Concise Chemistry: Atomic Mass, Radiation, Water & Polymers
Atomic Structure and Radiation
- The relative atomic mass, Ar, or atomic mass, is the mass of an atom measured by comparison with the carbon atom -12.
- Alpha Particles: consist of two protons and two neutrons, i.e., are nuclei of helium atoms. When a radioactive nucleus emits an alpha particle, it is transformed into another with mass number A-4 and atomic number Z-2.
- Beta particles: are very fast electrons. They result from the disintegration of neutrons into a proton and an electron. When emitted, the mass number does not change, but the atomic number increases by one unit.
- Gamma radiation: is high-energy radiation, part of the electromagnetic spectrum. Its emission does not alter the atomic number or mass number because it is a nuclear energy adjustment.
One way to characterize a radioactive isotope is the half-life, which is the time required for half of the nuclei present in a sample of radioactive isotopes to disintegrate.
- Nuclear energy follows the disintegration of the nuclei of certain atoms.
- Nuclear fission is the breaking of a heavy atomic nucleus into two fragments of similar mass. It releases a lot of energy, and neutrons are the projectiles that are used most frequently to break atomic nuclei.
Properties of Water
- Water remains liquid. Other similar substances are transformed into gases.
- The density of water increases abnormally by raising the temperature to 4 º C.
- Ice floats on water.
- It’s an excellent storage heater and has resistance to increase or decrease its temperature.
- It is able to keep insects floating on the surface or objects much denser than it.
- It is broken down into its elements at 1500 º C.
- It is the best solvent and the best carrier of substances.
- In the liquid state, some molecules are linked together and form clusters. The holes are occupied by single molecules.
- In the solid state, the molecules are tightly bound and adopt hexagonal shapes. Gaps are not occupied by single molecules and have less density.
Organic Compounds
- Alkanes: methane, home heating, combined cycle power plants.
- Alkenes: Ethene or ethylene for the production of organic polymers.
- Alkynes: ethyne or acetylene, colorless gas used for lighting a bright flame.
- Cellulose: the most abundant organic substance on our planet. It is a supporting material. Chains are very long and constitute raw material in many industries, including paper manufacturing.
- Natural rubber: a hydrocarbon polymer of isoprene. Its molecules are long and flexible and tend to curl. These properties are caused by the presence of a double bond in the macromolecule. By extension, the chains are stretched and placed almost parallel to each other, but under constant stress, they tend to curl and return, so it is elastic.
Plastics and Elastomers
- Thermoset Plastics: Once they have hardened, they do not soften when reheated. Their molecules consist of long chains linked together tightly. These bonds cannot be broken when the plastic is heated, so it always keeps its shape. Examples: Bakelite, melamine resins, and epoxy resins.
- Thermoplastics: Soften when heated, but their form is stabilized when cooled again. Molecules consist of long chains linked by weak bonds. These links are broken when the plastic is heated, so it can acquire a different appearance and maintain its new shape when cooled. Examples: Polyethylene, polypropene, polystyrene, PVC.
- Elastomers: More elastic than plastic and have low hardness. Their molecules consist of long chains attached laterally and folded in on themselves. Also known as synthetic rubbers. Examples: Rubber & Neoprene.