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UNIT 2 ATOMS, MATTER, AND THE MOLE I. CHEMISTRY - The study of matter and the changes it undergoes. A. . Matter is categorized into two types: 1. Heterogeneous –“not the same throughout”. Each part has different physical properties. Most mixtures fall into this category. EX: milk is a heterogeneous mixture made up of water, fats (cream), protein (casein and whey) and lactose and can be separated into its components. 2. Homogeneous – “the same throughout”. Compounds and elements are pure substances and are homogeneous. Solutions are homogeneous mixtures that have a uniform, though varying, distribution of particles (solute) in a dissolving material (solvent). B. MATTER is anything that has mass and occupies space. It is further subdivided into three general classes, based on chemical or physical properties: 1. Compound – a pure substance composed of 2 or more elements which has new properties of its own unlike the properties of the original substances. EX: table salt is sodium chloride-a white crystalline substance with a high melting point. Sodium is a metallic element and chlorine is a yellowgreenish gas. 2. Element – a substance composed of only one kind of atom that can no longer be decomposed by ordinary chemical means. EX: silver, nitrogen. 3. Mixture – a material composed of 2 or more substances, each of which retains its own physical properties. Mixtures can be heterogeneous or homogeneous (also called a solution). II. THE CHANGES THAT MATTER UNDERGOES A. PHYSICAL PROPERTIES – characteristics that undergoes no change in composition. EX: mass, length, volume, density, solubility, melting and boiling point, conductivity, color, hardness. Mixtures are separated using their physical properties. B. PHYSICAL CHANGE- changes in which no new kinds or matter are formed. EX: phase changes (freezing, boiling and melting), grinding, dissolving. Mixtures can be separated by physical separation-filtration, evaporation, thawing, distillation, precipitation, boiling. C. CHEMICAL PROPERTIES- describes how a substance changes into something new. By asking questions such as does it burn or react with acids helps determine the chemical properties of a substance. D. CHEMICAL CHANGES – changes that produce new kinds of matter that show brand new properties. (ex.) Combustion (burning), composition and decomposition, color changes, energy changes, light emitted, gas given off, precipitation, pH changes. Compounds are the products of chemical changes. They cannot be broken down physically, but can be separated chemically. E. LAW OF DEFINITE COMPOSITION-states that a compound always contains elements in certain definite compositions by having the same percentage by mass of each element in the compound. 1. EX: water has the formula H2O, which means for one atom of oxygen there are two atoms of hydrogen. 2. H2O2 is not water. It is called hydrogen peroxide, has two atoms of hydrogen for every two atoms of oxygen and behaves much differently that water. This brings us to the next law. F. LAW OF MULTIPLE PROPORTIONS-states that there can exist two or more compounds with different proportions of the same elements. 1. EX: water and hydrogen peroxide both contain hydrogen and oxygen in definite composition, but in a different proportion to each other. 2. Methane (CH4) and butane (C4H10) are also good examples. 3. What are two compounds that contain carbon and oxygen? III. THE STRUCTURE OF THE ATOM – smallest unit of an element A. Consists of two main parts held together by an electro-magnetic force: 1. NUCLEUS-central (most dense) part that contains 2 types of subatomic particles. a. Protons- have a positive (+) charge. b. Neutrons-have a neutral (o) charge. c. Both particles contribute the majority of the mass to the nucleus and are held together by the strong force. 2. ELECTRON CLOUD- surrounds the nucleus. It contains one type of subatomic particle. a. Electrons have a negative () charge. b. Electrons are all identical. c. The mass of an electron is negligible compared to the rest of the atom. d. They move about the atom with different energies that are relative to their distance from the nucleus, e. If the nucleus were 1 cm. in diameter, the electrons would be found 48 m or ½ football field away. B. RULES CONCERNING CHARGES: opposite charges attract and like charges repel. 1. Particles with the same charge (+ and +) or ( and ) push each other away. 2. Particles with opposite charges (+ and ) are drawn to each other. 3. Two questions: a. What keeps the electrons from falling into the positively charged nucleus? b. What keeps the protons in the nucleus from repelling each other? IV. “ATOMIC FACTS” FROM THE PERIODIC TABLE A. TERMS YOU MUST KNOW: 1. Atomic number-number of protons in the nucleus 2. Mass number- number of protons and neutrons in the nucleus. It is always a whole number. Have you ever heard of 2/3 of a neutron? 3. Atomic mass-the mass of an atom expressed in atomic mass units (AMU’s), a very tiny weighing scale for atoms. B. DETERMINING THE ATOMIC NUMBER, MASS NUMBER AND ATOMIC MASS NUMBER FROM THE PERIODIC TABLE. 1. Atomic number- on the periodic table, it is the whole number listed. 2. Atomic mass number – on the periodic table, it is the larger number listed with a decimal because it is an average of all isotopes of that element. 3. Mass number – not directly found on the periodic table, but is may be determined by rounding the atomic mass number to the nearest whole number. C. DETERMINING THE NUMBER OF NEUTRONS: not given directly on the periodic table. 1. Subtract the atomic number from the mass number. Mass number (protons and neutrons) atomic number (protons) = [larger number] [smaller number] number of neutrons D. EXAMPLE: 1. 2. 3. 4. 5. 6. mass number neutrons electrons protons mass in AMU’s atomic number 11 6 5 5 10.81 amu 5 E. CONVENTIONAL WAY OF WRITING ELEMENT WITHOUT USE OF PERIODIC TABLE Mass number 39 K Atomic number 19 EX: the whole numbers indicate the mass numbers oxygen-17, iron-56, 25 magnesium- Indicate the number of protons, electrons, and neutrons for the elements above. O: Fe: Mg: F. ISOTOPES: Atoms of the same element that have different masses (different number of neutrons, same number of protons). 1. All elements have 2 or more isotopes. The atomic mass is the average of all the different isotopes. It is not a simple average. The average takes into account the percentage of occurrence of the isotopes considered. 2. Isotopes have different mass numbers but the same atomic number. 3. EX: protium, deuterium, and tritium 1 2 H 1 3 H 1 a. All have one proton and one electron. H 1 b. Protium has no (0) neutrons (99.985% of all H), deuterium has one neutron (0.015% of all H) and tritium has two neutrons (very small and very radioactive). V. AVOGADRO’S NUMBER ATOMIC MASS-the mass of an atom in amu’s (atomic mass units). EX: carbon = 12.0111 amu hydrogen = 1.007825 amu chlorine = 35.453 amu B. AVOGADRO’S NUMBER = 6.02 x 1023 atoms in WHAT? 1. You took the mass of 1 atom in amu’s and converted it to grams, then found that for every element there is the same number of atoms in that mass. 2. 1 dozen = 12 1 case = 24 1 mole = 6.02 x 1023 atoms [Instead of saying, “Give me a dozen eggs, the chemist says, “Give me a mole of carbon.] VI. MOLE = THE AMOUNT OF A SUBSTANCE THAT CONTAINS 6.02 x 1023 OF ANY KIND OF CHEMICAL UNIT ( atoms, molecules, ions). A. MOLAR MASS- the mass in grams of one mole of naturally occurring atoms of an element. Its unit is grams/mole (g/mol). 1. EX. Give the molar mass of: Fluorine______________, Magnesium_____________, Silver_____________ 2. Give the grams in one mole of: Fluorine______________, Magnesium_____________, Silver_____________ 3. Give the number of atoms in one mole of: Fluorine______________, Magnesium_____________, Silver_____________ 4. If you have 18.998 grams of fluorine, how many moles is this? 5. If you have 48.610 grams of magnesium, how many moles is this? VII. MOLE PROBLEMS: Use the “canceling units” method. A. START WITH WHAT IS GIVEN (INCLUDING UNITS) AND TRY TO END UP WITH WHAT YOU WANT (INCLUDING UNITS). Space has been left you to complete the problems. Use these conversions. 1 mole of an element element the molar mass of the element 1 mole of an element 6.02 x 10 23 atoms the molar mass of the 1mole of an element 6.02 x 10 23 atoms 1 mole of an element 1. What is the mass of 3.50 moles of copper? 2. What is the mass of 5.75 moles of copper? 3. How many moles are there in 6.195 grams of phosphorus? 4. How many moles are there in 0.0400 grams of copper? ***check answers to make sure your resulting unit is correct!! B. One and/or two step problems 1. How many atoms are in 36.0 grams of carbon? 2. How many grams are in 1.90 x 10 24 atoms of copper? How many moles are in 1.90 x 10 24 atoms of copper? 4. How many atoms are in 245.0 grams of gold? ***Are units included in your work? Do the units cancel? Are there units in your answer? If the answer to any of these is NO, go back and include them!! SIGNIFICANT FIGURES A measurement can only be as accurate and precise as the instrument that is used for measuring. A scientist needs to understand and document the accuracy of a number, not just the set of numbers. The accuracy of a number can be determined by looking at the number of significant figures that it contains. There are three rules to determine the significant figures in a number. 1. If an answer starts with a digit 1-9 and has a decimal point anywhere within the number, all figures are significant. 2. If an answer starts with a zero and decimal point, look to the first digit 1-9. That digit and all digits that follow (including zeros) are significant. 3. If an answer starts with a digit 1-9 and does not have a decimal point, all digits are significant unless the answer ends in zeros. Then all digits are significant except the last zero(s). I. Determine the number of significant figures in the following set of numbers and state which rule applies. 1. 0.04 _____ _____ 2. 6,000. _____ _____ 3. 0.050 _____ _____ 4. 3,042.00 _____ _____ 5. 205 _____ _____ 6. 0.0008 _____ _____ 7. 205.0 _____ _____ 8. 0.3010 _____ _____ 9. 6,000 _____ _____ 10. 20,002 _____ _____ 11. 7030 _____ _____ 12. 80,200 _____ _____ 13. 0.400 _____ _____ 14. 4.7 x 108 _____ _____ 15. 788.5 _____ _____ 16. 20,300,000. _____ _____ 17. 0.090200_____ _____ 18. 2.000 x 104 _____ _____ 19. 0.000420_____ _____ 20. 2.04 x 10 20 _____ _____ Significant Figures with addition, subtraction, multiplication and division If the question involves addition or subtraction, line the columns up so the decimal points are in alignment. The data with the least number of decimal points decides the number of decimal points in the answer. 9.985 The datum with the least number of decimal points is 11.0, therefore the 10.05 answer can only have one decimal point, because the least accurate number, 11.0 11.0, has only one decimal point. The answer would be rounded to 31.0. 31.035 When multiplying or dividing data, the answer contains the same number of sig figs as the datum with the least number of sig figs. 35.0 x 32.75 x 28 = 32095 because 28 has 100.35 100.35 = 319.8305929 = 3.2 x 102 2 sig figs 2 sig figs. Add or subtract the following sets of data: 1.005 + 1.253 + 1.14 = _____________ 0.04560 + 0.0325 + 0.26 = ____________ 3.9 – 2.803 = _____________ 249.035 248.98 = _____________ Multiply or divide the following sets of data: 37.0970 x 2.09 = ___________________ ______________ 28.605 x 2.00 x 0.0004560 0.002480 0.000470 = = _____________ 3.0 MATTER, ATOMS, MOLES ASSIGNMENT-UNIT 2 I. Isotopes: A. What is an isotope?________________________________________________ _____________________________________________________________ __ _____________________________________________________________ __ B. For 235U, determine: Number of protons______electrons______neutrons_____ 92 C. For 238U, determine: Number of protons______electrons______neutrons_____ 92 D. Are B and C isotopes? Why or why not? ______________________________ _____________________________________________________________ ___ _____________________________________________________________ ___ II. Define: A. molar mass:______________________________________________________ _____________________________________________________________ ___ B. mass number:____________________________________________________ _____________________________________________________________ ___ C. atomic mass: _____________________________________________________ _____________________________________________________________ ___ D. atomic number:___________________________________________________ _____________________________________________________________ ___ III. Using a periodic table, determine: A. number of protons in F_________ Ar_________ C. number of neutrons in He_______ Fe______________ E. atomic number of Zn___________ Cl_________ G. number of neutrons in Pt________ Ni________________ IV. Three isotopes of carbon are: 12 6 C B. number of electrons in D. mass number of F. atomic mass number of H. molar mass of 13 6 C 14 C 6 A. They are the same in that:___________________________________________ _____________________________________________________________ ___ B. They are different in that: ___________________________________________ _____________________________________________________________ __ V. Suggest a way to separate the following mixtures: A. salt dissolved in water_____________________________________________ _____________________________________________________________ __ B. sugar and powdered glass___________________________________________ _____________________________________________________________ __ C. alcohol and water_________________________________________________ _____________________________________________________________ __ D. pieces of iron and wood____________________________________________ _____________________________________________________________ __ VI. Classify the following as elements (E), compounds (C), homogeneous mixtures (S) or heterogeneous mixtures (HM). _____1. CH3OH _____11. table salt (NaCl) _____2. CaCO3 _____12. copper _____3. C8 H16 _____13. sugar water _____4. oxygen _____14. raisin bread _____5. vitamin C _____15. wood _____6. dry ice (CO2 ) _____16. sulfur dioxide (SO2) _____7. hamburger _____17. milk _____8. after-shave lotion _____18. mercury _____9. aluminum foil _____19. smog _____10. iron nail _____20. clear sea water # elements_________ mixtures________ # of compounds________ # of VII. Does the law of definite composition apply to mixtures? Why or why not? _____________________________________________________________ _ _____________________________________________________________ __ VIII. Classify the following as physical property (P) or chemical property (C). _____1. blue color _____9. reacts with water to form a gas _____2. density ____10. reacts with a base to form a precipitate _____3. flammability ____11. hardness _____4. solubility ____12. boiling point _____5. can neutralize a base ____13. reacts with acid to form hydrogen gas _____6. supports combustion ____14. luster _____7. tastes sour ____15. stinks _____8. melting point ____16. malleability IX. Classify the following as a physical change (P) or chemical change (C). _____1. wood rotting _____9. pH changes _____2. ice melting ____10. bromothymol blue changes to yellow _____3. evaporation ____11. baking soda and vinegar reacts _____4. milk sours ____12. salt dissolves in water _____5. rain ____13. pepper suspended in water _____6. water changing to steam ____14. crushing an Alka Seltzer tablet _____7. sugar changing to caramel ____15. Alka Seltzer tablet dropped in water _____8. iron rusts ____16. metal is pulled into a wire X. Mole problems-show all work including units for credit. Use canceling units method. 1. How many moles are in 0.7500 grams of sodium? 2. How many grams are in 2.50 moles of gold? 3. How many grams are in 1.80 x 1023 atoms of silver? 4. How many moles are in 4.50 x 1015 atoms of silicon? 5. Indicate the number of moles in 24.50 grams of chlorine. 6. What is the mass in grams of 0.500 moles of magnesium? 7. How many atoms are in 3.00 moles of tungsten? 8. How many moles are in 4.10 x 1021 atoms of platinum? 9. How many atoms are in 10.00 moles of potassium? 10. How many moles are in 0.150 grams of aluminum? 11. How many grams are in 5.00 x 1025 atoms of helium? 12. How many atoms are in 45.00 grams of cobalt? 13. How many atoms are in 3.50 grams of hydrogen? 14. How many moles are in 0.56 grams of boron? 15. How many grams are 5.00 moles of arsenic? 16. How many atoms are in 5.00 moles of phosphorus? 17. How many atoms are in 76.4 grams of iron? 18. How many grams are 0.083 moles of helium? 19. How many atoms are in 3.20 moles of lithium? 20. How many grams are in 3.10 x 1011 atoms of chlorine? 21. How many moles are in 0.152 grams of zinc? 22. How many atoms are in 2.00 moles of gallium? 23. How many atoms are in 76.4 grams of iron? 24. How many moles are in 12.2 grams of tungsten? 25. What is the mass in grams of 5.0 moles of magnesium? 26. How many moles are in 3.7 x 10 23 atoms of sodium? 27. How many atoms are in 10.0 moles of platinum? 28. How many moles are in 0.152 grams of gold? 29. How many atoms are in 4.8 grams of cobalt?