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Year 10 Chemistry Summary Notes

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Summary Notes from the Year 10 Syllabus Chemistry Section
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  Chemistry Summary Notes Recall the structure of the atomic nucleus. (1) Atoms are composed of sub- atomic particles. The three main particles are: -   Protons: positively charged (+1); in the nucleus; have an atomic mass of 1 unit. -    Neutrons: no charge; in the nucleus; have an atomic mass of 1 unit. -   Electrons: negatively charged (-1); orbit nucleus; are about 1/2000 th  the mass of proton or neutron. -   The nucleus is very small and dense. How the electrons are arranged for the first twenty elements. -   The electrons are arranged in orbits at different energy levels around the nucleus. -   The inner or first orbit can have up to two electrons. -   The second and third orbits can have up to eight electrons. Atomic number  –   the number of protons in an atom. This identified the atom. Every atom has an equal number of protons and neutrons Mass number  –   the number of protons + the number of neutrons in the nucleus of an atom  Define the terms “isotope”, “radioisotope” and “nuclear radiation”.  (2) Isotope  –   Isotopes of an element all have the same number of protons, but a different number of neutrons. Radioisotope  –   Unstable isotopes that decay or break up, giving off high-energy radiations (alpha,  beta and gamma radiation) and forming different atoms.  Nuclear radiation  –   the energy and the particles that are released from the nucleus in its break-up  Define the terms “radioactivity”, “alpha particle”, “beta particle”, “gamma radiation” and “half  -  life”.  (3) Half-life  –    the length of time required for half of the isotope’s atoms to dec ay. This length is different for each radioisotope. Radioactive decay  –   the process of changing from one element to another while emitting radiation Alpha Particles ( α) -   Small, heavy and positively charged particle make of 2 protons and 2 neutrons stuck together -   An alpha particle is a Helium ion  242 He  -   Do not travel fast, when moving through air they hit into anything near them and do a lot of damage -   Lose energy very quickly -    Not able to penetrate a piece of paper Beta Particles ( β)  -   Very small, light and fast moving negatively charged particles -   Electrons which have come from the nucleus -   Damage they do is more spread out  -   They will penetrate thin aluminium foil or a piece of paper Gamma rays ( γ) -   Similar to x-rays, not particles but electromagnetic waves -   They have no mass or charge and travel at the speed of light -   Go through most things easily, able to be stopped by a metre of concrete or 10cm of lead Use the correct notation to denote isotopes (nuclear symbol).(4) FOR EXAMPLE: URANIUM   235   mass number  U 92   atomic number   Describe, with examples, uses of radioisotopes in society. (5) Industrial Uses Food preservation  –   food in sealed containers can be preserved by exposing it to gamma radiation. The radiation kills the micro-organisms in the food and keeps it from spoiling. Other uses -   Examining faults in planes -    Nuclear weaponry -   Smoke detectors Medical Uses Treating cancer  –   radiotherapy is the use of radioisotopes, or other radiation such as X-rays, to kill cancer cells or prevent them from multiplying. It can be targeted in a small area so that the surrounding tissue is not damaged. There are two methods to this, internally, when the radioactive  material is placed inside the body, or externally, where the radioactive material is shot into the body from outside it. Diagnostic medicine  –   radioactive substances may be inserted into the body to detect or identify the cause of disease. The radiation produced by the substance while it is in the part of the body under investigation is measured to diagnose the problem. Other uses: -   Sterilising medical equipment -    Nuclear medicine -   Gamma rays emitting radioactive tracers are swallowed by patients to diagnose problems in the  body Describe the benefits and problems in medical and industrial uses of radioisotopes. (6) Advantages: -   Used to diagnose and treat cancer -   Can be used to detect faults in machinery without taking the machinery apart e.g. jet engines -   Can be used to detect the thickness of materials -   Can be used to work out the absolute age of rocks (and thus, the age of the Earth). Disadvantages: -   Can kill good cells in the process of detecting or treating illnesses -   Radioisotopes used in industry, medicine or scientific research can harm the users, so they need to be monitored for their exposure levels -   In the process of killing cancer cells, healthy cells are also killed leading to short-term illness and short effects -   Food irritation causes bacteria as well as vitamins to be destroyed and new chemicals to be created within food Radiation Sickness -   Very high levels of nuclear radiation (such as that given off in a nuclear bomb) can cause radiation sickness -   Many of the organs inn the body can be affected, making the person very sick, affect the reproductive organs and possibly lead to death. Cancer -    Nuclear radiation can alter the DNA in cells, causing mutations and possibly alter them in a way that can cause them to become cancerous. -   Sometimes the cancer doesn’t develop until many years after exposure to radiation. Recall the problems with fossil fuels. (7) Environmental Dangers i.e. pollution  –   when fossil fuels are burnt they release carbon dioxide, a greenhouse gas which is a main contributor to global warming Acid rain  –   Sulphur oxide, another greenhouse gas, is released and absorbed by clouds. When these clouds rain, the rain becomes acidic, contributing to the destruction of buildings, crops and land formations. Affecting human health  –   the ozone layer id depleting due to excessive fossil fuel burning, causing harmful UV rays to seep into the earth’s troposphere and atmosphere, causing life threatenin g diseases such as skin cancer  Impacts on aquatic life  –   oil spills are more frequent with the increased use of fossil fuels. Crude oil mixed into the ocean causes serious health effects to aquatic life. Coal mining  –   Coal mining destroys vast amounts of land, resulting in an ecological imbalance disturbing wildlife and the ecosystem. Rising prices and non-renewable  –   due to their limited availability, the prices for fossil fuels are  beginning to skyrocket, creating political unrest amongst its biggest users as well as major problems if it begins widely unavailable. Discuss the advantages and disadvantages of using nuclear power stations. (8) Advantages -   Produces much less carbon emission than fossil fuels -   Only around 3 percent of nuclear waste is classified as high level waste -   The volum e of high level waste produced per person for a lifetime’s worth of energy is tiny  -   The fission products are dangerous for a certain time, around 300 years -   The 97% remaining waste shouldn’t be regarded as waste, but rather be reused and recycled  Disadvantages -   Britain already has enough waste to fill Albert hall 5 and a half times -   High level waste is extremely dangerous and must be safely stored for thousands of year  –   a terrible legacy for future generations -   97% of high level waste takes thousands of years to decay State and explain the law of conservation of matter. (9) The law and conservation of matter states that in any given system that is closed to the transfer of matter, the amount of matter in the system stays constant. The law of conversation of matter says that in chemical reactions, the total mass of the products must equal the total mass of the reactants. Recall acids, bases and salts. (10) Acids and bases neutralise  one another: ACID + BASE SALT + WATER The products (i.e. the salt and water) are neutral (i.e. they have a pH of 7). A salt is defined as the product formed from the neutralisation reaction of acids and bases. Salts are composed of a metal and a non-metal.  Neutralisation Reactions hydrochloric acid + sodium hydroxide   sodium chloride (table salt) + water Salts:    All salts have a crystalline structure and high boiling points and most dissolve in water.    A salt is an example of what is known as an ionic compound.    The name of a salt contains at least two words, which identify the ions that make it up (e.g. sodium chloride contains sodium and chloride ions).    Salts are composed of metals and non- metals or groups of non- metals.
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