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Science Summary I Exam, II Trimester 1. Describe the structure of atoms. All matter is made up of atoms. An Atom is the smallest particle into which an element can be divided and still be the same substance. Atoms of the same element are identical, and atoms from different elements are different. The atom itself has sub-atomic particles with different electrical charge. These are: Protons (P+): Positively charged sub-particles that are located in the nucleus (central part of the atom). Electrons: (e-): Negatively charged sub-particles that move around the nucleus in energy levels. Electrons are found likely in the electron clouds. Neutrons: (n): Sub-particles located in the nucleus, with no electrical charge. The n and the P+ determine the atom´s mass. The e- determines the volume of the atom. 2. Define these terms: (# = number) Atomic #: Number of P+ Mass #: Number of n plus number of P+ Atomic mass: Isotope X Abundance / 100 Example: Boron-10 has an abundance of 20%, what is the atomic mass? 10 X 20 / 100 = 2 a.m.u. Isotopes: are atoms that have the same # of protons but different number of neutrons. Ion: an atom that has different number of electrons. Anion: ion that gains electrons, so the atom gains a negative charge. Cation: ion that loses electrons, so the atom gains a positive charge. 3. Compare the Mendeleev’s and the current arrangement of the periodic table. Dmitri Mendeleev was a Russian chemist who arranged the elements in the increasing atomic mass. Some elements that had similar properties were also arranged in periods. Then, there was a problem, some elements didn’t fit in this arrangement, so Henry Moseley re-arranged this organisation with the atomic number, so all the elements could fit in Mendeleev’s pattern. A TOMIC NUMBER GIVES THE IDENTITY OF THE ELEMENT, AND PROPERTIES CHANGE ACROSS THE PERIODIC TABLE. 4. Explain what data of elements can be found in the periodic table: Periodic Table: A table in which elements are arranged taking into account different properties. The mass number is not shown because of isotopes. 28 Ni Nickel 58.71 Atomic Number Chemical Symbol Name of the Element Atomic Mass 5. Determine # of: Protons, electrons and neutrons. Mass # In neutral atoms: Atomic number = Number of Protons 12 6𝐶 Number of Protons = Number of electrons Number of Neutrons= Mass number - Atomic number. Atomic # Ions Atomic number= Number of Protons Number of Neutrons = Mass number - Atomic number. Number of Electrons = Atomic Number (plus or minus) the number next to the chemical symbol. If the symbol following the element is a - , add the number next to it. (Anion) It the symbol following the element is a +, subtract the number next to it. (Cation) Examples: Cl- x the “–“represents a negative charge, so it gained 1 electron so, Atomic number plus x. Cl+ x the “+” represents a positive charge, so the atom lost an electron so, Atomic number minus x. 6. Determine atomic masses of isotopes To determine the atomic mass of an isotope, multiply the isotope and the abundance and divide it into 100. If there is more than one isotope, do the same but add them all at the end. Example: Calculate the atomic mass of Rubidium-85, which occurs at 72% and Rubidium-87 which occurs at a 28%. 85 X 72 / 100 = 61.2 87 X 28 / 100= 24.36 61.2 + 24.36 = 85.56 a.m.u 7. Identify the location and names of the groups of metals. 1. Alkali Metals 2. Alkaline Earth Metals 3-12. Transition Metals 13. Boron Group 14. Oxygen Group 14. Carbon Group 15.Halogens 15. Nitrogen Group 16.Noble Gases 8. Explain the development of the atomic theory Democritus Atom (Aristotle said we couldn’t reach the atom) Dalton All substances are made of atoms, which can´t be neither created nor destroyed. Atoms of the same element are the same Thomson Discovered electrons (Cathode-Ray Tube) Rutherford Bhor Discovered the nucleus, P+ and n. Discovered energy levels Schrodinger (Modern Theory) Electron Clouds 9. Explain the three types of radioactive decay. The nucleus of all atoms (with the exception of hydrogen) contains one or more protons and one or more neutrons. The nucleus of most carbon atoms, for instance, contains six protons and six neutrons. In most cases, the nuclei of atoms are stable; that is, they do not undergo changes on their own. A carbon nucleus will look exactly the same a hundred years from now as it does today. But some nuclei are unstable. An unstable nucleus is one that undergoes some internal change spontaneously. In this change, the nucleus gives off a subatomic particle, or a burst of energy, or both. As an example, an isotope of carbon, carbon-14, has a nucleus consisting of six protons and eight (rather than six) neutrons. A nucleus that gives off a particle or energy is said to undergo radioactive decay, or just decay. Elements with a grater atomic number of 82 (Above Lead) are radioactive. Radioactive elements emit three types of radioactive decay: A) Alpha Particles: The combination of 2 P+ and 2 N (nucleus of Helium) are ejected from the nucleus. Alpha decay usually occurs in heavy nuclei such as uranium or plutonium, and therefore is a major part of the radioactive fallout from a nuclear explosion. These are very large. Alpha particles are easy to stop; they can be stopped by a sheet of paper. Double positive charge B) Beta Particles: Beta Particles are ejected when there is beta decay. This process occurs when a neutron in the nucleus turns into an electron. It is hard to stop; it carries a negative charge and is very harmful for living organisms. C) Gamma Rays: Are high frequency electromagnetic radiation, emitted from radioactive elements. These beams are pure energy. No mass or electric charge. Penetrate through almost all materials. 10.Mention uses of isotopes: a. Carbon dating: Used to determine the age of organisms that contain Carbon. b. In surface and ground water: To determine where water existed. To explain the water cycle. c. In Nutrition: Used as tracker to mark the absorption of nutrients in the body. d. In medical uses: Used in nuclear treatment, like cancer treatment. e. Geology and Climatology: To determine the ages of rocks and tracker for the environmental processes. f. Smoke detectors: Detect the presence of smoke and heat. g. Labelling Chemical Reactions: Study of chemical changes and its process. h. Pest Control: Regulation of species defined as pest. i. Nuclear Weapons: Nuclear bombs j. Agriculture: To improve crops in many ways. k. Biological Tracing: To trace elements in humans or animals. 11.Nuclear Fusion and Fission, and Einstein’s Theory. Nuclear Fission (Division): • Uranium has not enough nuclear forces • Stretches into an elongated shape • Electric forces push it into an even more elongated shape • Electric forces > strong nuclear forces • The nucleus splits • U-235 released energy (kinetic ENERGY, ejects a neutron and gamma radiation) • Creates a chain reaction within each nucleus separating. • Nuclear energy is an important source, this works by nuclear fission. • They use Uranium as fuel. • Example: Atomic Bomb Nuclear Fusion: • Is the opposite to nuclear fission, it is a combination of nuclei • Energy is released as smaller nuclei fuse. Less mass is obtained • For a fusion reaction to occur, the nuclei must collide at a very high speed in order to overcome the mutual electric repulsion • Examples: Sun and other stars and the hydrogen bomb Einstein’s Formula: E= mc2 E= Potential Energy M= mass C= speed of light C2= constant of energy and mass This formula is very important to understand how and why energy is released in nuclear reactions. If you increase the energy, you increase the mass. When you have a bigger atom, there is enough energy. 13. What is the half-life of an element? The half life of an element is the rate of decay for a radioactive isotope; half the time is needed to an element to decay. The shorter the half life is, the faster it disintegrates. 12. Differentiate between natural and artificial transmutation. Give examples. THESE ARE EXAMPLES, BUT WHAT IS IMPORTANT IS TO UNDERSTAND THE PROCESS Transmutation is the process into which a radioactive nucleus emits an alpha or beta particle. There is a change in the atomic number, so the element changes. Natural Transmutation Artificial Transmutation. Rutherford was the first in succeeding Happens in Uranium-238 Alpha particle is ejected Uranium-238 turns into Thorium- He bombarded Nitrogen with alpha particles. 234 The Nitrogen turned into Oxygen Kinetic Energy is released The mass of the atom is affected. When a beta particle is ejected, the These experiments are made to create some synthetic elements. number changing is the atomic number 13.Explain the relation between the repulsive charges and the strong nuclear force. The strong nuclear force: Is the force that holds together the nucleus. This force acts only in short distances. When there are two much protons, the protons want to escape the nucleus. The neutrons hold together the protons, but in nucleus with more of 82 protons, the neutrons can no longer retain the protons, so radiation is emitted. 14.Benefits/Disadvantages of nuclear power. Benefits Disadvantages A source of electricity, instead of fossil Radioactive wastes that pollute rivers fuels. and others. Science progress Mutation causes by the radioactivity, for example one extra finger, or a missing finger