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Year 9 Chemistry

Year 9 Chemistry. Models of the atom. 400BC Democritus Atomic Model Matter is made up of indivisible particles Limitation: No scientific evidence to support this theory. Models of the atom. 1803 Dalton Billiard Ball Experimental evidence of conservation of mass

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Year 9 Chemistry

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  1. Year 9 Chemistry

  2. Models of the atom 400BCDemocritus Atomic Model Matter is made up of indivisible particles Limitation: No scientific evidence to support this theory

  3. Models of the atom 1803Dalton Billiard Ball Experimental evidence of conservation of mass All atoms of a given element are identical, but different to the atoms of another element. Compounds form from atoms of more than one element and only whole atoms can combine. In a chemical reaction, atoms can be separated or combined but never destroyed Limitation: No mention of sub-atomic particles

  4. Models of the atom 1898Thompson Plum pudding Evidence of two types of sub-atomic particles. Negatively charged electrons (plums) were embedded in a positively charged pudding Limitation: Arrangement of sub-atomic particles incorrect

  5. Models of the atom 1910Rutherford Nuclear Positive protons concentrated in small nucleus. Mass concentrated in nucleus. Atom consists mainly of empty space Volume due to motion of negative electrons. Limitation: Could not explain how the electrons were arranged or how they moved

  6. Models of the atom 1910Rutherford Nuclear Positive protons concentrated in small nucleus. Mass concentrated in nucleus.

  7. Models of the atom 1913Bohr Planetary Electrons found in fixed orbits. Electrons with lower energy found in orbits closer to nucleus. Limitation:Could not explain small energy differences between electrons in the same energy level

  8. Models of the atom 1932Chadwick Discovered neutrons – important in accounting for mass of nucleus, and unstable atoms

  9. THE STRUCTURE OF THE ATOM The atom consists of a central nucleus containing protons and neutrons. Orbiting around the nucleus are electrons.

  10. THE STRUCTURE OF THE ATOM Protons These are positively charged particles found in the nucleus They have a mass of 1,67 x 1027 kg. Since this is such a small number, a new unit of measurement is used; the Atomic Mass Unit (u). One proton has a mass of 1u. Atoms of the same element will always have the same number of protons and an element can be identified by the number of protons found in its atoms

  11. THE STRUCTURE OF THE ATOM Neutrons These are neutral particles found in the nucleus of the atom They have the same mass as the proton ie: one neutron has a mass of 1u The number of neutrons can vary from one atom to the next within the same element (see Isotopes)

  12. THE STRUCTURE OF THE ATOM Electrons These are negatively charged particles found orbiting the nucleus They are extremely tiny, with a mass of 1/1840u They can be added to or removed from atoms to form ions They make up the volume of the atom in a neutral atom, there are the same number of electrons as protons

  13. THE STRUCTURE OF THE ATOM Atomic Number (Z) is the number of protons found in the nucleus. Atomic Mass Number (A) is the total number of (protons + neutrons) found in the nucleus (Therefore the number of neutrons can be found by subtracting the Atomic Number from the Atomic Mass)

  14. Molecules are particles that can move independently of each other.

  15. Lattices are 3 dimensional arrangements of atoms or ions Above: NaCl, common salt Left: SiO2 , sand

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  18. HALF LIFE What is Half-life? 1. Half-life is the time taken for half of the radioactive nuclei to decay 2. Half-life is the time taken for the count rate to fall to half its original reading.

  19. HALF LIFE What is Half-life? An Explanation of Half-life. A radioactive material will have some nuclei that are stable and some that are unstable. The stable nuclei don’t change, that is what stable means. In the picture below, the unstable nuclei (shown as brown balls) will change into stable nuclei (shown as purple balls) and emit radioactivity.

  20. HALF LIFE What is Half-life? An Explanation of Half-life. Half-life is a measure of the time taken for
the unstable nuclei to change into stable nuclei. Different substances do this at different rates.

  21. HALF LIFE Some do it very quickly and half of the unstable nuclei decay
in less than one second. For example, lithium-8 has a half-life of only 0·85 seconds. Some do it very slowly and half of the unstable nuclei takebillions of years to decay.
For example, uranium-238 has a half-life of 4·51 billion years.

  22. HALF LIFE

  23. ‘Dating’ Methods Carbon 14 dating – relies on the half life of C-14, 5730 years. Useful for dating once living relics, less than 50000 years old. Useful for archeologists and anthropologists. C-14 is produced in the atmosphere when cosmic rays strike N-14 atoms. All living things take in C-14 as they live, the level stays relatively constant, When the organism dies, no new C-14 is taken in, and the C-14 remaining in its body decays. It is like a chemical ‘hourglass’.

  24. ‘Dating’ Methods Carbon 14 dating – relies on the half life of C-14, 5730 years. Useful for dating once living relics, less than 50000 years old. Useful for archeologists and anthropologists. C-14 is produced in the atmosphere when cosmic rays strike N-14 atoms. All living things take in C-14 as they live, the level stays relatively constant, When the organism dies, no new C-14 is taken in, and the C-14 remaining in its body decays. It is like a chemical ‘hourglass’.

  25. ‘Dating’ Methods Below is a list of signs and symptoms likely to occur when a human is exposed to acute radiation (within one day), in mSv: 0 to 250 mSv - no damage 250 to 1,000 mSv. Some individuals may lose their appetites, experience nausea, and have some damage to the spleen, bone marrow and lymph nodes. 1000 to 3000 mSv - nausea is mild to severe, no appetite, considerably higher susceptibility to infections. Injury to the following will be more severe - spleen, lymph node and bone marrow. The patient will most likely recover, but this is not guaranteed. 3,000 to 6,000 mSv - nausea much more severe, loss of appetite, serious risk of infections, diarrhea, skin peels, sterility. If left untreated the person will die. There will also be hemorrhaging. 6,000 to 10,000 mSv - Same symptoms as above. Central nervous system becomes severely damaged. The person is not expected to survive. 10,000+ mSv - Incapacitation. Death. Those who do survive higher radiation doses have a considerably higher risk of developing some cancers, such as lung cancer, thyroid cancer, breast cancer, leukemia, and cancer of several organs.

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