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Arnoldi Honors Chemistry Atomic Theory One Review Key 1. Definitions a. Atoms the smallest piece of an element that still retains the properties of that element b. Atomic Number # of protons in the nucleus c. Mass Number the sum of the protons and neutrons in the nucleus this is for one particular isotope d. Nucleons particles that make up the nucleus (neutron and proton) e. anion negatively charged particle f. cation positively charged particle g. ion any charged particle h. isotopes atoms of the same element with different masses i. Quantum an exact amount of energy j. Quanta plural of quantum k. Photon light energy l. Radioactivity Spontaneous disintegration in which small particles of matter (alpha or beta particles) and /or electromagnetic radiation (gamma rays) are emitted by unstable atomic nuclei m. Electromagnetic Radiation n. Half-Life a form of energy that exhibits wavelike behavior as it travels through space the time it takes for a sample of radioactive matter to decay to half its original size 2. How do we see individual atoms? use a scanning tunneling microscope 3. Which of the following appear on the periodic table? Atomic Number Atomic Mass 4. What controls the identity of the atom? Mass Number atomic number (number of protons) 5. Subatomic Particles: Particle Charge Location in Atom In Nucleus + Mass (Two Ways) 1 amu 1.67 X 10-24 grams Proton Electron - Negligible (so small as to be insignificant) In Orbitals (outside of nucleus) Neutron neutral 1 amu (atomic mass unit) In Nucleus 6. What controls the charge of the particle? Electrons 7. How do we form cations? Lose electrons 8. How do we form anions? Gain electrons 9. Describe Quarks Quarks make up protons and neutrons. There are six types of quarks, (up, down, beauty, truth, charmed, strangeness) 10. Why do isotopes have different masses? They have different numbers of neutrons. 11. What are the three isotopes of hydrogen? Protium, deuterium, tritium 12. Fill in the following table: Isotope 41 Ca+2 4 He 16 O-2 235 U P-3 Protons Electrons Neutrons 20 18 21 2 2 2 8 10 8 92 92 143 15 18 16 13. Compare Continuous and Discontinuous matter theories. Matter is one continuous piece, or matter can be broken down into smaller pieces. (You can only buy a whole sub, or you can buy a slice of pie). 14. Fill in the Blanks Democritus was a Greek philosopher who first used the term “atom”, which means indivisible. He thought atoms were tiny and indestructible. He created the Discontinous theory of matter, which stated that matter is not one continuous piece. 15. Fill in the Blanks In the 18th century, we had the first experimental evidence that could support the idea of an atom. Antoine Lavoisier discussed the Law of Conservation of Mass, and Joseph Proust discussed the Law of Definite Proportions, which states that a chemical compound contains the elements in exactly the same proportions by mass, regardless of the size of the sample or source of the compound. 16. Fill in the Blanks John Dalton discussed the Law of Multiple Proportions which stated that if two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element, combined with a certain mass of the first element, is always a ratio of small whole numbers. Dalton stated four thoughts about atomic theory: (1) All matter is made up of atoms which are indivisible and indestructible, (2) Atoms of the same element are identical – in particular their masses are the same, (3) Atoms of different elements are completely different, in particular their masses are different, and (4) compounds. Atoms combine in simple whole number ratios to form (They due this via chemical reactions which are the result of the separating or combining of atoms. Dalton’s atomic model was a Billiard Ball. 17. Fill in the Blanks Today, we agree that matter is made of atoms, atoms do combine in simple whole number ratios, and chemical reactions are the result of the separating /combining of atoms. 18. Fill in the Blanks However, we disagree with some of Dalton’s ideas, because we know that atoms are divisible into subatomic particles, and atoms are destructible via nuclear reactions (we can create atoms in nuclear reactions, also). Also, atoms of different elements can have the same mass, and atoms of the same element can have different masses because of isotopes. 19. Fill in the Blanks A guy named William Crookes had the next impact on atomic theory. Crooke’s studied the behavior of gases in vacuum tubes (aka cathode ray tubes), which were the forerunners of picture tubes in television. Crookes theorized that some kind of radiation or particles was traveling from the cathode across the tube. He called this radiation cathode rays. Draw a cathode ray tube below. Label the + and - charges, the cathode ray, and the cathode and anode cathode ray (must start at the cathode and move toward the anode) 20. Fill in the Blanks J.J. Thomson used Crookes tube to discover the electron. He determined that the electron had a negative charge by bending the ray in the Cathode Ray tube using + and – fields. The ray bent toward the positive field. The ray bent away from the negative field. From this data, and knowing that likes repel and opposites attract, Thomson decided that since the ray is attracted to the positive field, and repelled by the negative field, it must be negative. Thus, he determined that the cathode ray is a stream of negatively charged which he called electrons. His atomic model was called the Plum Pudding model. 21. Fill in the Blanks Thomson and Milliken worked together on the Oil Drop Experiment in which they discovered the mass of the electron to be 9.11 X 10-28 grams which is nearly negligible. This can also be expressed as 1/1837 amu. (protons and neutrons have a mass of 1 amu). They also determined that the charge is 1.602X10-19 coulomb which this is the smallest charge ever detected. 22. Fill in the Blanks The next major contributor to Atomic Theory was Eugene Goldstein who in 1886 found evidence for the proton. 23. Fill in the Blanks Rutherford used the Gold Foil Experiment to discover the atom’s nucleus. Give a basic rendering of this experiment below. Rutherford bombarded gold foil with alpha particles which are positively charged Helium atoms. He saw that most of the particles went through, but a few were deflected. Since alpha particles are positive, they must have hit something positive inside of the atom (likes repel). From these results, Rutherford concluded that there is a small, dense, positively charged center in the atom, which he called the nucleus. He also concluded that the atom is mostly empty space, and that the bulk of the mass of the atom is in the center. Rutherford knew that the electrons where outside the nucleus, occupying most of the volume of the atom. However, he couldn’t explain why, if electrons are negative, and the center of the atom is positive, they weren’t attracted to the center of the atom. alpha particles deflection most go through 24. Fill in the Blanks James Chadwick confirmed the existence of the neutron by bombarding beryllium atoms with alpha particles via the following equation: 4 9 He + 2 12 Be 1 C 4 + n 0 6 25. Fill in the Blanks Niels Bohr said that electrons reside in energy levels, aka energy shells. The energy of the level increases as the distance from the nucleus increases, and electrons fill the energy levels from the inside out, or from low to high energy. Atoms can be found in the ground state or the excited state. A ground state atom will fill the first shell before moving to the second, the second before moving to the third, etc. The last shell (the outermost shell) may or may not be filled. This is the lowest possible energy state. An excited state atom has an inside shell that is NOT filled before moving to the next shell. It is NOT in the lowest possible energy state. Another name for the ground state is the stable state. Another name for the excited state is the unstable state. To move from one shell to another, or to move from one energy level to another, you must gain or lose the exact amount of energy between those two levels. 26. Draw a Bohr Diagram for each of the following: a. Lithium Atom 3p ) 2e- )1e- b. Phosphorus Ion 15 p )2e- )8e- )8e- c. Potassium Ion 19 p )2e- )8e- )8e- 27. What is an alpha particle? a positive helium atom Complete the following alpha particle radiation equation below: 4 He 2 + 9 Be 4 12 C 6 1 + n 0 28. What is a beta particle? an electron Complete the following beta particle radiation equation below: 234 Th 90 29. What is a Gamma Ray? 234 Pa 91 0 e -1 high energy electromagnetic radiation 30. The half-life of iodine-131 is 8 days. What mass of this isotope remains from a 4.00 g sample after 32 days? forward in time, divide by 2 Amount 4.00g 2.00g 1.00g 0.50g Time 0 days 8 days 16 days 24 days 0.25g 32 days forward in time, add half life 31. The starting mass of a radioactive isotope was 20.0g. Its half-life is two days. The mass is now 2.5g. How old is the sample? forward in time, divide by 2 Amount 20.0g 10.0g 5.0 g 2.5 g Time 0 days 2 days 4 days 6 days forward in time, add half-life 32. A sample of radioactive matter has a mass of 10.5g. It is 24 hours old, and its half-life is 6 hours. What was the original mass of the sample? back in time, multiply by 2 Amount 10.5 g 21.0g 42.0g 84.0g 168 g Time 0 hours 6 hrs ago 12 hrs ago 18 hrs ago 24 hrs ago back in time, add half-life “ago” PROBLEMS 12 1. What is the atomic mass for element B? 13 B = 82.20% B = 17.80 % (12.008 u) (82.20) + (13.092u) (17.80) = 100 12.008 amu 13.092 amu 12.201 amu 2. Find the %’s of 2 isotopes of element X given the following information: average atomic mass = 4.1989 isotope 1 = 4X isotope 2 = 5X [(4amu)(x)] + [(5amu)(100-x)] 100 4x + 500 - 5x -1x = 4.1989 amu = (4.1989) 100 = -80.11 x 100 – x = 80.11 % = 19.89% 3. Element Q consists of two naturally occurring isotopes: Isotope One’s abundance is 43.55 % and its mass is 40.009 amu. If the average atomic mass of the element is 41.956 amu, what is the percent abundance and exact mass of the other isotope? Percent Abundance 100 – 3.55 = 56.45% Mass of Second Isotope [(40.009 amu)(43.55)] + [(x amu)(56.45)] 100 1742039195 u + = 41.956 amu 56.45X = 4195.6 amu 56.45 X = 2453.20805 x = 43.458 u