CHEMISTRY: RADIOACTIVITY
About radioactivity- It is the process by which an unstable atomic nucleus spontaneously decays (loses energy) by emitting ionizing particles and radiation
- This decay results in the atom of one type (parent nuclide) transforming into an atom of a different type (daughter nuclide)
- Eg: Carbon-14 emits radiation and transforms into nitrogen-14
- The SI unit of radioactivity is Becquerel (Bq). Another commonly used unit is the Curie (Ci)
- Radioactivity of a material is quantified by its half life. This is the time taken for a given amount of a radioactive material to decay to half its initial value
- Radiation can be measured using scintillation counters and Geiger counters
History of radioactivity research
- Radioactivity was first discovered by French scientist Henri Becquerel in 1896
- Research in radioactivity of uranium led Marie Curie to isolate a new element Polonium and to separate Radium from Barium
- The dangers of radioactivity was discovered by Nikola Tesla in 1896, when he intentionally subjected his fingers to X-rays
- Henri Joseph Muller was awarded the Nobel Prize in Physiology or Medicine in 1946 for his discovery (in 1927) of the harmful genetic effects of radiation
Transmutation of elements
- Isotopes: they are atoms of an element with the same atomic number but different mass number (eg uranium-238 and uranium-235)
- Isobars: elements with same mass number but different atomic number. Usually occurs when a radioactive nucleus loses a beta particle (eg. Thorium-234 and palladium-234)
- Isotones: radioactive nuclei that contain the same number of neutrons (eg. Radium-226 and Actium-227)
- Isomers: are different excitation states of nuclei. The higher-energy (unstable) element undergoes isomeric transition to form the less energetic variant without change in atomic or mass number
Types of radioactive decay
Alpha rays can be stopped by a sheet of paper, beta rays by aluminium shielding, while gamma rays can only be reduced by a thick layer of lead
- Radioactive radiation can be split into three types of beams
- Alpha rays: they are helium particles that carry a positive charge. They have low energy and can be stopped by a sheet of paper
- Beta rays: they are streams of electrons and carry negative charge. They have higher energy than alpha rays
- Gamma rays: they are high energy rays (like X-rays) that carry no electrical charge
Radioactivity and the Big Bang theory
- According to the Big Bang theory stable isotopes of the lightest elements (H, He, Li, Be, B) were formed immediately after the Big Bang
- Radioactive (unstable) isotopes of these light elements have long since decayed, and isotopes of elements heavier than boron were not produce at all in the Big Bang
- Thus, the radioactive materials currently in the universe were formed later and are relatively young compared to the age of the universe
- These radioactive nuclei were formed in nucleosynthesis in stars and during interactions between stable isotopes and energetic particles
- For instance, carbon-14 is constantly produced in the earth’s upper atmosphere due to interactions between cosmic rays and nitrogen
Applications of radioactivity
- Radioisotopic labeling: used to track the passage of a chemical through the human body. Some common radio isotopes used for labeling are
- Tritium: used to label proteins, nucleic acids
- Sodium-22 and Sodium-36: ion transporters
- Sulphur-35: proteins and nucleic acids
- Phosporous-32 and Phosphorous-33: nucleotides (like DNA)
- Iodine-125: thyroxine
- Carbon-14 is not used for radioactive labeling due to its long half life (5730 years)
- Random number generators: based on the premise that radioactive decay is truly random
- Radiometric dating: used to date materials based on a comparison between observed abundance of radioactive isotopes and its decay products, using known decay rates. The most common methods of radiometric dating are
- Carbon dating: when organic matter grows, it traps carbon-14. The age of the organic matter can be estimated by measuring the amount carbon-14 remaining in the body. Used for dating material up to 60,000 years old
- Potassium-argon dating: used in geochronology and archeology, especially for dating volcanic material. Used for samples older than a few thousand years
- Uranium-lead: one of the oldest and most refined radiometric dating techniques. Used in geochronology to estimate material from 1 million to 4.5 billion years old. A variant, the lead-lead dating scheme was used by American scientist Clair Cameron Patterson to estimate the age of the earth (4.55 billion years) in 1953
Radioactive therapy
- Used for palliative and therapeutic treatment
- Common applications include treatment of thyroid eye disease, heterotopic ossification, trigeminal neuralgia
- In low doses, it is used for cancer treatment. However, in large doses, it can cause cancer
- Total body irradiation is used to prepare the body to receive a bone marrow transplant
Radiation poisoning
- It is a form of damage to organ tissue due to excessive exposure to ionizing radiation
- Caused by exposure to large doses of radiation in short periods of time, or by exposure to small doses over long periods
- Increases the probability of contracting other diseases like cancers, tumours and genetic damage
- Common symptoms are nausea and vomiting
- Common occurrances of radiation poisoning include nuclear warfare, nuclear reactor accidents, spaceflight (exposure to cosmic rays), ingestion and inhalation of radioactive compounds (such as strontium in cow’s milk)
- In Nov 2006, Russian dissident died due to suspected deliberate ingestion of Polonium-210
CHEMISTRY: ELECTROLYTES
Electrolytes in the human body
- Electrolytes are required in the body to maintain balance between intracellular and extracellular liquids. In particular, it is important to maintain the osmotic gradient between inside and outside.
- Electrolyte balance is maintained by oral and intravenous intake
- Kidneys flush out excess electrolytes
- Dehydration and overhydration are caused by electrolyte imbalance
- Hormones that maintain electrolyte balance are antidiuretic hormone, aldosterone and parathyroid hormone
- The most common electrolyte in the body is salt (sodium chloride)
- In Nov 2006, Russian dissident died due to suspected deliberate ingestion of Polonium-210
- Maintain blood pH
- Muscle and neuron activation
- Hydration of the body
- Sports drinks
- Batteries
- Fuel cells
- Electroplating
- Capacitors
- Sports drinks replenish the body’s water and electrolyte levels after dehydration caused by exercise, vomiting, diarrhea etc.
- They are made of electrolytes containing sodium and potassium salts
- Examples of sports drinks: Glucon-D, Gatorade etc
- Simplest electrolyte drink that can be made at home is water + sugar + salt
| Battery | Electrode | Electrolyte | Other notes |
| Alkaline | Zinc, Manganese oxide | Potassium Hydroxide | |
| Daniell cell | Copper, Zinc | Copper sulphate, zinc sulphate | |
| Leclanche cell | Zinc, carbon | Ammonium chloride | Precursor of modern dry cell |
| Voltaic pile | Copper, zinc | Brine | First electric battery, invented in 1880 |
| Zinc carbon | Zinc, carbon, manganese dioxide | Zinc chloride, ammonium chloride | Most common battery |
| Zinc chloride | Same as above | Zinc chloride | Improvement on zinc carbon battery |
| Lead-acid | Lead, lead dioxide | Sulphuric acid | Oldest rechargeable battery Used in vehicles as they provide high surge currents |
| Lithium-ion | Graphite, Lithium Cobalt oxide | Non-aqueous lithium salts | Rechargable Slow self-discharge, high energy to weight ratio |
| Nickel Cadmium | Nickel oxide hydroxide, cadmium | Rechargable Last longer, more stable than lithium ion | |
| Fuel cell | Hydrogen (fuel), oxygen (oxidant) | Polymer membrane Aqueous alkaline solution | Consumes reactant from an external source High energy efficiency and high reliability No moving parts Used in space shuttles, submarines |
| Electrolyte | Uses | Other notes |
| Sodium chloride | Primary component of extracellular fluid Food preservative | |
| Sodium hydroxide (caustic soda) | Manufacture of paper, soaps, detergents, drain cleaners Purification of drinking water | |
| Silver nitrate | Photographic films Water disinfection (esp. on space shuttles) | |
| Hydrochloric acid | Manufacture of PVC, household cleaners Food additives (like gelatin) Leather processing | Found naturally in gastric acid |
| Sulphuric acid | Lead-acid batteries Ore processing Fertilizer manufacture | Soluble in water at all concentrations One of the largest products of chemical industry |
| Nitric acid | Determining metal traces in solutions Wood finishing | Colourless when pure, yellows with age Highly corrosive |
| Acetic acid | Manufacture of soft drink bottles Photographic films Synthetic fibres and fabrics | Dilute acetic acid is called vinegar |
| Ammonium hydroxide (aqueous ammonia) | Cleaning agent | |
| Calcium hydroxide (slaked lime or pickling lime) | Sewage treatment Whitewash, plaster, mortar Hair relaxers | Natural mineral form is called portlandite (rare mineral occurring in volcanic rocks) |
-
CHEMISTRY
CERTAIN COMMON SUBSTANCES
- Hydrogen
- Has same atomic number and atomic weight: 1
- Most abundant element in the universe
- Is the lightest element
- isotopes are Protium, Deutrium, Tritium
- Heavy water: water which has Deutirum instead of Hydrogen. Obtained by electrolysis of water. Used as moderator in nuclear reactors
- Used to prepare vanaspati by hydrogenation of vegetable oil
- Oxygen
- Most abundant element on earth’s crust (50% of all elements)
- Used for artificial respiration, and along with Nitrogen as an anesthetic
- Water
- About 70% of earth’s surface and 65% of body weight
- Hardness of water due to dissolved salts of Calcium and Magnesium
- Temporary hardness due to bicarbonates of Ca and Mg. Can be removed by boiling
- Permanent hardness due to chlorides and sulphates of Ca and Mg. Can not be removed by boiling
- Rain water is the purest form of water
- River water is hard water
- Spring water purer than river water
- Sea water is hard water. Contains Sodium Chloride in addition to salts of Ca and Mg
- Mineral water: spring water with minerals and having medicinal value
- Nitrogen
- Most abundant in atmosphere (78%)
- Occurs in animals and plants in the form of protein
- Used to manufacture fertilizers and explosives
- Liquid nitrogen used in refrigeration
- Phosphorus
- Found in bones, brain and urine
- Glows in dark
- Red phosphorus used to make matches
- White phosphorus used in smoke screens
- Carbon
- Second most abundant element in human body after Oxygen
- Occurs in free state as diamond, coal and graphite
- Diamond: purest form of carbon, hardest naturally occurring substance
- Graphite: only non-metal to act as a good conductor of electricity. Used to make lead pencils and lubricants
- Coal: formed by bacterial decomposition of plant material. Peat coal has lowest carbon content (60%), anthracite has highest (90%)
- Carbon gas: not a gas. Obtained by heating powdered coal and tar in absence of air. Good conductor of electricity
- Coke: obtained by heating coal in absence of air. Used as household fuel and in steel industry
- Wood charcoal: obtained by burning wood. Used to make gas masks, acts as bleaching agent
- Bone charcoal: obtained by destructive distillation of bones. Used as a decolouring agent in sugar industry
- Lamp Black: obtained by burning vegetable oil. Used to make printer’s ink and boot polish
- Sodium
- Does not occur in free state
- Highly reactive, always kept under kerosene
- Used to make sodium vapour lamps
- Removes traces of water in alchohol manufacturing
- Silver
- Best conductor of electricity
- Used to make jewellery, mirrors and hair dyes
- Gold
- Highly inert, does not react with water, air, alkalies or acids. Dissolves in aqua regia. Used to make electron microscope
- Aluminium
- Third most abundant on earth’s crust (8%)
- Used to make cooking utensils, transmission wires, paint
- Alloys Duralumin and Magnalumin used in aircraft building
| Halogen | Occurrence | Uses |
| | | |
| Fluorine | Gas Found in soil, sea water Found in tooth enamel |
|
| | | |
| Chlorine | Gas Found in common salt |
|
| | | |
| Bromine | Liquid |
|
| | | |
| Iodine | Solid Found in sea water, sea weeds Found in thyroid gland |
|
| Compound | Uses |
| | |
| Sodium peroxide |
|
| | |
| Sodium hydroxide (caustic soda) |
|
| | |
| Sodium carbonate |
|
| | |
| Sodium bicarbonate (baking soda) |
|
| | |
| Sodium chloride (common salt) |
|
| | |
| Sodium nitrate (Chile saltpetre) |
|
| | |
| Sodium sulphate (Glauber’s salt) |
|
| | |
| Sodium thiosulphate (hypo) |
|
| Compound | Uses |
| | |
| Potassium hydroxide (caustic potash) |
|
| | |
| Potassium bromide |
|
| | |
| Potassium nitrite (nitre) |
|
| | |
| Potassium chlorate |
|
| | |
| Potassium carbonate (potash) |
|
| Alloy | Components | Uses |
| | | |
| Bell metal | Copper, Tin |
|
| | | |
| Brass | Copper, Zinc |
|
| | | |
| Bronze | Copper, Tin, Zinc |
|
| | | |
| German silver | Copper, Zinc, Nickel |
|
| | | |
| Gun metal | Copper, Tin, Zinc |
|
General Studies :: Chemistry #1
Distribution of elements on the surface of the earth
| Element | Distribution | | Element | Distribution |
| | | | | |
| Oxygen | 49.85% | | Silicon | 26.03% |
| | | | | |
| Aluminium | 7.28% | | Calcium | 3.18% |
| | | | | |
| Sodium | 2.33% | | Potassium | 2.23% |
| | | | | |
| Magnesium | 2.11% | | Hydrogen | 0.97% |
| | | | | |
| Titanium | 0.41% | | Chlorine | 0.20% |
| | | | | |
| Carbon | 0.19% | | Others | 1.00% |
Metals and their ores
| Substance | Ore | | Substance | Ore |
| | | | | |
| Calcium | Limestone, marble, chalk | | Mercury | Cinnabar |
| | | | | |
| Copper | Copper pyrites, Cuprite | | Potassium | Carnelite, Saltpetre |
| | | | | |
| Cement | Limestone and clay | | Sodium | Rock salt, Cryolite |
| | | | | |
| Glass | Silica and lime stone | | Thorium | Monozite |
| | | | | |
| Iodine | Sea weeds | | Titanium | Rutile, limenite |
| | | | | |
| Iron | Hematite, Magnatite, Iron pyrites | | Uranium | Pitchblende |
| | | | | |
| Gold | Aurite | | Silver | Argentite |
Metals and their alloys
| | Alloy | Component |
| | | |
| | Brass | Copper, Zinc |
| | | |
| | Bronze | Copper, Tin, Zinc |
| | | |
| | Gun metal | Copper, Tin, Zinc |
| | | |
| | Duralmin | Aluminium, Copper, Magnesium, Manganese |
| | | |
| | Solder | Aluminium, Lead, Tin |
| | | |
| | Pewter | Lead, Tin |
No comments:
Post a Comment