Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
History of the Atom In Atomic Theory, if we were to zoom in on a copper wire, it might look like the picture below. What is between the atoms? What did be believe before we thought there were atoms? We thought matter was continuous, not made of little particles What would it have looked like? Why would we have believed matter was continuous? Because it looks like it. Why don’t you see atoms when you look at a piece of copper wire? Because atoms are sooooooo small. How big is an atom? If a baseball was blown up to the size of the earth. An atom would be about the size of a baseball. Picture yourself out in space trying to see someone holding a baseball in your backyard. We could never hope to see an atom with visible light Atom We can “see” them with special microscope called a scanning tunneling electron microscope. Guess who the first to do this was? Atoms were first proposed by 2,400 years ago by the Greek philosopher Democritus BUT the idea did not catch on until 2,200 years later. Why did no one believe him? Philosopher did not experiment, they just thought. NO PROOF. If we can’t see atoms why do we believe in them now? (even well before the SEM) John Dalton (1766-1844) • English School teacher and early meteorologist • Trying to learn what caused rain and where it came from • Discovered that the water actually came out of the air itself • Combined the concept of atoms with that of elements • His conclusion came from several experiments. (not just guessing) How could water be in air? If matter is continuous, then there is no room in air for water. Air Water Air & water mixed?? How can two things occupy the same space?? Atomic theory of matter Air Water Air & water mixed The molecules of air and water can mix because they do not occupy the same space Experiments also showed that: A given compound (say NaCl) had the same % of elements, no matter where he located it from. (ocean water or made from Na & Cl) Always 1 Na & 1 Cl by mass 39% Na & 61% Cl Formation of NaCl from its elements http://www.youtube.com/watch?v=2mzDwgyk6QM Why should a compound have an exact % of elements According the the continuous theory of matter I can mix any amount of Na and Cl Na Na Cl NaCl Cl NaCl atomic theory of matter: atoms of Na react with atoms of Chlorine to form a compound Cl Na + Na Cl + + Cl Na Can part of a Na atom react? Na Cl Na Law of definite composition: a sample of a given compound will have the same composition of elements no matter where it was obtained. The composition is often expressed as % mass. Acetic acid (active ingredient in vinegar) C2H3O2 Can be made by fermenting fruit or by chemical reactions with Crude Oil. Both are used as food ingredients. Same compound 2C : 3H : 2O By mass this is 49% C : 1% H : 50% O • The law of definite composition: A compound has the same composition whether you find it here or on the other side of the world, whether you find it in nature or if you synthesize the compound. Composition of iron sulfide Law of Multiple Proportions CO2 CO A law proposed by Dalton which states that when elements combine, they do so in the ratio of small whole numbers. For example carbon and oxygen react to form CO or CO2, but not CO1.8 Law of multiple proportion: when the same elements combine to form different compounds they do so in whole number ratios. Compounds with Hydrogen and Oxygen Mass H (g) Compound A Compound B .125 g .250 g Mass O (g) 1.00 g 1.00 g What do you notice about this??? Why should there be whole numbers involved? Because of atoms!!! Compound A Compound B O O H H H2O 2H:1O O H H H2O2 1H:1O There is EXACTLY twice as much Oxygen in compound B Law of Conservation of Mass Massreactants = massproducts If chemical reactions are rearrangements of atoms, then mass would be conserved: If atoms are rearranged, and not created or destroyed, then the mass of the reactants must equal the mass of the products. Reactants Products Atoms are conserved. • In natural processes, atoms are not destroyed; they are recycled. online Dalton’s Atomic Theory 1.) All matter is made of tiny indivisible particles called atoms. 2.) Atoms of the same element are identical, atoms of different elements are different. 3.) Atoms of different elements combine in whole number ratios to form compounds. 4.) Chemical reactions occur when atoms are separated, joined or rearranged Is Dalton right on everything????? Chemical reactions occur when atoms are separated joined rearranged + + • Bill Nye Atomic Theory Subatomic Parts Parts of Atoms • J. J. Thompson - English physicist. 1897 • Made a piece of equipment called a cathode ray tube. • It is a vacuum tube - all the air has been pumped out. Thomson’s Experiment Voltage source - + Vacuum tube Metal Disks Thomson’s Experiment Voltage source - + Thomson’s Experiment Voltage source - + Thomson’s Experiment Voltage source - + Thomson’s Experiment Voltage source - + Passing an electric current makes a beam appear to move from the negative to the positive end Thomson’s Experiment Voltage source - + Passing an electric current makes a beam appear to move from the negative to the positive end Thomson’s Experiment Voltage source - + Passing an electric current makes a beam appear to move from the negative to the positive end Thomson’s Experiment Voltage source - + Passing an electric current makes a beam appear to move from the negative to the positive end Thomson’s Experiment Voltage source • By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field he found the beam was negative and that it was not just light. (light is not affected by a magnet or electric field) Thomson’s Experiment Voltage source + By adding an electric field he found the beam was negative and that it was not just light. (light is not affected by a magnet or electric field) Thomson’s Experiment Voltage source + By adding a paddlewheel Thomson’s Experiment Voltage source + He added a paddlewheel Thomson’s Experiment Voltage source + He added a paddlewheel and saw that the beam turned it. Thomson’s Experiment Voltage source + He added a paddlewheel and saw that the beam turned it. Thomson’s Experiment Voltage source + He added a paddlewheel and saw that the beam turned it. Thomson’s Experiment Voltage source + He added a paddlewheel and saw that the beam turned it. Thomson’s Experiment Voltage source + Since the beam turned the paddlewheel, He concluded that: the beam had mass and was likely composed of particles. Experiments were repeated with many different gases and all found the same resulting beam of negative particles. The conclusion was that all atoms have these negative particles in them. It was later called the electron, but at the time Thomson called them "corpuscles”. By using the cathode ray tube and an electric field. The deflection of the electron beam gave the charge to mass ratio of a electron. Voltage source + - Charge of an electron? 1.7588028 1011 coulombs/kg = mass of an electron? If one of the missing numbers could be found then both would be known Robert Millikan in 1909 set out to find the charge on 1 electron, in one of the most clever experiments to date. Education Millikan received a Bachelor's degree in the classics from Oberlin College in 1891 and his doctorate in physics from Columbia University in 1895 – he was the first to earn a Ph.D. from that department. – "At the close of my sophomore year [...] my Greek professor [...] asked me to teach the course in elementary physics in the preparatory department during the next year. To my reply that I did not know any physics at all, his answer was, 'Anyone who can do well in my Greek can teach physics.' 'All right,' said I, 'you will have to take the consequences, but I will try and see what I can do with it.' Millikan Oil Drop movie http://chemistry.umeche.maine.edu/~amar/fall2007/Millikan.html .2 e- .4 .3 e- ee- ee- e- e- e- He looked at the charges on the oil drops and found that they were different by whole numbers. The smallest amount the charge changed was the charge of 1 electron He found that an electron has a mass of: 9.11 x 10-28 g how “heavy” is that? .0000000000000000000000000000911 g If all atoms have these negative particles in them, why isn’t everything electrically charged? Why don’t I get shocked when I touch everything?? Atoms have a neutral charge because of… Protons So atoms have negative particles called electrons and some positive stuff (we don’t know about protons yet in 1909) How does this fit together to make an atom? The first accepted idea came from J.J. Thomson It was referred to as the Plum Pudding Model electrons Positive charge smear But then new evidence came to light courtesy of Lord Ernest Rutherford Rutherford’s experiment • Ernest Rutherford -English physicist. (1910) • Believed in the plum pudding model of the atom • Wanted to see how big they are. • Used radioactivity. • Alpha particles - positively charged pieces- helium atoms minus electrons • Shot them at gold foil which can be made a few atoms thick. Rutherford’s experiment • When an alpha particle hits a fluorescent screen, it glows. • Here’s what it looked like Lead block Uranium Fluorescent Screen Gold Foil He Expected • The alpha particles to pass through without changing direction very much. • Because…? • …the positive charges were thought to be spread out evenly. Alone they were not enough to stop the alpha particles. What he expected Because He thought the mass was evenly distributed in the atom Since he thought the mass was evenly distributed in the atom What he got How he explained it • Atom is mostly empty. • Small dense, positive piece at center. • Alpha particles are deflected by it if they get close enough. + + Density and the Atom • Since most of the particles went through, it was mostly empty space. • Because the pieces turned so much, the positive pieces were heavy. • Small volume, big mass, big density. • This small dense positive area is the nucleus. Rutherford Gold foil experiment movie Bill Nye’s Greatest Discoveries • Atomic Theory • The electron Size of nucleus, electron Start at 4:25 G:\Documents\Chemistry RJ Main\Honors\Honors 08 Unit 4\The_Structure_of_the_Atom_and_Atomic_Spectra.asf World of Chemistry on-line video • The Atom - first 16 minutes Recreating Rutherford’s Experiment Each box has a hidden shape, Place a piece of paper on top roll a marble into the hidden area of the box Use a pencil to trace the marble’s path on the piece of paper Use the path and anything you hear to help determine the shape Repeat until you know what the hidden shape is NO PEEKING OR FEELING to find the hidden shape Turn in 3 pieces of paper stapled together with Names Containing marble paths your guess for the actual shape The shapes Other particles • Proton - positively charged pieces 1840 times heavier than the electron – by E. Goldstein • Neutron - no charge but the same mass as a proton – by J. Chadwick • Where are the pieces? Subatomic particles – p.111 Name Symbol Charge Relative mass (amu) Actual mass (g) Electron e- -1 1/1840 9.11 x 10-28 Proton p+ +1 1 1.67 x 10-24 Neutron n0 0 1 1.67 x 10-24 Atoms contain 3 particles e- + protons Charge neutrons electrons +1 0 -1 Mass 1 amu 1 amu .0005 amu Found nucleus nucleus outer shell If all atoms contain just protons, neutrons, and electrons how can atoms have different flavors??? Sulfur Lead Gold Bromine Neon Counting the Pieces • Atomic Number = number of protons in the nucleus • # of protons determines kind of atom (which element it is) • the same as the number of electrons in the neutral atom. • Mass Number = the number of protons + neutrons. • These account for most of mass If an atom has an atomic number of 5 that means it has 5 what? 5 protons If it also has an mass number of 11 that means it has 11 what? 11 (protons + neutrons) How many neutrons??? Mass # - Atomic # # neutrons 11 protons + neutrons - 5 protons 6 neutrons Symbols • Contain the symbol of the element (X), the mass number and the atomic number. If the atom is neutral then there is nothing here Mass number Atomic number X Symbols • Find the 9 – Atomic number 19 – Mass Number 9 – number of protons 10 – number of neutrons 9 – number of electrons 19 9 F Symbols Find the 35 –Atomic number 80 –Mass Number 35 –number of protons 45 –number of neutrons 35 –number of electrons 80 35 Br Symbols if a neutral atom has an atomic number of 34 and a mass number of 78 what is the 34 –number of protons 78 44 –number of neutrons 34 34 –number of electrons –Complete symbol Se Symbols if a neutral atom has 91 protons and 140 neutrons what is the 91 –Atomic number 231 –Mass number 231 91 –number of electrons 91 –Complete symbol Pa Symbols if a neutral atom has 78 electrons and 117 neutrons what is the 78 –number of protons 78 –Atomic number 195 195 –Mass number 78 –Complete symbol Pt Ions • If an atom does not have the same number of protons and electrons it has a charge • These charged atoms are called ions • The charge is usually indicated in the top right corner of the symbol 32 S 16 2- Does this ion have more protons or electrons?? Ions • If an atom has more electrons than protons it has a negative charge. • If an atom has more protons than electrons it has a positive charge Net Charge 1- –10 p+ and 11 e 2–12 p+ and 14 e 1+ –45 p+ and 44 e–150 p+ and 147 e- 3+ Symbol Atomic # Mass # 23 + 11 Na 36 - Cl 17 11 17 23 36 p+ 11 17 # particles in nucleus n0 e- 12 10 1+ 23 18 1- 36 19 Charge Isotopes • Dalton was wrong. • Atoms of the same element can have different numbers of neutrons. • different mass numbers. • called isotopes. • All elements have different isotopes. • Isotopes are not necessarily radioactive. But some are Naming Isotopes • Another way to name an isotope is to name the element, then the mass #. • carbon- 12 • carbon -14 • uranium-235 Comparing Isotopes atomic # mass # protons neutrons electrons • Carbon-12 • Carbon-14 6 12 6 6 6 6 14 6 8 6 Both carbon 12 and 14 behave the same in a chemical reactions. You have many carbon atoms in you. Carbon-12 is not radioactive but Carbon-14 is radioactive. Are you radioactive?? Other isotopes • Hydrogen-1 • Hydrogen-2 • Hydrogen-3 “normal hydrogen” deuterium tritium atomic # mass # protons neutrons electrons • Hydrogen-1 • Hydrogen-2 • Hydrogen-3 1 1 1 0 1 1 2 1 1 1 1 3 1 2 1 If we have ten marbles, and each marble weighs 1 g, what is the average mass of the marbles? 1g If we have two marbles, and one marble weighs 1 g and the other marble weighs 6g, what is the average mass of the marbles? 3.5 g If we have five marbles, and one marble weighs 6 g and the other four marbles weigh 1g, what is the average mass of the marbles? (6g x 1 marble) + (1g x 4 marbles) = 5 marbles 10 g 5 marbles If we have five marbles, and one marble weighs 6g and the other four marbles weigh 1g, what is the average mass of the marbles? (6g x 1 marble) + (1g x 4 marbles) = 2 g/marble 5 marbles Atomic mass • What is it and why is it a decimal. • Protons and neutrons both weigh 1 amu. (mass of electrons is almost nothing) • Chlorine’s atomic mass = 35.453 amu Does Chlorine have a half a proton or half a neutron??? Atomic Mass Most elements have more than 1 isotope in nature Protactinium-216 217 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 •Different isotopes have different masses because they have different #’s of _______ You need to gain some weight no + + no Hydrogen - 3 Hydrogen - 1 •Some of these isotopes are very rare. (partially because some isotopes are very unstable) Some isotopes will only last a fraction of a second •The atomic mass is an average based on the % abundance of these isotopes in nature If there are 10 boys and 20 girls in a room What is the % abundance of boys? 10 / 30 *100% = 33% Atomic Mass • Chlorine has two common isotopes 35 Cl 17 Isotope mass =34.9689 amu 37 Cl 17 Isotope mass =36.9659 amu • Notice that the actual mass (amu) of the isotope is very close to the mass number Atomic Mass 35 37 Cl 17 Isotope mass =34.9689 amu Cl 17 Isotope mass =36.9659 amu •If you were to go out and collect a sample of chlorine atoms (say in a bucket of chlorine bleach). You would find that there are some of each isotope. More specifically it is always: 75.77 % Cl-35 24.23 % Cl-37 No matter where you collected the sample, you would find that: 75.77 % are Cl-35 & 24.23 % are Cl-37 37 Cl 17 What is the average mass? 35 Cl 17 Finding the atomic mass % abundance as a decimal (34.9689 amu*.7577 + 36.9659 amu*.2423) 26.50 amu + 8.957 amu = 35.457 amu 37 Cl 17 Notice the atomic mass is “weighted” towards the more common isotopes 35 Cl 17 Atomic Mass • Is not a whole number because it is an average. • The atomic mass is closer to the mass of the most common isotope • BUT NO chlorine atoms have a mass of 35.45 because it is an average. If you have 1 marble that has a mass of 1 g and another that has a mass of 2 g. The average mass is 1.5 grams How many marbles have a mass of 1.5 grams? Copper has 2 Isotopes 63 29 62.93 amu Cu 65 29 64.93 amu Cu The atomic mass of copper is 63.546. Which isotope is more common? How many copper atoms have a mass of 63.546 amu? Carbon has 2 (primary) Isotopes 12 6 C 12.000 amu 13 6 C 13.003 amu The atomic mass of Carbon is 12.011 amu Which isotope is more common? How common is the other? Magnesium has 3 isotopes Mg-24 Mg-25 Mg-26 23.99 amu 24.99 amu 25.98 amu 78.9% abundant 10.0% abundant The rest What is the atomic mass of Mg? Mg-24 23.99 amu Mg-25 24.99 amu Mg-26 25.98 amu 23.99 amu *.789 + 78.9% 10.0% 11.1% Homework / Class work SHOW ALL WORK Gallium has 3 isotopes Isotope Isotope Mass Abundance Gallium-69 68.926 60.1% Gallium-71 70.924 The rest What is its atomic mass? Silicon has 3 isotopes Isotope Isotope Mass Abundance Silicon-28 27.98 amu 92.23% Silicon-29 28.98 amu 4.67% Silicon-30 29.97 amu remainder What is its atomic mass? It’s the number!! The atomic number is the number of protons. This is what determines the element. It is often listed on the bottom left of the symbol. The elements are listed in order of increasing atomic number. All atoms of helium have 2 protons How many protons does a nitrogen atom have. He 2 N Most atoms are electrically neutral. • If the atomic number of magnesium is 12. How many electrons does it have. Mg What 2 particles make 99.98% of the mass in an atom? • The mass number is the number of protons AND neutrons. • It is often indicated on the top left of the symbol Mass #- protons and neutrons 24 Mg 12 atomic #- protons # neutrons 12 Two ways to find the average mass Simple Average (34.969 amu + 36.966 amu) / 2 = 35.9677378 amu Does this average reflect how many of each isotope would be found in nature? A recipe 1 Scoop Potassium Iodide (KI) 5 mL Soap 10 mL H2O2 %H %O H2O 11% 89% H2O2 6% 94% Distinguishing Between Atoms • OBJECTIVES: – Explain how the atomic number identifies an element. Distinguishing Between Atoms • OBJECTIVES: – Use the atomic number and mass number of an element to find the numbers of protons, electrons, and neutrons. Distinguishing Between Atoms • OBJECTIVES: – Explain how isotopes differ, and why the atomic masses of elements are not whole numbers.