symbol, shows ions are in aqueous solution ( dissolved in water). |
| Measuring acidity or alkalinity | Using indicators which are substances that change color when you add them to acid or alkali, litmus is a commonly used one. Can use pH scale to see how acid or alkali a substance is 0 is very acid and 14 is very alkali so 7 is neutral. Can use a universal indicator which is a mixture of many dyes which turns the color according to the acidity or alkalinity of a substance in reference to the pH scale. |
| Making salts | Salts can be made by mixing metals with acids, only possible if metal is more reactive than hydrogen, if so metal will react with acid to form salt as well as hydrogen gas: acid + metal -> a salt + hydrogen Hydrochloric acid + Magnesium -> Magnesium chloride + hydrogen. If metal too reactive reaction will be too violent to carry out safely like pottasium. Acid + base -> a salt + water a neutralisation occurs. |
| Making salts from acids and alkalis | acid + alkali -> a soluble salt + water HCL + NaOH(aq) -> NaCl(aq) + H2O Neutralisation of the two reactants causes water to form: H+ + HO- -> H2O nitric acid + ammonia nitrate -> ammonuim nitrate + water Contains a high proportion of nitrogen and soluble in water so is a good nitrogen source for plants and replaces the nitrogen in soil taken by plants as they grow. Can detect ammonia unreacted by using a using a universal indicator. When crystalised excess ammonia will evaporate. |
| Making insoluble salts | Sometimes salts can be made by reacting two soluble salts, when soluble salts react and produce insoluble salts called a precipitation reaction because insoluble solid formed is called a precipitate. lead nitrate solution + potassium iodide solution -> lead iodide precipitate + potassium nitrate solution Each of the reactant solution contains one of the ions of the insoluble salt |
| Using precipitation | Can be used to remove pollutants from the waste water from factories, must be treated before discharged into rivers and the sea. Used in removal of metal ions from industrial waste water, done by raising the pH of the water which causes insoluble metal hydroxides to precipitate out. Producing sludge which can easily be removed from the water. Can also be used to remove unwanted ions from drinking water. |
| Electrolysis | Process of using an electric current to break down an ionic substance. Substance broken down is called an electrolyte. To set up such a reaction there must be two electrodes dipped in the electrolyte. One electrode is connected to the positive terminal of the power supply while the other is connected to the negative terminal of the power supply. Electrodes made of nonreactive (inert) substances so do not react with electrolyte or products. During electrolysis the positively charged ions are attracted to the negatively charged electrode while the negatively charged ions are attracted to the positively charged electrode. When the ions reach the electrode they lose their charge and become elements. Gases may be given off or metals deposited by the electrode dependent on the compound and whether molten or dissolved in water. Ionic substances do not conduct electricity when solid. |
| Electrolysis of solutions | Many ionic substances have high melting points which can make electrolysis problematic. However some ionic substances can be dissolved in water so that their ions are free to move around. However when electrolysing solutions products are difficult to predict as water also forms ions. Covalent compounds cannot usually be electrolysed unless they react in water to form compounds. |
| Changes at electrodes | Gaining is called reduction it is said positive ions to become neutral are reduced, gain electrons. Negatively charged ions lose electrons to become elements, loss of an electron is called oxidation. Say that negatively charged ions are oxidised. Can represent what happens at each electrode using half equations to show loss or gain of electrons. |
| Effect of water on electrolysis | In aqueous solutions electrolysis is more complex because of the ions from water. Rule for working out what will happen: If two elements can be produced at an electrode the less reactive element will usually be formed. At negative electrode Least reactive discharged halide ion> hydroxide> all other negatively charged ions. At positive electrode oxygen gas is given off because oxygen discharged. |
| Extraction of aluminium | Aluminum is quite reactive so carbon cannot be used therefore electrolysis must be used compound electrolysed is aluminum oxide. aluminum oxide is attained from bauxite ore so first must be separated from impurities, containing a lot of iron oxide. This colours the waste solution from the separation process rusty brown, solution must be stored in large lagoons. To electrolyse aluminium oxide must first melt it so ion can freely move around.However aluminium has a very high melting point 2050c but by adding molten cryolite it can be electrolysed at 850c eletrical energy keeps the mixture molten. |
| Extraction of aluminium | Aluminum is quite reactive so carbon cannot be used therefore electrolysis must be used compound electrolysed is aluminum oxide. aluminum oxide is attained from bauxite ore so first must be separated from impurities, containing a lot of iron oxide. This colours the waste solution from the separation process rusty brown, solution must be stored in large lagoons. To electrolyse aluminium oxide must first melt it so ion can freely move around.However aluminium has a very high melting point 2050c but by adding molten cryolite it can be electrolysed at 850c eletrical energy keeps the mixture molten. |
| Reaction at electrolysis cells | Overall reaction: aluminium oxide -> aluminium + oxygen At the negative electrode: Each aluminum gains 3 electrons, reduced, to become an aluminium atom, the aluminum metal is molten and collected at the bottom and then siphoned or tapped off. At the positive electrode: Oxide ion lose two electrons oxidised to form oxygen atoms bond in pairs to form oxygen gas, react with carbon electrons to form carbon dioxide gas, so positive electrode burns away and must be replaced. An aluminium plant uses as much energy as a small town. |
| Electrolysis of brine | Brine is concentrated sodium chloride solution, it is a very important industrial process. At the positive electrode: Negative chloride ions are attracted to positive electrode they lose an electron so oxidised, chlorine atoms bond together in pairs and given off as chloride gas. At the negative electrode: There are hydrogen atoms in brine formed when water breaks down these are attracted to negative electrode, sodium ions are also attracted to the negative electrode. As hydrogen less reactive becomes discharged while sodium stays in solution. Hydrogen ions becomes reduced and form in pairs to form hydrogen gas. Remaining solution: Solution is alkaline because chlorine and hydrogen ions are removed which are acid, leaves a solution sodium hydroxide. |
| Uses of products of electrolysis of brine | Chloride: Chloride reacted with solution of sodium hydroxide makes a solution of bleach, good for killing bacteria, can be used in many other disinfectant as well as plastics such as PVC. Hydrogen: Hydrogen make from electrolysis is particularly pure so useful in food industry margarine made by reacting hydrogen with vegetable oils. Sodium hydroxide: Used to make soap and paper |
| Electroplating | This is an object coated with a thin layer of metal by electrolysis. Uses: Protect metal from being corroded Make the object look more attractive (jewelry) Increase hardness of surface and resistance to scratching Save money by using a thin layer of a precious metal instead of the pure expensive metal Helps people allergic to nickel - metal often made in cheap jewelry. More economic in small objects but will payback eventually. |
| Explaining electroplating | Metal object to be plated is used as the negative electrode, the positive electrode is made of the plating metal. The solution contains nickel ions. At the positive electrode Nickel atoms in the electrode are oxidised lose two electrons forming nickel ions which go into the solution. Nickel ions are reduced gain two electrons and form nickel atoms which are deposited on the copper electrode. |
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