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Chapter 5

Chapter 5. Atomic Structure and The Periodic Table. Unit 2. For Advanced Chemistry… This starts Unit 2, which will cover Chapter 5 and Chapter 28. Unit 3 will cover Chapters 13 and 14 for those who like planning ahead. For Chemistry…

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Chapter 5

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  1. Chapter 5 Atomic Structure and The Periodic Table

  2. Unit 2 • For Advanced Chemistry… • This starts Unit 2, which will cover Chapter 5 and Chapter 28. • Unit 3 will cover Chapters 13 and 14 for those who like planning ahead. • For Chemistry… • You are going to do Chapter 5 totally, but only selected topics in Chapters 28, 13, and 14

  3. Objective Ahttp://sunsite.berkeley.edu/CalHistory/photos-large/seaborg.big.jpg Glenn T. Seaborg • A tour down memory lane from about 400 BC to the early 1900s… • For a quick recap on a lot of the amazingly important discoveries that brought chemistry from the land of con-men practicing mere magic tricks to the Central Science that it has become, see… • Chemical History PowerPoint, available in Unit 2 on the website. Discovered Plutonium in 1940; won Nobel Prize in 1951; had dinner with Mr. Schwartz in 1981; element 106 named in his honor in 1997 (Sg); died 1999.

  4. Objective B: Just how small is an atom?http://imagecache5.art.com/p/LRG/6/667/USYC000Z/fedex-field--washington-d-c-.jpg • Has anyone been to a professional football stadium or a major college football stadium? • If the nucleus of an atom was the size of a marble, sitting at the 50 yard line, the electrons would be about the size of really little gnats (bugs) whizzing around the top rows of the upper deck. So then, most of the atom is just “empty space.”

  5. Objective B: Just how small is an atom?http://kara.allthingsd.com/files/2009/04/penny.jpeg • Let’s use a penny as an example (picture, in slide show, is approximately life-size). A penny, if made of pure Cu (copper) would have 2.4 x 1022 atoms. That’s 24,000,000,000,000,000,000,000 atoms, btw. • If you lined up 100,000,000 atoms, they would make up a line of approximately 1 cm. So, 2.4 x 1022 atoms, if lined up would make a line that was approximately 2.4 x 109 KILOMETERS long. Approx. 1 cm from arrow to arrow (in slide show mode)

  6. How far is that?http://stardate.org/images/gallery/sun5.jpghttp://1.bp.blogspot.com/_Clz-U8TjA_0/SYQUNjRgeRI/AAAAAAAAAAU/kcQOn18_eP4/s320/EarthBlueMarbleWestTerra.jpg • 2.4 x 109 KILOMETERS is 8 trips from the Earth to the Sun and back. • By the way, it takes just over 25 pennies (25.08) to make a mole of Cu. That’s 63.5 grams of pennies. • Scanning tunneling microscopes are capable of seeing the surface of individual atoms. This is a relatively new development, within the past 20 years or so. Those didn’t exist when I was in high school or college.

  7. Angstoms (Å)http://intro.chem.okstate.edu/1314F00/Lecture/Chapter7/ATRADIID.DIR_PICT0003.gif • Even the largest atoms are very small. The diameter of a uranium atom is only about 0.345 nanometers. • A special unit is sometimes used to describe atomic dimensions, such as atomic radius or atomic diameter. Note the trend as you go across a row and down a column. • That is the Angstrom. We use a Å to represent Angstroms (if you want to type that it’s shift-alt-A on a Mac and control-shift-2, shift-A on a bogus, inferior, Windows or Vista based machine).

  8. Angstoms (Å)http://upload.wikimedia.org/wikipedia/commons/1/11/Hydrogen_Atom.jpg • Even the largest atoms are very small. The diameter of a uranium atom is only about 0.345 nanometers. • 0.345 nm = 3.45Å • 1nm = 10Å • 1Å = 1 x 10-10 meters • A hydrogen atom is the smallest atom. H has a diameter of only 0.74Å. About 13.5 billion hydrogen atoms could fit onto the edge of a meter stick.  Isotopes 

  9. What does an atom look like?http://www.lanl.gov/orgs/pa/newsbulletin/images/Isotopes_logo.jpg • In your notes, draw a simple picture of an atom. How about Lithium. • What did you draw? AAA baseball club Albuquerque Isotopes logo (you need to know what isotopes are!)

  10. Atomshttp://upload.wikimedia.org/wikipedia/commons/thumb/e/e1/Stylised_Lithium_Atom.svg/270px-Stylised_Lithium_Atom.svg.pnghttp://www.solarsystempictures.net/Atomshttp://upload.wikimedia.org/wikipedia/commons/thumb/e/e1/Stylised_Lithium_Atom.svg/270px-Stylised_Lithium_Atom.svg.pnghttp://www.solarsystempictures.net/ Neutron Proton Electron • Most people probably drew a nucleus of some type with electrons orbiting around it. • Possibly it looks a little like a mini solar system. • Atoms are composed of • Protons • Neutrons • Electrons Lithium Planets=Electrons Sun=Nucleus

  11. Subatomic Particles

  12. Electrons • Electrons were the first particle discovered. • JJ Thompson discovered the electron using cathode ray tubes, and modified the model of the atom because of this discovery. • The electron has a very small mass. It is actually 1/1840th the size of a proton (0.00054 times). In other words, if an electron was a smidge over a pound, protons and neutrons would weigh almost a TON.

  13. Electronshttp://educar.sc.usp.br/licenciatura/2003/mi/Millikan-Oil-Drop-Apparatus.gifElectronshttp://educar.sc.usp.br/licenciatura/2003/mi/Millikan-Oil-Drop-Apparatus.gif Robert Millikan measured the charge of the electron in “The Oil Drop Experiments” • Since it’s so small relative to a proton, we say that it has a relative mass of 0. • Electrons are negatively charged. Each electron has a charge of -1. (Don’t forget the negative…it’s important!) • If an atom loses an electron, what remains will have a positive charge. If an atom gains an electron, it will have a negative charge. This is what he used to do it…

  14. Protonshttp://web.buddyproject.org/web017/web017/images/atom.JPGProtonshttp://web.buddyproject.org/web017/web017/images/atom.JPG • Protons were the next subatomic particle to be discovered. • Protons were discovered by E. Goldstein. • Protons have a relative mass of 1 and a charge of +1.

  15. Protonshttp://www.periodictable.com/Items/020.6/index.html Atomic Number • Protons determine the “identity” of an atom. The number of protons is a property called “atomic number.” Atomic numbers are on the periodic table. • The number of protons determines what kind of atom it is. • H has 1 proton • C has 6 protons • U has 92 protons

  16. Protons • Neutral atoms have the same number of protons and electrons. (Makes sense, right?) • The charges balance each other out. (Ca has 20 protons, and must have 20 negatively-charged electrons to balance out those positive charges) • Protons are located in the nucleus of the atom. (Where are the electrons?)

  17. Neutronshttp://www.ct.infn.it/~rivel/Archivio/chadwick.jpghttp://kwisp.files.wordpress.com/2009/05/adventures-jimmy-neutron-300-032707.jpgNeutronshttp://www.ct.infn.it/~rivel/Archivio/chadwick.jpghttp://kwisp.files.wordpress.com/2009/05/adventures-jimmy-neutron-300-032707.jpg • Neutrons are also located in the nucleus of the atom. • The nucleus was discovered by Ernest Rutherford, a former student of JJ Thompson. • The neutron was the last particle discovered, by James Chadwick, a former student of Rutherford. Ooops, wrong neutron! Chadwick

  18. Neutrons • More than likely, the fact that neutrons had no charge made it harder to discover. • The neutron has a relative mass of 1, the same as a proton. However, it has no charge. Therefore, we say that the charge = 0. • The actual mass of a neutron is almost the same as that of a proton. It is slightly different • P = 0.0000000000000000000000016726 g • N = 0.0000000000000000000000016749 g

  19. Golf Balls In BeakersMy Little Model of the Atomhttp://www.vias.org/physics/bk4_03_02.html • These are in the lab somewhere. Find them. • The pink balls represent protons. • The white balls represent neutrons. • Scientists quickly figured out by experimentation how many protons each element had. If you want to read more, check out the link above. Basically though….

  20. Golf Balls In Beakers • They were able to ionize (remove electrons—all of them) and found that • Hydrogen had 1 proton. They figured this out because they were able to make H+ but not H2+ • Helium had 2 protons. Again, they were able to make He+ and He2+ BUT NOT He3+ • Lithium had 3 protons. • Magnesium had 12 protons. • Bromine had 35 protons. • Uranium had 92 protons. For the heavier elements, they were not able to remove all of the electrons. They had to do other experiments to figure that out, using a ratio of a known atomic number and an unknown one.

  21. Golf Balls In Beakers • Not all the calculations were accurate at first, but they figured them out in time. • Scientists also knew what the masses of the elements were, and the numbers weren’t adding up. • Hydrogen was OK. It seemed to work out. • But helium should weigh twice as much as hydrogen. And lithium should weigh three times as much. And carbon should weigh 6 times as much.

  22. Golf Balls In Beakers • But they didn’t. • Helium was actually 4 times as heavy as hydrogen. Lithium was 7 times as heavy. Carbon was 12 times as heavy. • And that was very confusing. However, the neutron provided the final piece of the puzzle. The neutrons accounted for the missing mass.

  23. Neutrons • It turns out that Helium has 2 protons AND 2 neutrons, which makes it 4 times as heavy as hydrogen. • Lithium has 3 protons and 4 neutrons, which makes it 7 times as heavy as hydrogen. • Carbon has 6 protons and 6 neutrons, which makes it 12 times as heavy as hydrogen. • The numbers added up.

  24. The Nucleushttp://www.chemicalelements.com/bohr/b0019.gif • Since the neutrons are located in the nucleus, with the protons, substantially ALL of the mass of the atom is contained within the nucleus. • Mass of nucleus in diagram 0.0000000000000000000000651 g • Mass of electrons 0.0000000000000000000000000173 g • In other words, if the nucleus weighed 651 pounds, the electrons (combined) would weigh less than a McD’s quarter-pounder patty. What element is this??

  25. Strong Nuclear Force • But positively charged things repel other positively charged things, right? • Why do all the protons stick together in the nucleus? • Why doesn’t it just spontaneously break apart?

  26. Strong Nuclear Forcehttp://www.antonine-education.co.uk/Physics_AS/Module_1/Topic_5/strong_force.jpg • The answer is strong nuclear force. • It’s the strongest known force in the universe. It far, far stronger than gravity. • It only can be felt when the particles are extremely close together, like when they are packed together in the nucleus. • Protons and neutrons are made of quarks. It’s thought that the quarks attract other quarks and hold the nucleus together, even though all of the protons are positively charged and would otherwise repel each other. The secret’s in the attractions between the quarks…

  27. Objective Dhttp://www.fiu.edu/~zhangj/cartoon_quantum3.gif • Scientists, starting with Dalton, came up with models of the atom, to help understand it and help to predict its behavior. • Check out the Chemical History power point for more details as the model evolved over about 130 years from Dalton to Quantum Mechanics.

  28. Objective E • We already know that the number of protons is what makes an atom unique. • Hydrogen has 1 proton. • Carbon has 6 protons. • Uranium has 92 protons. • The “atomic number” is the number of protons. We sometimes use a Z to represent atomic number. So, if “ProtonMan” was a superhero, he’d have a “Z” on his suit??

  29. Objective E • So, for hydrogen, Z = 1 • For carbon, Z = 6 • For uranium, Z = 92. • What is the atomic number for • Aluminum • Zinc • Chlorine Don’t memorize these…they are on the Periodic Table Find THEM!!

  30. Objective F • So, Z (atomic number) tells us how many protons an atom has.It does NOT tell you how many ELECTRONS you have (accurately) all the time! • Most atoms have no charge. That means that the number of protons (which are positively charged) must balance out the number of electrons (which are negatively charged).

  31. Objective F • Unless you are TOLD that the atom has a charge, you should assume it has no charge, and therefore, # of protons = # of electrons. • Hydrogen (Z = 1) also has one electron. • Lithium (Z = 3) also has 3 electrons. • Carbon (Z = 6) also has 6 electrons. • Uranium (Z =92) also has 92 electrons. • BUT REMEMBER The numbers of protons doesn’t always equal the numbers of electrons.

  32. Objective F • Some atoms can lose electrons. When they do so, they will form a positive “ion.” Some atoms can gain electrons. When they do so, they will form a negative “ion.” • An ion is a atom which has an electrical charge (either positive or negative). We’ll get to those in Chapter 6. Na+1 and Cl-1 are formulas for ions. • The number of protons cannot change. If the number of protons changes, it’s no longer the same element. Atoms can gain or lose electrons, but they can NOT gain or lose protons in any chemical reaction.

  33. Schwartz’s Law(a law I made up…hey, it’s my class) • To calculate the number of electrons, use • # of Electrons = Z – IC • Where Z = atomic number and IC = ionic charge. • Ex: Suppose we have a sodium ion with a + 1 charge. How many electrons does it have? Atomic number (Z) is 11 (find this on Periodic Table) and ionic charge is 1. • # electrons = 11 - 1 = 10

  34. Schwartz’s Law • Let’s calculate a couple more… • Ex: Suppose we have a sulfur ion with a - 2 charge. How many electrons does it have? Atomic number (Z) is 16 and ionic charge is -2. • # electrons = 16 - (-2) = 16 + 2 = 18 • Ex: Suppose we have an zinc atom with no charge. How many electrons does it have? Atomic number (Z) is 30 and ionic charge is 0. • # electrons = 30 - 0 = 30

  35. Objective Fhttp://www.atomicarchive.com/Physics/Images/isotopes.jpg 6 neutrons 8 neutrons • How do we calculate how many neutrons we have? • In order to do that, we need to look at another property, called atomic mass. The atomic mass of an atom = THE SUM of protons and neutrons. • We will use another formula • # Neutrons = A – Z • A = Mass Number • So, what is Z again? Hey these are isotopes again. Isotope = same # of protons but a different # of neutrons.

  36. Objective Fhttp://www.lbl.gov/abc/Basic.html#Nuclearstructure • Let’s look at an example. An atom of Bromine (Br-80) has Z = 35 and Mass Number = 80. How many neutrons does it have? (Br-80 doesn’t mean bromine with a charge of -80. When they write it like that, it’s a DASH and 80 is the mass number) • # Neutrons = Mass Number - Atomic Number • # Neutrons = 80 - 35 = 45

  37. Objective F Special note Isotopes of hydrogen: 1H = hydrogen 1 proton, 0 neutron 2H = deuterium 1 proton, 1 neutron 3H = tritium 1 proton, 2 neutrons Hydrogen is the only element with special names for isotopes. • An atom of Deuterium has Z = 1, and Mass Number = 2. How many neutrons does it have? • Since Z = 1, deuterium must be some type of hydrogen. Hydrogen has Z = 1, and since every element has a unique number of protons, no two elements can have the same number of protons. • Deuterium is a form of hydrogen. When deuterium reacts with oxygen it forms something called “heavy water.” Heavy water is represented with the formula D2O. • # of Neutrons = Mass Number - Z = 2 - 1 = 1

  38. Power Point Assignment • Pick an element…any element… • Well, not just any element. Pick an element whose symbol begins with the same letter as your first name. • If for some strange reason none exists, say for instance your name is Julie or Joe (sorry, no J elements) than use the next letter. • So Julie could pick Uranium • And Joe could pick Osmium • Research your element and write a 150 word summary on what you learned.

  39. Objective Ghttp://www.usagold.com/images/gold-coins-images.jpeghttp://finestimaginary.com/shop/images/medium/jewellery/au_MED.jpg • How do isotopes differ from each other? (You should know this by now). • Look at gold (Au) on the periodic table. It says that the mass = 196.967. Since mass number and atomic number are ALWAYS whole numbers, how do we get .967? • The answer is that the atomic masses on the periodic table are averages.

  40. Objective G • They get that average atomic mass for Au by taking into account ALL of gold’s isotopes. • Isotopes differ from each other in the number of neutrons. They behave the same CHEMICALLY because all isotopes of the same element have the same number of protons. • The study guide talks about water and heavy water. Heavy water is the same as water, except that instead of H-1 it is formed using H-2, which is sometimes called deuterium. So while water has a molar mass of 18, deuterium oxide or heavy water has a mass of 20 (2 + 2 + 16)

  41. Objective Ghttp://www.damninteresting.net/content/heavy_water_ice.jpg • Here’s an interesting fact… • Ice cubes made out of “heavy water” will not float. They sink to the bottom. So it has different physical properties. • Although it PROBABLY tastes the same, you should NOT drink it though. Too much of it can really mess up your system.

  42. Objective G Don’t drink the HEAVY water! • You can purchase D2O. For $33 (for 2 ounces), you can purchase some from a company to be used as a “hydrating product” for your skin. It’s enriched with deuterium (meaning it has more in it than just normal water). It’s doubtful, in my opinion, that it does anything special, but if you have a different hypothesis, and $33 to burn, there’s a link in your study guide. • You can also purchase very pure heavy water as a scientific reagent. We call that deuterium oxide, because a real chemist would never order something that was called “heavy water.” It sells for $330 for 250g (which is about 2/3 of a can of soda). This stuff has been scientifically analyzed to contain 99.8% (at least) of D2O, which is why it’s a lot more expensive than the “hydrating product” for your skin.

  43. Objective H Math Alert • How do we calculate the average atomic mass? • To do so, you need to know 2 things: • All possible isotopes for an element • The percent abundance for each (in other words, how much of the whole is represented by each isotope).

  44. Objective H • Let’s look at an example: • Chlorine has 2 isotopes • 35Cl which is 75.77% of the total amount of chlorine. • 37Cl which is 24.23% of the total amount of chlorine. • What is the average atomic mass of Chlorine?

  45. Objective H • Cl-35 accounts for 75.77% of the total chlorine. CL-37 accounts for the rest. • Remember to convert percents into decimals, you have to move the decimal point 2 places to the left. • You then mutiply the percentage (in decimal form) times the mass number for that isotope. You do that for the other isotope too, and then add the answers together. • Avg Atomic Mass = 35 (0.7577) + 37 (0.2423). • Avg Atomic Mass = 26.52 + 8.97 = 35.49

  46. Objective H • In our class, we are always going to round average atomic masses to 1 decimal place. • So, we’ll round 35.49 to 35.5 and that’s the average atomic mass of Chlorine that we’ll use. • Why can’t you just average 35 and 37 (the two isotopes) and get 36 as the average atomic mass? Why is that wrong?

  47. The Periodic Table • We’ve described the Periodic Table as • The biggest cheat sheet in science • The best tool we have in Chemistry • Your best friend on the test • Suppose we didn’t have a Periodic Table. You would have to memorize every fact about every element.

  48. This is a map…

  49. What does it tell you? • It shows you the states. If you know approximately where Virginia is, you can easily find it on the map. • It shows you state abbreviations. If you don’t know where Virginia is, or even what it sort of looks like, you can find it by using the abbreviation “VA.” • It shows you data for each state… • The name of the state capital. • The approximate location of the state capital • What other states are above, below or next to each state. • The sizes of the states..which are large and which are smaller.

  50. What else does it tell you?http://www.destination360.com/maps/virginia-map.gif • Well, that’s about all, really. • But you can make some assumptions about the states based on their position on the map. • For example, VA borders NC, MD, TN, WV and KY. You might assume that VA has some things in common with each of these states. • You would be right.

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