1.1 Identify the industrial source of ethylene from the cracking of some of the fractions from the refining of petroleum
- Ethylene is a versatile raw material industrially sourced from the cracking of some fractions derived from refining of petroleum.
- Petroleum is mixture of crude oil and natural gas/ a mixture of hydrocarbons.
- Fractional distillation is a process that separates petroleum into different fractions of hydrocarbons according to their boiling point. Lighter fractions with lower boiling point rise higher in the column.
- Cracking is a process that splits long chain hydrocarbons into shorter chain molecules. There are two types of cracking:
- Note: Thermal is the main industrial source of ethylene in Australia ∵ Australia’s crude oil is mostly light crude, and thus is high in ethane/propane. Stream is used in thermal for diluting mixture to create smooth reactions and for removing carbon deposits in the metal coils.
- The production of ethylene is summarized in the following flowchart:
1.2 Identify that ethylene, because of the high reactivity of its double bond, is readily transformed into many useful products
Chemical Properties of Alkenes & Alkanes
- Alkenes are unsaturated compounds that have at least one C=C double bond (site of high electron density). This is inherently reactive and thus readily interacts with electronegative species via addition reaction \ Alkenes > alkanes.
- Alkanes are saturated compounds with relatively unreactive single bonds and only reactive via substitution reactions.
Physical Properties of Alkenes & Alkanes
- Alkanes and alkenes are both non-polar ∵ their dipoles are arranged symmetrically such that they cancel each other out and create a zero permanent net dipole. \The strength of their dispersion forces operating is similar. Since physical properties (eg. solubility, bp, mp.) are determined by the strength of intermolecular forces, the physical properties in alkanes and alkenes are similar.
Properties of Ethylene
- Ethylene= alkene → Has a highly reactive C=C double bond → Can easily open out to form to two bonding sites → Can undergo addition reactions (eg. polymerisation, hydrogenation, hydration, hydrohalogenation, bromination, chlorination) → Allows it to produce useful products (eg. polyethylene, ethanol, dibromoethane).
- Ethylene is a monomer that can undergo addition polymerisation to form polyethylene polymers.
- Ethylene may undergo various reactions to form other commercially significant monomers (eg. vinylchloride and styrene).
- These monomers can undergo addition polymerisation to form polymers (eg. poly(vinyl chloride), polystyrene).
- An addition polymer is a long-chain molecule composed of repeating subunits (monomers). Formed when one of the unsaturated bonds in each monomer opens out and the monomers join together.
- In addition polymerisation, there is no loss or gain of atoms. Only one product is formed.
- Polyethylene is an addition polymer ∵ it is the product of the addition polymerisation of ethylene monomers
1.5 Outline the steps in the production of polyethylene as an example of a industrially important polymer
1.6 Identify vinyl chloride and styrene as commercially significant monomers by both their systematic and common names 1.7 Describe the uses of the polymers made from the above monomers in terms of their properties
1.8 Identify data, plan and perform a first-hand investigation to compare the reactivities of appropriate alkenes with the corresponding alkanes in bromine water
To compare the reactivities of cyclohexene with the corresponding cyclohexane in bromine water
Temperature, volume of each hydrocarbon, drops of bromine water, concentration of bromine water, UV light levels
- In a fume hood, pour 2mL of each of the liquids into separate test tubes as shown:
- Add 1 mL of Br2(aq) to test tubes A and B and mix well.
- Observe for 1-2 minutes and record results.
- Repeat steps 1-3 twice.
(Note: Must be conducted in the absence of UV light and Br2(aq) must be the limiting reagent.)
1.9 Analyse information from secondary sources such as computer simulations, molecular model kits or multimedia resources to model the polymerisation process
- Simplifies process and allows students to easily describe or ‘view’ at a molecular level to gain better understanding of the process
- Demonstrates that there is no loss or gain of atoms/ only one product is formed in addition polymerisation.
- Allows students to readily view the spacing difference between low density polyethylene (branched) and high density polyethylene (unbranched).
- Oversimplifies/represents process unrealistically – Does not account for use of Zeigler-Natta catalysts, mobility of electrons, size/distances between atoms and suggests bonds are broken rather than transformed.
2.1 Discuss the need for alternative sources of the compounds presently obtained from the petrochemical industry
- There is an overwhelming need for alternative sources of compounds that are presently derived from the petrochemical industry because of:
- Scarcity of fossil fuels – Consumption of fossil fuels such as crude oil and natural gas, which are non-renewable, has accelerated. These fossil fuels could be completely used up within the next few decades – Statistics suggest Australia’s crude oil reserves will diminish in 10 years and natural gas to last for about 100 years. In addition, as fossil fuel supplies decrease, prices will increase and become too expensive. Thus, renewable and cost-effective substitutes are required.
- Environmental/societal impact – The consumption of petroleum-based fuels eg. octane burn uncleanly relative to fuels from alternative sources such as ethanol, increasing to toxic CO emissions. The non-biodegradable nature of many petroleum-based plastics also places considerable strain on landfills. Thus, alternatives are needed to alleviate such problems.
- Condensation polymer is a long chain formed when the polar bifunctional groups at the ends of monomers react such that a small molecule is released (per two monomer units which react). Examples are:
- Natural: Cellulose, starch, protein, DNA.
- Artificial (manufactured): silk, polyester and nylon.
- The most common condensation polymerisation occurs between monomers containing a carboxylic acid group (–COOH) or an alcohol (–OH) or an amine group (–NH2).
- There is no opening out of double-bonds. The polar bifunctional groups at each end of the monomers react together, such that a small molecule is released (per two monomers which combine) and the monomers join to form a polymer.
- The best way to understand condensation polymerisation is through examples:
2.4 Describe the structure of cellulose and identify it as an example of a condensation polymer found as a major component of biomass
Cellulose as a Condensation Polymer & Major Component of Biomass
- Natural condensation polymer formed through the condensation polymerisation of β-glucose.
- Major component of biomass. Found in wood, paper and cotton, etc.
- Contains 5 x C-C bonds which can be used for the synthesis of polymers and fuels.
- β-1,4-glycosidic linkages are formed between 3000 (up to 10 000) or more glucose monomers to form a flat, straight and rigid cellulose polymer.
- β-glucose monomers are inverted in the chain so that the hydroxy (-OH) groups on C1 and C4 of adjacent molecules are close and can react.
- Alternating glucose-based unit is inverted (180o along the C1 – C4 ‘backbone’ axis relative to the unit adjacent to it) so that the OHs on C1 and C4 can ultimately react. the bulky-CH2OH groups and for
- The –CH2OH groups are on alternate sides and so they don’t interfere with the linear arrangement. This bulky side groups increases stiffness/rigidity.
- The many hydroxyl groups within cellulose molecules –OH hydrogen bond with the hydroxy groups of other cellulose molecules such that the cellulose molecules are held side by side, further enhancing rigidity. The reduced availability of hydroxy groups makes cellulose water-insoluble and relatively resistant to chemical attack.
2.5 Identify that cellulose contains the basic carbon-chain structures needed to build petrochemicals and discuss its potential as a raw material
2.6 …Analyse progress in the recent development and use of a named biopolymer. This analysis should name the specific enzyme(s) used or organism used to synthesise the material and an evaluation of the use or potential use of the polymer produced related to its properties
IUPAC Name polyhydroxybutyrate-hydroxyvalerate
|Background||·||Classified as a polyhydroxyalkanoate (PHA) ‘bacterial plastic’ .|
|Infomation||·||Consists of 3-hydroxybutyric acid and 3-hydroxyvalerate acid monomers|
Bacterium CupriavIdus metalliduran (previously known as Alcaligenes eutrophus. )
Production 1. Grow bacteria in a glucose, nitrogen and valeric acid rich solution for high cell densities.
- Restrict nitrogen from the nutrient supply to stimulate the intracellular accumulation of PHBV.
- Extract by dissolving the PHBV in chloroform, filtering the solid debris, centrifuging, precipitating out the PHA. Dry PHA powder.
|Recent||Developments towards improving economic viability include:|
|Developments||1.||Development of genetically modified E.coli. Scientists have used genetic engineering techniques to locate|
|and transfer the PHA synthesis gene to the familiar bacterium E.coli. This enables: faster growth, better|
|yields, and easier recovery and use of cheap substrates (eg. wastes from sugar milling)|
|2.||Development of genetically modified plants. Using similar methods scientists are able to transfer the PHA|
|synthesis genes into a variety of plants. Eg. GM Arabidopsis thaliana can produce 40% yield plant by dried|
|weight in optimal conditions. Other plant hosts includes aspen trees and cotton plants. This is much cheaper|
|since it is natural process and can be produce PHA without fermentation vats.|
|Despite these significant developments, the cost is still very high relative to petroleum-based plastic, thus further|
|development is required before PHB can be used extensively.|
|Evaluation of||Past uses:|
|Uses in||·||Shampoo bottles, disposable razors ∵ rigid, biodegradable, non-toxic, water-proof. No longer is use due to|
|Relation to||high production costs.|
|·||Sutures for internal surgery ∵ Biodegradable and biocompatible → No allergic reactions and no follow up|
|surgery for removal.|
|·||Replacement for all plastic products eg. biodegradable containers for shampoo, food, milk bottles ∵ Bipol|
|has similar properties to that of polypropylene|
Advantages of its use:
- Biodegradable → less landfill= eco-friendly; sutures → no follow up surgery
- Biocompatible → sutures → no allergic reactions
- Renewable → reduce the dependence on non-renewable sources (fossil fuels) Disadvantage of its use:
- Very expensive → Uneconomical Evaluation:
- Its current use is constrained due to high production costs, but it has the potential to bring large impact particularly to the environment in the future.
3.1 Describe the dehydration of ethanol to ethylene and identify the need for a catalyst in this process and the catalyst used
3.2 Describe the addition of water to ethylene resulting in the production of ethanol and identify the need for a catalyst in this process and the catalyst used
3.3 Describe and account for the many uses of ethanol as a solvent for polar and non-polar substances
- Ethanol can act as a solvent for polar, non-polar and some ionic substances due to the fact that it has both polar and non- polar parts:
- ethyl group – The non-polar section. Attracts non-polar molecules via dispersion forces \Miscible in non-polar liquids (eg. hexane)
- hydroxy group – The main polar section. Very polar O-H bond due to the large differences in electronegativity. Establishes hydrogen bonds/permanent dipole-dipole forces with many solutes containing polar functional groups (eg. glucose, alkanols, acids). Establishes ion-dipole interactions with some ionic compounds\Dissolves polar solutes and ionic compounds. (Note: Ethanol is miscible in water in all proportions due to the strong hydrogen bonding between the two.)
- Uses of ethanol as a solvent:
- Industrial solvent – for varnishes, paints, oils and fatty acids (used industrially due to its relatively high affinity both for water and a range of hydrocarbons)
- Pharmaceutical/medicinal – as alcohol-water mixtures used as antiseptics eg. iodine solutions in ethanol-water mixture (a solvent mixture of ethanol and water is used as non-polar iodine has limited solubility in water)
- Cosmetics – perfumes.
- Food products – colouring and essences
- Domestic cleaning fluid – methylated spirits to wipe away grease
3.4 Outline the use of ethanol as a fuel and explain why it can be called a renewable resource Favourable Characteristics
Favourable Characteristics that Promote Ethanol’s Use as a Fuel/ Fuel Additive
- Combusts more completely and thus more cleanly than current fuels, producing less harmful by-products eg. CO and C: o Complete combustion of ethane – C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g) + 1367kJ Vs
o Complete combustion of octane – 2C8H18(l) + 25O2(g) → 18H2O(g) + 16CO2(g)
These equations demonstrate that ethanol needs less O2 (per mole) for complete combustion than octane fuel
- Renewable and still gives a fairly high energy output per mole → △H= 1367 kJmol-1 10-20% ethanol mixed with current petrol can be used by current motors without the implementation of engine modifications
Ethanol as a renewable resource
- Ethanol is a renewable resource as it can be made from carbohydrates (eg. cellulose, starch, sucrose) that are produced photosynthetically.
- Presence of suitable grain or fruit
- Presence of yeast cultures.
- Exclusion of air (anaerobic conditions)
- Constant temperature of ~37°C.
- Relatively neutral pH
- Fermentation is an exothermic process in which glucose is broken down to ethanol and carbon dioxide by the action of enzymes present in yeast.
- The yeast secretes enzymes, each of which catalyses a specific step in the fermentation reaction sequence.
- Sucrase enzymes in yeast catalyses the breakdown of sucrose into glucose and/or fructose, then zymase enzymes catalyses the breakdown of glucose into ethanol and carbon dioxide:
- Yeast can produce ethanol concentrations of up to 15% ethanol. At these concentrations, yeast cells die and fermentation stops.
- Fractional distillation is used to obtain 95% ethanol (commonly used for industrial or laboratory purposes)
- More complex distillation procedures are needed to obtain close to 100% ethanol due to the strong hydrogen bonding between ethanol and water.
3.7 Define the molar heat of combustion of a compound and calculate the value for ethanol from first-hand data
- The molar heat of combustion of a substance is defined as:
The amount of heat released when 1 mole of a substance undergoes complete combustion (that is, in excess oxygen) to produce carbon dioxide and liquid water only in their standard states at 100 kPa and 25°C
- Note: Heat of combustion is defined as heat released and so a negative sign before a value is NOT required to indicate the exothermic nature of the reaction.
3.8 Assess the potential of ethanol as an alternative fuel and discuss the advantages and disadvantages of its use
Potential of Ethanol as an Alternative Fuel
- 80% of the world’s demand for transportation fuels is petroleum derived. However, as petroleum supplies dwindle, the development of renewable fuel alternatives such as ethanol becomes increasingly more important.
- Ethanol is renewable and easily transportable (liquid form). It also burns cleanly and delivers a fairly high energy output. Thus, ethanol has huge potential as an alternative fuel. The ethanol’s potential is constrained by the high production costs.
- Produced from a renewable source – Can be made from carbs (eg. starch, sucrose) that are produced photosynthetically.
- Complete and clean combustion – Burns more completely and thus more cleanly than current fuels:
C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g) Vs
2C8H18(l) + 25O2(g) → 18H2O(g) + 16CO2(g)
These equn show that ethanol needs less O2 for complete combustion than octane fuel, reducing toxic CO emissions.
- Highly land-inefficient – Vast areas of arable land are required to cultivate cellulose/starch, making less land available for crops/food.
- Costly/energy inefficient – Distillation and isolation of the ethanol, necessary to prevent corrosion of carburettor/fuel injection systems/ fuel lines, is energy-intensive and thus costly
- Engine modifications to existing car engines required if > 10% ethanol is used in fuel. >10% ethanol attracts water which can cause degradation of rubber/plastics parts of fuel systems and corrosion.
- Lower fuel economy – Ethanol has a lower DH (29.7 kJg-1) than octane (47.9 kJg-1). For equal volumes, ethanol releases ~28% less energy than petrol \Inefficient as larger tanks/more frequent fuelling are needed
- Currently, ethanol has potential as an alternative fuel and a future replacement for fossil fuels, particularly for transport. However, further research into developing more efficient methods of ethanol production is required before it can become economically viable.
- Alkanols are a homologous series of compounds that are a subgroup of alcohols. They are characterised by a polar hydroxyl (– OH) functional group attached to a saturated carbon atom.
IUPAC Rules for Naming Alkanols
- Prefixes and suffixes:
|· Steps for naming alkanols:|
|1.||Identify the number of carbons present and determine name of the parent alkane.|
|2.||Remove the ‘-e’ and replace it with the suffix ‘-ol’.|
|3.||Identity the position of the carbon atom bearing –OH group and give its location by the lowest locant possible. Only apply|
|this to chains with three of more carbon atoms. Numbers and letters in IUPAC nomenclature are linked with a hyphen (-).|
|4.||Identify the number of –OH group present in the chain and determine the corresponding suffix. In this case the ‘e’ is NOT|
|dropped from the hydrocarbon name.|
3.10 Process information from secondary sources such as molecular model kits, digital technologies or computer simulations to model the addition of water to ethylene and the dehydration of ethanol
- The use of ball-and-stick models allow for a tactile 3D understanding of the chemical process, thus enhancing understanding of dehydration and hydration processes.
- Both were severely simplified representations of chemical processes, which had many multiple steps and consisted of a series of aqueous sulfuric acid or solid catalysts. The C=C double bonds, depicted by rubber rods, are broken rather opened out which may led to misconceptions.
3.11 Process information from secondary sources to summarise the processes involved in the industrial production of ethanol from sugar cane
Production of Ethanol
- Ethanol can be manufactured in two ways:
- Industrially, ethanol is produced by fermenting sugar in soluble forms such as sucrose and left-over molasses from sugar cane used in sugar milling, or fructose from corn plants. One method for industrial production is as follows:
- Crush and grind sugar-cane into a pulp.
- Hydrolyse with dilute H2SO4, at 100oC for 2 hours to convert cellulose/sucrose into glucose.
- Filter out solid residue of cellulose/lignin from the filtrate of sugars.
- Hydrolyse solid residue with strong acid until it is broken down into sugars.
- Add Ca(OH)2 to the sugar solution to neutralise acid.
- Filter the solution to remove CaSO4 (gypsum) precipitate.
- Ferment the sugar solution, using yeast/GM bacteria, in oxygen-free tank at 37°C to produce 15% ethanol mixture.
- Distill mixture to separate ethanol to obtain high concentration industrial grade ethanol.
- Flowchart of production of ethanol:
3.12 Process information from secondary sources to summarise the use of ethanol as an alternative car fuel, evaluating the success of current usage
- Ethanol is mainly used (mixed with petrol) as a fuel to supplement petrol supplies. Petrol containing 10% ethanol can be used in normal petrol engines without engine modification.
- Ethanol is widely used as a fuel in Brazil – 40% of Brazil’s transport fuel is ethanol. Pros and cons of its use are as follows:
o Brazil is less affected by the current depleting sources than other countries.
- Air quality in big cities improved significantly in the
o The production of ethanol has to be subsidized to make it economically viable for consumption.
- The need of land for crops resulted in deforestation of a significant portion of the Amazon.
- In Australia, ethanol is generally considered an uneconomic proposition – the ethanol industry is not yet profitable as the infrastructure (eg. compatible engines) is limited. Also, Australia lacks the arable land to grow sufficient crops to make enough ethanol to satisfy the liquid fuel demands. With the subsidies and tax concessions in place, there has been an increasing acceptance of ethanol/petrol blends (eg. E10) that have no detrimental effect on vehicles.
- Thus, use of ethanol has proved to be quite successful in Brazil as it is used extensively with positive effects. Howvever, In Australia, the use of ethanol is not as successful, but as petrol prices rise, use of ethanol/petrol blends will become more economically viable.
3.13 Perform a first-hand investigation to determine and compare heats of combustion of at least three liquid alkanols per gram and per mole.
ΔHc = q/m(ethanol) × M
ΔHc = 18.173…× 46.068 [Note: Memorise M(ethanol) = 46.068] ΔHc = 837 kJmol-1 (3s.f)
- The experimental value of the heat of combustion was determined to be ____
- The published value of the heat of combustion of ethanol is 1367 kJ mol-1. So the results of the experiment gave a value which is __% that of the published value. Hence, the accuracy (and reliability) of the experiment very poor due to the fact that much heat was lost during the process.
Ways to Improve Accuracy
- Ways of minimising heat loss/ensuring less heat is lost to surroundings follows:
o Lower the container with the water so that more heat released by the combustion can enter and heat the water. o Use a draught shield around the apparatus.
o Ensure that the inner parts of the clamps are cork-lined (heat insulation).
- Use a conical flask instead of a beaker. The conical flask has a narrow neck and thus water loss through evaporation will be minimized. Above about 30°C a significant amount of water vapour will form and thus a beaker (open) is inappropriate for this experiment. OR Use an Al can rather than a tin can as Al is a good thermal conductor and it has a lower specific heat capacity and less heat absorbed by it so that more can be absorbed by the water.
Heats of Combustion of Alkanols Trends
- All the straight-chained primary alkanols show a consecutive increase by a -CH2 unit.
- methanol, ethanol and 1-propanol are CH3OH, CH3CH2OH and CH3CH2CH2OH respectively. This means that as chain length increases there are more carbon atoms per alkanol molecule to form extra carbon dioxide (O=C=O) during combustion. Hence, the heats of combustion of alkanols should increase successively by a constant amount:
- There is an increase by a -CH2 unit between consecutive alkanols. This means that there are more carbon atoms per alkanol molecule to form extra carbon dioxide (O=C=O) and more hydrogen atoms to form extra water during combustion. Hence, the more bond formations, the more heat energy that is liberated and therefore the greater the heat of combustion. i.e. The heat of combustion is proportional to the CO2 and H2O produced.
- A displacement reaction is an oxidation-reduction reaction involving a transfer of electrons between a metal and a metal ion. This occurs because each metal has a different relative activity.
- For example, zinc metal is immersed in copper sulfate solution:
- Zn is more reactive than Cu so Zn will displace Cu2+ ions from solution. o Zn is preferentially oxidised to produce Zn2+ ions.
- The released electrons are accepted to reduce the Cu2+ ions in solution so that they become Cu(s) as a red-brown deposit form.
4.2 Identify the relationship between displacement of metal ions in solution by other metals to the relative activity of metals
- Displacement reactions can be used to rank metals in order of their strength as reductants/ in order of the relative ease of oxidation.
- The activity series is a list of metals arranged, from left to right, in order of increasing difficulty of losing electrons—that is, in order of decreasing ease of oxidation: a metal on the left loses electrons more easily than a metal to the right of it.
- Active metals displace less active metals from solution.
- The greater the difference in activity between the two metals, the more vigorous the displacement reaction.
4.3 Account for the changes in the oxidation state of species in terms of their loss or gain of electrons
- The oxidation state of an element is a measure of its degree of oxidation or a number given to an atom to indicate (theoretically) the number of electrons it has lost or gained
- Oxidation state/number = the charge on the ion (including the sign) = number that increases on oxidation and decreases on reduction
- Oxidation = increase in oxidation state.
- Reduction = decrease in oxidation state.
- OILRIG = ‘Oxidation is Loss, Reduction Is Gain’
- Changes in the oxidation state of a species can be accounted for in terms of an imagined loss or gain of electrons.
- In NH4, the fact that N has an OxN of –3 does not mean the N atom has a charge of –3. N is just more electronegative than H and can be imagined to attract three electrons more strongly than three of the hydrogens (the fourth H has no electron as it attached to a NH3 molecule as a H+ ion ).
- In NO3, the N is less electronegative than O and can be imagined to attract its five valence shell electrons less strongly than the oxygens do. Thus in NO3, the N has an OxN of +6.
- A galvanic (voltaic/electrochemical) cell is an arrangement of two half cells (one containing a oxidant and the other containing a reductant) that allows a spontaneous redox reaction to take place in such a way that it produces electricity. It usually consists of two electrodes and two electrolytes, connected by a conductive wire (externally) and salt bridge (internally). Oxidation occurs in one half-cell and reduction in the other.
- The electrons that are released at the anode travel through an external circuit to the cathode rather than being transferred through direct contact. The oxidant and reductant are physically separated so that the transferred electrons are directed through an external circuit, creating electricity.
4.5 Outline the construction of galvanic cells and trace the direction of electron flow 4.6 Define the terms anode, cathode, electrode and electrolyte to describe galvanic cells
How a Galvanic Cell Produces Electricity
- Oxidation reaction at the anode (-) liberates electrons out of the metal anode, and flow into the external circuit to the cathode.
- The reduction reaction at the cathode (+) consumes these electrons.
- As the anodic metal is slowly oxidised, and more anions build-up, the anolyte solution accumulates in positive charge (eg. more Zn2+ than SO42-). Similarly, as the cations are reduced, the catholyte solution builds in negative charge (eg. more SO42-than Cu2+). To maintain electrical neutrality, ions migrate into the solutions through the connecting salt bridge.
- The flow of electrons acts as a source of electric current/voltage
3.14 Gather and present information on the structure and chemistry of a dry cell and evaluate it in comparison to a silver-oxide button cell in terms of: - Chemistry, cost and practicality, - impact on society, - environmental impact
4.7 Solve problems and analyse information to calculate the potential E° requirement of named electrochemical processes using tables of standard potentials and half-equations
5.1 Distinguish between stable and radioactive isotopes and describe the conditions under which a nucleus is unstable
- Radioactivity is the spontaneous emission of radiation from certain atoms which have an unstable nucleus.
- Stable Isotopes are isotopes of an element that do not emit radiation , radioactive isotopes are isotopes of an element whose nucleus emit radiation (afterwards becoming stable)
- For some elements (e.g. carbon), some of their isotopes are stable (such as carbon-12), and others are radioactive (such as carbon-14).
Atomic number larger than 83 – All atoms (including ALL their isotopes) with more than atomic number 83 (ie. Z > 83) are radioactive.
- Proton-neutron ratio – Atoms with a neutron to proton ratio that is too large or too small are radioactive. Eg. Lighter elements (Z < 20) have a n:p of 1:1 and heavier elements have a n:p of ~1.5.
- Metastable nucleus – Eg. Technicium-99m
- Transuranic elements are elements with atomic numbers greater than 92 (ie. greater then uranium, that is, Z > 92)
- All transuranic elements are artificially produced.
Production of Transuranic Elements
- Neutron Bombardment (in nuclear reactors):
- In these nuclear reactions, the fission chain-reaction (eg. uranium-235) produces large amounts of neutrons. When atoms are placed inside the reactor, they are bombarded by these neutrons. Occasionally the atom absorbs one of
these neutrons creating a isotope of the bombarded atom; however, it is unstable, and undergoes beta decay. Hence the atomic number increases (ie. proton number increases), and a transuranic element can be created.
- g. Uranium-238 is not fissile (cannot undergo the nuclear chain-reaction) and undergoes the following reaction:
- Fusion Reactions (in particle accelerators) [eg. cyclotrons or linear particle accelerators]:
- The production of larger transuranic elements is achieved by colliding heavy nuclei with high-speed positive nuclei particles like helium or carbon nuclei’s (Note: every nuclei has no electrons orbiting it, hence its positive). The positive particles need to be at very high speeds to overcome the positive repulsive force of the heavy nuclei and fuse with them.Particle accelerators are used to bring these particles to the high speeds required. o E.g. Uranium-238 is fused with a carbon particle (ie. nuclei) to form californium-246:
- Note: the neutrons present, are ejected from uranium and carbon, they don’t then react with californium such that it beta decays.
- Element 110 was discovered in 2001 by a team from Darmstadt in Germany. This was produced by the fusion of Pb-208 and Ni-62, which formed 269-Ds and a neutron:
- This is formed by using a particle acceleration to accelerate the lighter Ni-62 towards a target made of the isotope Pb-208, forming Darmstadium which quickly decays.
- Isolation of an observable quantity has never been achieved, and may well never be. This is because atoms of the element decompose through the emission of alpha particles with a half-life of only about 270 μs.
- Also known as “eka-polonium”, element 116 was synthesised in December, 2000, by the Joint Institute for Nuclear Research
(Dubna, Russia). It was produced through the fusion of curium-248 and calcium-48. The atom decayed 48 milliseconds later.
- Many commercial radioisotopes are produced by neutron bombardment within nuclear reactors, at the Lucas Heights nuclear reactor, Sydney to produce a range of neutron-rich isotopes:Technitium-99m (medical) is produced by neutron bombardment of molybdenum-98
- Technitium-99m (medical) is produced by neutron bombardment of molybdenum-98
- Cobalt-60 (industrial/medical) is produced by neutron bombardment of the stable cobalt-59
- Other isotopes are produced by fusion reactions by particle accelerators, such as the National Medical Cyclotron, near the Royal Prince Alfred hospital. Particle accelerators accelerate nuclei to incredible speeds, and which are then collided with heavy nuclei. This produces neutron-deficient radioisotopes. Radioisotopes produced include:
- Iodine-131 (used to diagnose thyroid disorders)
- Carbon-11, nitrogen-13, oxygen-15 (all used in PET scans)
- Detects ionising particles/radiation
- The a- or b-radiation enters the tube, collides with a gas molecule (eg. argon), ionises it into cations and electrons. Electrons move to anode, cations move to cathode to produce a current.
- The current creates a voltage pulse that amplified and counted. Each pulse
corresponds to one ionising radiation entering the tube.
- Photographic film is a sheet of plastic coated with silver halide salts
- These salts are sensitive to EMR , and darken when they are exposed to radiation.
- Some substances give off light when they are struck by high-energy radiation
- A photo-receptor cell senses these flashes of light that occur, and from this measures the number of decay events that are occurring.