1. CHEMISTRY REGENTS REVIEW

2. Regents Chemistry Review Main points for each unit 1)Atomic structure: Positive nucleus surrounded by 1 or more negative electrons. Orbitals are areas of probable locations of electrons. Protons and neutrons same size (1unit), electrons very small. Lower level (closest to the nucleus) electrons are lowest energy. As you move further from the nucleus the electron shells have more energy. The # of protons identifies the element.

3. Electrons emit light when they move from the excited state back to ground state. Atomic # is the # of protons in the nucleus. Can never change if you are the same type of element. Atomic mass is the # of protons plus the # of neutrons in the nucleus. Isotopes are atoms of the same element with the same # of protons but different # of neutrons. The # of electrons equals the # of protons in an atom since all atoms are neutral.

4. Average atomic mass is….. The mass on the periodic is an average of all the naturally occurring isotopes of that element and their abundances. Multiply the mass of each isotope by its % abundance as a decimal. Move the decimal 2 places to the left. (divide by 100)

5. 1) What is the approximate mass of a proton? (1)1 u (2) 1 g (3) 0.0005 u (4) 0.0005 g 2) An electron in a sodium atom gains enough energy to move from the second shell to the third shell. The sodium atom becomes (1) a positive ion (2) a negative ion (3) an atom in an excited state (4) an atom in the ground state

6. 3) Which particle has no charge? (1)electron (2) positron (3) neutron (4) proton 4) Which quantity represents the number of protons in an atom? (1) atomic number (2) oxidation number (3) number of neutrons (4) number of valence electrons

7. 5) According to the wave-mechanical model of the atom, an orbital is a region of the most probable location of (1)an alpha particle (2) an electron (3) a gamma ray (4) a proton 6) Which particles have approximately the same mass? (1) an electron and an alpha particle (2) an electron and a proton (3) a neutron and an alpha particle (4) a neutron and a proton

8. 7) During a flame test, a lithium salt produces a characteristic red flame. This red color is produced when electrons in excited lithium atoms (1) are lost by the atoms (2) are gained by the atoms (3) return to lower energy states within the atoms (4) move to higher energy states within the atoms 8) Compared to the energy and charge of the electrons in the first shell of a Be atom, the electrons in the second shell of this atom have (1) less energy and the same charge (2) less energy and a different charge (3) more energy and the same charge (4) more energy and a different charge

9. 9) In the ground state, which noble gas has atoms with the same electron configuration as a magnesium ion? Metal atoms become ions with the noble gas configuration of the noble gas in the period above them. Non-metal atoms become ions with the noble gas configuration of the noble gas at the end of their period. Look at the periodic table for Mg. 2-8-2 Take off it’s valence shell, this is the ion electron configuration. 2-8 That is the electron configuration of Ne.

10. 11) The valence electron of which atom in the ground state has the greatest amount of energy? (1) cesium (3) rubidium (2) lithium (4) sodium 12) Explain, in terms of protons and neutrons, why I-127 and I-131 are different isotopes of iodine.

11. 13) What is average atomic mass of Lithium if 7.42% exists as 6 Li (6.015 g/mol) and 92.58% exists as 7 Li (7.016 g/mol)? (.0742) (6.015) + (.9258) (7.016) = 14) Without doing any math, are there more Bromine-79 atoms or more Bromine-80 atoms on earth? (Hint: look at the periodic table.)

12. Periodic table

13. 2) Periodic Table: Arranged by increasing atomic #. Metals are to the left of the steps (most elements are metals) good conductors, malleable. Non-metals are to the right of the steps. Poor conductors, brittle. Metalloids are on the steps and the 2 below in the center. (Ge and Sb) Properties of both metals and non-metals. Electronegativity is an atoms attraction for another atoms electrons.

14. Ionization energy is how tightly an atom holds onto it’s own electrons. Both of these go up or down together. Top right (F) has the highest electronegativity and IE values. Bottom left (Fr) has the lowest electronegativity and IE values. Periods go across (rows, horizontal) and represent the # of occupied electron shells an element has.

15. Groups or families are columns and represent the # of valence electrons an element has. Valence electrons are the shell farthest from the nucleus. Valence electrons are the ones which are involved in bonding. Lewis dot diagrams are the atomic symbol surrounded by dots. There is 1 dot for each valence electron, no more than 2 per side, no more than 8 total. Elements in the same group behave the same way (react) because they have the same # of valence electrons.

16. Atomic radius increases as you move down a group because you are adding electron shells. Atomic radius decreases as you go across a period because there are more protons in the nucleus pulling on the same # of electron shells so the atomic radius is smaller. BrINClHOF always exist as diatomic molecules at STP. Br and Hg are the only 2 liquids Start at 7. Make a 7. 17, He and H are gases at STP.

17. Use Table S to find trends in electronegativity, ionization energy and atomic radius. Also use table S for density, BP, MP

18. Periodic table questions

19. 1) At STP, which element is a good conductor of electricity? (1)chlorine (2) silver (3) iodine (4) sulfur 2) Which elements have the most similar chemical properties? (1) boron and carbon (2) oxygen and sulfur (3) aluminum and bromine (4) argon and silicon

20. 3) Which general trends in first ionization energy and electronegativity values are demonstrated by Group 15 elements as they are considered in order from top to bottom? (1) The first ionization energy decreases and the electronegativity decreases. (2) The first ionization energy increases and the electronegativity increases. (3) The first ionization energy decreases and the electronegativity increases. (4) The first ionization energy increases and the electronegativity decreases.

21. 4) There are six elements in Group 14 on the Periodic Table. One of these elements has the symbol Uuq, which is a temporary, systematic symbol. This element is now known as flerovium. Identify an element in Group 14 that is classified as a metalloid. Explain, in terms of electron shells, why each successive element in Group 14 has a larger atomic radius, as the elements are considered in order of increasing atomic number. State the expected number of valence electrons in an atom of the element flerovium in the ground state.

22. 5) In a bond between an atom of carbon and an atom of fluorine, the fluorine atom has a (1) weaker attraction for electrons (2) stronger attraction for electrons (3) smaller number of first-shell electrons (4) larger number of first-shell electron Use Table S for electronegativity, which is higher.

23. 6) As the elements in Period 3 are considered in order of increasing atomic number, there is a general decrease in (1) atomic mass (2) atomic radius (3) electronegativity (4) first ionization energy 7) Which electron configuration represents the electrons of a sulfur atom in an excited state? (1) 2-6-6 (2) 2-8-4 (3) 2-7-7 (4) 2-8-6

24. 8) What is formed when two atoms of bromine bond together? (1) a monatomic molecule (2) a diatomic molecule (3) a heterogeneous mixture (4) a homogeneous mixture 9) Which term represents the attraction one atom has for the electrons in a bond with another atom? (1) electronegativity (2) electrical conductivity (3) first ionization energy (4) mechanical energy

25. 3) ions: An ion is an atom which has an imbalance between protons and electrons. Positive ions are called cations and have more protons than electrons. Positive ions have lost electrons. You can not change the # of protons an atom has. Losing electrons is called oxidation. Positive ions are smaller than their associated atom because they have lost electrons. Metals tend to form positive ions.

26. Negative ions are called anions and have more electrons than protons. Negative ions have gained electrons. Gaining electrons is called reduction, your ionic charge is reduced. Negative ions are larger than their associated atom because they have gained electrons. Non-metals tend to form negative ions.

27. All atoms want to have 8 valence electrons. 8 valence electrons is the most stable electron configuration. Noble gases (group 18) have 8 valence electrons The charge of the ion tells you how many electrons were gained or lost.

28. 1) Which ion has the smallest radius? (1)O 2– (2) Se 2– (3) S 2– (4) Te 2– 2) What is the overall charge of an ion that has 12 protons, 10 electrons, and 14 neutrons? (1)2 (2) 4 (3) 2 (4) 4 3) What is the number of electrons in an Al 3+ ion? (1) 10 (2) 3 (3) 13 (4) 16

29. Chemistry is the study of Matter Matter is anything that has mass and takes up space (volume) All matter is made of atoms. #allatomsmatter.

30. 4 ) Matter: Matter is either an element, a compound or a mixture. Elements are the simplest form of matter. Elements can not be broken down by a chemical change (reaction). Compounds are 2 or more atoms chemically bonded to each other. Compounds can be broken down by a chemical reaction (change) The proportion of elements in a compound is fixed, always the same. A substance is either a compound or an element.

31. A mixture is 2 or more elements or compounds or 1 of each mixed together in the same container but NOT chemically bonded. The proportion of substances in a mixture varies from sample to sample. 2 types of mixtures: Homogeneous (homo = same)mixtures are also called solutions. Homogeneous mixtures look the same throughout, uniform, you can’t see the different substances in it. Heterogeneous mixtures (hetero = different) do NOT look the same throughout, you can see the different substances in it.

32. Mixtures can be separated by their physical properties. Distillation separates mixtures based on BP. Filtration separates mixtures based on particle size. Evaporation separated based on solubility. Chromatography separates based on polarity.

33. 1) Which two gases can not be broken down by chemical means? (1)CO and He (2) Xe and He (3) CO and NH3 (4) Xe and NH3 2) Two substances in a mixture differ in density and particle size. These properties can be used to (1) separate the substances (2) chemically combine the substances (3) determine the freezing point of the mixture (4) predict the electrical conductivity of the mixture

34. 3) Salt water is classified as a (1) compound because the proportion of its atoms is fixed (2) compound because the proportion of its atoms can vary (3) mixture because the proportion of its components is fixed (4) mixture because the proportion of its components can vary

35. 4) Powdered iron is magnetic, but powdered sulfur is not. What occurs when they form a mixture in a beaker at room temperature? (1) The iron retains its magnetic properties. (2) The iron loses its metallic properties. (3) The sulfur gains magnetic properties. (4) The sulfur gains metallic properties.

36. 5) A sample of CO2(s) and a sample of CO2(g) differ in their (1) chemical compositions (2) empirical formulas (3) molecular structures (4) physical properties 6) Two grams of potassium chloride are completely dissolved in a sample of water in a beaker. This solution is classified as (1) an element (2) a compound (3) a homogeneous mixture (4) a heterogeneous mixture

38. 5) Bonding: All bonds are the result of the attraction of an atoms nucleus (protons) for another atom’s electrons. Energy is absorbed when breaking a bond, therefore breaking bonds is an endothermic reaction. Energy is released when bonds are formed, therefore forming bonds is an exothermic reaction. Atoms form bonds to achieve a stable octet. (8 valence electrons.) 1 covalent bond is 2 electrons (1 pair)

39. Metallic bonds are formed between 2 atoms of the same metal element. Electrons flow among the nuclei of the metal atoms. Metallic bonds are a “sea of mobile electrons.” This flow allows metals to be malleable.

40. Ionic bonds are the transfer of valence electrons from a metal atom to a non-metal atom. Compounds with a polyatomic ion have both ionic and covalent bonds but form ionic compounds. The difference in electronegativity values between the 2 atoms involved in the bond is greatest in ionic bonding. (1.7 or greater) Ionically bonded substances are called salts. Salts are hard and have high MP. Salts do not conduct electricity as solids but do in liquid or aq states.

41. Covalent bonds are formed when 2 atoms share their valence electrons. Co = together, valent = referring to the valence shell. Occurs between 2 non-metal atoms. difference in electronegativity values between the 2 atoms involved in the bond is less than 1.7

42. 2 types of covalent bonds: Polar bonds are an unequal sharing of electrons. The atom with the higher electronegativity value gets a slight negative charge and the 1 with the lower electronegativity value gets a slight positive charge. 2 different non-metal atoms. Non-polar bonds are an equal sharing of electrons. Non-polar bonds are between 2 atoms of the same nonmetal element.

43. Polar vs nonpolar molecules: S ymmetrical N onpolar A symmetrical P olar Nonpolar molecules can have polar bonds! Nonpolar molecules formulas end in an even # polar molecules formulas end in an odd #

44. 1) Which formulas represent one ionic compound and one molecular compound? (1) N 2 and SO 2 (2) BaCl 2 and N 2 O 4 (3) Cl 2 and H 2 S (4) NaOH and BaSO 4 2) Given the balanced equation representing a reaction: N 2 energy → N + N Which statement describes this reaction? (1) Bonds are broken, and the reaction is endothermic. (2) Bonds are broken, and the reaction is exothermic. (3) Bonds are formed, and the reaction is endothermic. (4) Bonds are formed, and the reaction is exothermic.

45. 3) Which statement describes a multiple covalent bond? (1) Two electrons are shared. (2) Four electrons are shared. (3) Two electrons are transferred. (4) Four electrons are transferred. 4) The electronegativity difference between the atoms in a molecule of HCl can be used to determine (1) the entropy of the atoms (2) the atomic number of the atoms (3) the first ionization energy of the atoms (4) the polarity of the bond between the two atoms

46. Rubbing alcohol is a product available at most pharmacies and supermarkets. One rubbing alcohol solution contains 2-propanol and water. The boiling point of 2-propanol is 82.3°C at standard pressure. Explain, in terms of electronegativity differences, why a C O bond is more polar than a C H bond. Identify a strong intermolecular force of attraction between an alcohol molecule and a water molecule in the solution. Explain, in terms of charge distribution, why a molecule of the 2-propanol is a polar molecule.

47. Which statement explains why a CO2 molecule is nonpolar? (1) Carbon and oxygen are both nonmetals. (2) Carbon and oxygen have different electronegativities. (3) The molecule has a symmetrical distribution of charge. (4) The molecule has an asymmetrical distribution of charge.

48. Phases of matter: Solids have crystal structure and the lowest entropy because they are the most organized. Liquids have more entropy than solids Gases have the most entropy.

49. Systems in nature tend to undergo changes toward (1) lower energy and higher entropy (2) lower energy and lower entropy (3) higher energy and higher entropy (4) higher energy and lower entropy

50. When does a substance boil? When the vapor pressure = atmospheric pressure The weaker the forces of attraction = higher vapor pressure = lower BP. See table H

51. Using table H, which substance has the: Lowest boiling point ____________________ Strongest forces of attraction ______________________ Greatest polarity ________________________ Lowest vapor pressure ______________________ So the substance that boils at the ___________________ temperature will have the ________________________ intermolecular forces.

52. Avogadro’s hypothesis Which containers have the same number of molecules? The ones that have the SAME VOLUME. 5 LITERS 6 LITERS 5 LITERS 30 0 60 0 20 0

53. When does PE change? When does KE change? Where is the section for heat of fusion? Where is the section for heat of vaporization? Where is the section for change in temp? If this is water what is the temp at D and C? Calculate the heat for each section? 50 g water

54. Ideal Gases: No forces of attraction between molecules Molecules have no volume Colliding results in a transfer of energy with no loss of energy. Best conditions (when gases act most like an ideal gas) high temp and low pressure. Move in rapid, random, straight line motion. H and He are the most like ideal gases.

55. What is this picture showing?

56. 2.00 L of a gas is collected at 25.0 °C and 99.3 kPa. What is the volume at STP? P1 = V1= T1= P2= V2= T2= Don’t Forget to change T to K!!!

57. Cylinder A has a movable piston and contains hydrogen gas. An identical cylinder, B, contains methane gas. The diagram below represents these cylinders and the conditions of pressure, volume, and temperature of the gas in each cylinder. Compare the total number of gas molecules in cylinder A to the total number of gas molecules in cylinder B. State a change in temperature and a change in pressure that will cause the gas in cylinder A to behave more like an ideal gas. In the space in your answer booklet, show a numerical setup for calculating the volume of the gas in cylinder B at STP.

58. Heat always moves from the hotter substance to the colder substance.

59. A student made a copper bracelet by hammering a small copper bar into the desired shape. The bracelet has a mass of 30.1 grams and was at a temperature of 21°C in the classroom. After the student wore the bracelet, the bracelet reached a temperature of 33°C. Later, the student removed the bracelet and placed it on a desk at home, where it cooled from 33°C to 19°C. The specific heat capacity of copper is 0.385 J/gK. Explain, in terms of heat flow, the change in the temperature of the bracelet when the student wore the bracelet. 1. Determine the number of moles of copper in the bracelet. 2. Show a numerical setup for calculating the amount of heat released by the bracelet as it cooled on the desk. 3. Explain, in terms of chemical activity, why copper is a better choice than iron to make the bracelet. What table do you use here????

61. Gram formula mass = the mass of one mole of a substance Use the periodic table and add up the masses Use the formula from table T to calculate the number of moles of a substance when given the mass.

62. Which quantity is equal to one mole of Au? (1) the atomic mass in grams (2) the atomic number in grams (3) the mass of neutrons in grams (4) the number of neutrons in grams

63. Given the balanced equation representing the reaction between methane and oxygen: CH 4 + 2O 2 → CO 2 2H 2 O According to this equation, what is the mole ratio of oxygen to methane?

64. The balanced equation below represents the reaction of glucose, C 6 H 12 O 6, with oxygen at 298 K and 101.3 kPa. C 6 H 12 O 6 (s) 6O 2 (g) → 6CO 2 (g) 6H 2 O(ℓ) Determine the mass of CO 2 produced when 9.0 grams of glucose completely reacts with 9.6 grams of oxygen to produce 5.4 grams of water. Compare the entropy of the reactants to the entropy of the products. Write the empirical formula for glucose.

65. Use this formula when you are asked for molarity and no acid or base is mentioned and NO TITRATION OR NEUTRALIZATION IS MENTIONED. They just want the concentration of a solution.

66. Use Table F when you are finding out if a substance is soluble in water or not. And to determine which substance dissolves the most to give the greatest concentration of dissolved substances.

67. Use Table G when you need to know how much solute dissolves in 100 grams of water at a certain temperature. Which ones are the gases???

68. Are the following solutions saturated, unsaturated or supersaturated? (Plot the point and see where it falls in relation to the substance curve) 60 g KCl at 70 degrees. 90 g KNO 3 at 60 degrees. 110 g NaNO 3 at 45 degrees. 10 g KClO 3 at 10 degrees. 60 g NH 4 Cl at 70 degrees.

69. How many grams must be added to make a saturated solution? (draw a line up the temp till you hit the curve for that substance and read the grams) NaNO 3 at 30 degrees. KClO 3 at 70 degrees. KNO 3 at 45 degrees. KCl at 40 degrees. NaCl at 90 degrees.

70. Be careful of the amount of water stated in the question: What is the maximum # of grams of KNO 3 That will dissolve in 200 cc water at 20 degrees? Figure it for 100 cc and then double the amount. For 50cc ½ the amount.

71. 1.When do molecules make Effective collisions? a. They collide with the correct angle or orientation b. they collide with sufficient energy ( due to the high temperature or lowering the activation energy) Then the activated complex is produced which turns into product. 2. How does a catalyst speed up the rate of reaction??? LOWERS THE ACTIVATION ENERGY A catalyst affects both the forward and reverse reaction so no change in equilibrium/ 3.What is the formula for the heat of reaction??? H= Hp-Hr 4.See Table I for all heats of reaction -H= exothermic +H = endothermic

72. Use Table J to see which metals are more reactive than others (Top more reactive than bottom.) Higher up ones give electrons to lower down ones. That’s oxidation. Metals listed above H will react with acid to form hydrogen gas. (Good acid test)

73. Arrhenius Acids: Lose H+ See table K They start with H The H bonds to water to form H 3 O + aka hydronium The amount of hydronium decides the pH The more hydronium H 3 O + the more acidic A pH of 2 is ___________________x ____________acidic than a pH of 4.because it has _____ hydronium.

74. Bronsted Lowry Acid proton donor Bronsted Lowry Base proton acceptor Pick out the two acids and the two bases

75. Use titration formula when an acid is mixing and neutralizing a base. Bases are on table L. How do you recognize a base????? How do you tell the difference btwn base and alcohol???

77. What kind of cell is this? Voltaic cell: The voltmeter measures current. Is it spontaneous? Yes What is the purpose of the salt bridge? Migration of ions? What is happening? Electrons are transferred. What is losing electrons and what is that half cell called? The zinc metal is the ANODE What process is taking place? Oxidation What is happening in the other half cell? Reduction at the CATHODE: GAINING ELECTRONS What happens to the masses of the electrodes? The anode decreases and the cathode increases Summary: A CHEMICAL REACTION CREATES AN ELECTRIC CURRENT.

78. What happens to the masses of the electrodes? THE ANODE DECREASES IN MASS AS THE ZINC IONS GO INTO SOLUTION. THIS WILL INCREASE THE CONCENTRATION OF THAT SOLUTION. THE CATHODE INCREASES IN MASS AS THE COPPER IONS COME OUT OF SOLUTION AND PLATE ONTO THE CATHODE. THIS WILL DECREASE THE CONCENTRATION OF THAT SOLUTION. SUMMARY: A CHEMICAL REACTION CREATES AN ELECTRIC CURRENT.

79. Zn --------------------------------  Zn +2 + 2e- Cu +2 + 2e- -------------------  Cu The number of e- lost has to equal the number of e- gained (conservation of charge)

80. In this setup a battery is provided. Why is this necessary? To provide a source of electrons. This is a non spontaneous reaction. Which reaction requires the electrons? The reduction of sodium(Na) What is the chloride ion doing? Losing electrons and being oxidized. This shows how pure alkali metals can be obtained. Remember that group one and group two metals are never found alone in nature as free elements. This is called the electrolysis of a fused (melted) salt. Where are the anode and the cathode? What happens there?? Oxidation at the anode and reduction at the cathode

81. The cathode is always attached to the negative terminal of the battery!!!!!!! Is this balanced? How can we balance it? Put a 2 in front of everything in the sodium reduction half reaction

82. SUMMARY: IN ELECTROLYSIS A BATTERY IS NEEDED TO PROVIDE ELECTRONS. THIS IS A NON SPONTANEOUS REACTION THE CATHODE IS NEGATIVE AN ELECTRIC CURRENT CREATES A CHEMICAL REACTION

83. Nuclear Chemistry: Table O tells you the mass and charge of the nuclear particles Radioactivity means that one element changes into another element by giving off pieces from the nucleus of the atoms. It is called a TRANSMUTATION. NATURAL TRANSMUTATION: ARTIFICIAL TRANSMUTATION:

84. Nuclear chemistry Types of radiation, half-life, decay modes, nuclear reactions and uses of nuclear radiation.

85. TimeOriginal MassFraction remaining 0 At the beginning100g1/1 First half life100/2=50g1/2 Second half life50/2=25g1/4 Third half life25/2=12.5g1/8 Fourth half life 12.5/2= 6.25g 1/16 Fifth half life 6.25/2=3.125g 1/32 Sixth half life 3.125/2= 1.56g 1/64 Use a Chart like this to do half- life. Get the half- life from table N.

86. HALF LIFE QUESTIONS 1. If 1/8 of an original sample of krypton-74 remains unchanged after 34.5 minutes, what is the half-life of krypton-74? 2. What is the half-life of sodium-25 if 1.00 gram of a 16.00gram sample of sodium-25 remains unchanged after 237 seconds? 3. After 32 days, 5 milligrams of an 80-milligram sample of a radioactive isotope remains unchanged. What is the half-life of this element? 4. What fraction of a radioactive 90 Sr sample would remain unchanged after 56.2 years? 5. What fraction of a sample of gold-198 remains radioactive after 2.69 days? 6. Which radioactive isotope will retain only one-eighth its original radioactive atoms after approximately 43 days? 1. Au-198 2. I-131 3. P-32 4. Ra-222 7. What fraction of an original Co-60 sample remains after 21 years?

87. 8.How many days are required for 200 grams of radon-222 to decay to 50 grams? 9.What is the number of hours required for potassium-42 to undergo 3 half-life periods? 10.What was the original mass of a radioactive sample that decayed to 25 grams in four half-life periods? 11. The graph represents the decay curve of a radioactive isotope. How do you use this graph to find the half life of the isotope?

88. ANSWERS TO HALF LIFE QUESTIONS 1.1/8 means 3 half lives have passed. The time it took was 34.5 minutes. 34.5/3=11.5 minutes 2. 16g/2 = 8g(1 st half life) 8/2=4g(2 nd half life) 4/2=2g(3 rd half life) 2/2=1g(4 th half life) So 4 half lives took place in 237 seconds. 237/4= 59.3 seconds 3. 80/2= 40 40/2=20 20/2=10 10/2=5 milligrams So 4 half lives took place in 32 days. 32/4= 8 days is the half life of the isotope. 4. Total time divided by half life tells you the number of half lives. 56.2/29.1(Table N)= approx. 2 half lives. After two half lives we know that ¼ of the original remains. 5. 2.69 days/2.69 days = 1 half remains = ½ 6. One eighth means three half lives would have to take 43 days. 1. Au-198 2. I-131 3. P-32 4. Ra-222

89. 7. Co-60 has a half life of 5.271 years. The total time was 21 years. 21/5.271= 4 half lives = 1/16 of original 8. 200/2=100 100/2=50 That is 2 half lives. Ra-222 has a half life of 3.823days so 2 half lives would be 3.82x 2 = 7.64 days 9. The half life of K-42 is 12.36 hours. 12.36 x 3 = 37 hours.

90. 10.Instead of dividing by 2 each time, we will multiply by 2 each time since we have to end up with more for the answer. 25 x 2= 50 grams (1) 50 x 2 =100 grams(2) 100 x 2 = 200 (3) 200 x 2 = 400 grams. So if you end up with 25 grams after 4 half lives, then you started out with 400 grams. 11.Find a number on the y-axis. Cut it in half. Find that # on the y- axis. Use the curve to see how much time it took using the X-axis. The answer for this graph is 3 seconds. and 48 days for the other graph.

91. Types of Nuclear Reactions Fission Large atoms split into smaller atoms Usually starts with uranium being bombarded with neutrons. Happens in a nuclear reactor at a nuclear power plant. Releases tremendous amounts of energy. Much more than any other reaction on earth. Some mass is converted to energy. It is called a MASS DEFICIT Fusion Small atoms come together to make a larger atom. Hydrogen with hydrogen make helium Happens on the Sun Has not been reproduced on earth. Releases tremendous amounts of energy. Much more than any other reaction on earth. Some mass is converted to energy. It is called a MASS DEFICIT

93. What are the reactants in this picture??? What reaction is this and how do you know?

94. Uses of Radioisotopes How radiation is used to help builders, doctors, medical patients and homeowners

95. Smoke Alarms Agricultural applications Food Irridation Detect cancer and treat cancer

96. Ages of rock layers Ages of fossils Detect thyroid problems

97. 10) A breeder reactor is one type of nuclear reactor. In a breeder reactor, uranium-238 is transformed in a series of nuclear reactions into plutonium-239. The plutonium-239 can undergo fission as shown in the equation below. The X represents a missing product in the equation. Determine the number of neutrons in an atom of the uranium isotope used in the breeder reactor. U-238 U always has 92 protons, so 238 – 92 = 146