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Chapter 3 – Atomic Structure Atom - Greek for “Atomon” means“Indivisible” - Smallest unit that can exist alone or in combination with other atoms. Chapter 3 – Atomic Structure Atom - Greek for “Atomon” means“Indivisible” - Smallest unit that can exist alone or in combination with other atoms. Structure of an Atom … Things we know Two main areas of the atom: Nucleus Electron cloud Chapter 3 – Atomic Structure Atom - Greek for “Atomon” means“Indivisible” - Smallest unit that can exist alone or in combination with other atoms. Structure of an Atom … Things we know Two main areas of the atom: Nucleus - contains protons (+) and neutrons (0) - dense, small Electron cloud - contains electrons (-) - surrounds nucleus, mostly empty space - arranged in shells or energy levels Chapter 3 – Atomic Structure Atom - Greek for “Atomon” means“Indivisible” - Smallest unit that can exist alone or in combination with other atoms. Structure of an Atom … Things we know Two main areas of the atom: Nucleus - contains protons (+) and neutrons (0) - dense, small Electron cloud - contains electrons (-) - surrounds nucleus, mostly empty space - arranged in shells or energy levels Atom itself is neutral: Why? Number of p+ = en0 are neutral - no effect What if you change the number of neutrons? electrons? More on Structure of an Atom … Things we know… Compare size of electron cloud to nucleus Nucleus is extremely tiny compared to the electron cloud. How much smaller????? More on Structure of an Atom … Things we know… Compare size of electron cloud to nucleus Nucleus is extremely tiny compared to the electron cloud. Nucleus “marble” How much smaller????? Nucleus is a marble in the middle of a football stadium. Electron Cloud “football field” More on Structure of an Atom … Things we know… Compare size of proton, neutron, and electron More on Structure of an Atom … Things we know… Compare size of proton, neutron, and electron Nucleus Proton’s mass = 1 amu Neutron’s mass = 1 amu More on Structure of an Atom … Things we know… Compare size of proton, neutron, and electron Electron’s mass = 0 amu Electron Cloud Nucleus Proton’s mass = 1 amu Neutron’s mass = 1 amu More on Structure of an Atom … Things we know… Compare size of proton, neutron, and electron Interesting Stuff … all the mass of the atom is in the nucleus…Wow! What does that mean about the density of the nucleus? Electron’s mass = 0 amu Electron Cloud Nucleus Proton’s mass = 1 amu Neutron’s mass = 1 amu More on Structure of an Atom … Things we know… Compare size of proton, neutron, and electron Interesting Stuff … all the mass of the atom is in the nucleus…Wow! What does that mean about the density of the nucleus? Electron’s mass = 0 amu Nucleus Electron Cloud Proton’s mass = 1 amu Neutron’s mass = 1 amu 1 amu (atomic mass unit) = 1.673 x 10-24 g The atomic mass unit is easier to use to describe something so ridiculously small! 0.0000000000000000 00000001673 g Does an electron having “0” amu means it weighs nothing? Not Exactly … It’s just it is so small it does not matter relatively … More on Structure of an Atom … Things we know… A word about the … amu *amu – atomic mass unit – special unit for the mass of an atom. 1/12 mass of carbon-12 atom. (relative to atom) More on Structure of an Atom … Things we know… A word about the … amu *amu – atomic mass unit – special unit for the mass of an atom. 1/12 mass of carbon-12 atom. (relative to atom) Similar to: 2000 lbs. = 1 ton Easier to say 10 tons than 20,000 lbs. Just like: 1 amu (atomic mass unit) = 1.673 x 10-24 g Easier to say 2 amu than 2.346 x 10-24 g How did we figure out all this stuff about the atom??? Because the atom is so small !!!!! How did we figure out all this stuff about the atom??? Because the atom is so small !!!!! Before I start into the history… …a little bit about Indirect Evidence??? Where to hunt? Measure thickness of paper or a dollar? How did we figure out all this stuff about the atom??? Because the atom is so small !!!!! 400 BC Democritus The idea of the atom stems back to 400 BC by a Greek thinker named Democritus …he called matter “atomon” meaning “indivisible” How did we figure out all this stuff about the atom??? 400 BC Because the atom is so small !!!!! Now, this guy did not have any proof…he just thought about it and told people what he thought … …Good Guess?? Democritus The idea of the atom stems back to 400 BC by this Greek thinker …he called matter “atomon” meaning “indivisible” How did we figure out all this stuff about the atom??? Because the atom is so small !!!!! Click black box for video 1782 Antoine Lavoisier Law of conservation of mass matter cannot be created nor destroyed How did we figure out all this stuff about the atom??? Because the atom is so small !!!!! H2O two H’s one O For this compound to be water… it must have exactly 2 H and 1 O 1799 What is this? H2O2 Joseph Proust Law of definite proportions a chemical compound contains the same elements in exactly the same proportions by mass How did we figure out all this stuff about the atom??? Carbon monoxide CO Because the atom is so small !!!!! C = 12 g O = 16 g C = 12 g O = 32 g Ratio 1 : 1 Carbon dioxide 1803 CO2 Ratio 1 : 2 Same elements but different ratios make different compounds John Dalton Law of multiple proportions If compounds are composed of the same elements, the masses of the elements can be expressed as ratios of small whole #’s. How did we figure out all this stuff about the atom??? Because the atom is so small !!!!! 1803 John Dalton The Atomic Theory 1. All matter is composed of extremely small particles. 2. Atoms of the same element are chemically alike. Atoms of different elements are chemically different. 3. Atoms cannot be divided, created, nor destroyed. 4. Atoms combine in whole # ratios to form compounds. 5. Atoms are combined, separated, or rearranged in chemical reactions. How did we figure out all this stuff about the atom??? Because the atom is so small !!!!! Click black box for video Joseph Thompson 1897 Used a cathod ray tube to prove there were negative charged particles (now known as electrons) in an atom. This opened the way to the idea that an atom was not just a solid sphere not able to be broken down anymore. How did we figure out all this stuff about the atom??? Because the atom is so small !!!!! Robert A. Millikan 1909 Proved that the e- is really small (“0 amu”)…not really…he showed that the e – is 2000 times smaller than the simplest atom Hydrogen (which is only a proton). How did we figure out all this stuff about the atom??? Because the atom is so small !!!!! Earnest Rutherford 1911 In the gold foil experiment, he proved that the electron cloud was huge in volume comparison to the nucleus and the nucleus was extremely dense. How did we figure out all this stuff about the atom??? 1913 Because the atom is so small !!!!! Neils Bohr He proposed a model of the atom that showed that e- circled that nucleus of an atom in only allowed orbits or paths. The Evolving Atomic Model Summary Dalton Model Thomson Model Rutherford Model Bohr Model 1803 – John Dalton believed that an atom was an indestructible particle with no internal frame. 1897 – J.J. Thomson discovers the electron. He believed electrons were embedded in positive charge sphere. 1911 – Ernest Rutherford discovers that there is a dense, positively charged nucleus. Electrons go around the nucleus. 1913 – Niels Bohr enhances Rutherford’s model by having electrons move in a circular orbit at fixed distances from the nucleus. (Billiard Ball Model) (Plum pudding Model) Atomic Number – number of p+ in the nucleus of an atom (always equal to number of e-) Mass Number – number of p+ and n0 in the nucleus of an atom Atomic Weight – the average mass of the isotopes The mass number is the atomic weight rounded off to a whole number!!! Atomic Weight 32.065 Shorthand method: 32 16 S Mass # (rounded) 32 Atomic # (# of p+ or e-)Mass # - Atomic # = n0 Atomic Weight Atomic # Mass # # p+ # e# n0 = = = = = = (Avg. mass of isotopes) = (number of protons or electrons) = (Atomic weight rounded) = (same as Atomic #) = (same as Atomic #) = (Mass # - Atomic #) = Try Sodium (Na): Atomic Weight Atomic # Mass # # p+ # e# n0 = = = = = = (Avg. mass of isotopes) (number of protons) (Atomic weight rounded) (same as Atomic #) (same as Atomic #) (Mass # - Atomic #) = = = = = = 32.066 16 32 16 p+ 16 e 16 n0 (32 – 16) ________ ________ ________ ________ ________ ________ Atomic Weight Atomic # Mass # # p+ # e# n0 = = = = = = (Avg. mass of isotopes) = (number of protons or electrons) = (Atomic weight rounded) = (same as Atomic #) = (same as Atomic #) = (Mass # - Atomic #) = Try Sodium (Na): Atomic Weight Atomic # Mass # # p+ # e# n0 = = = = = = (Avg. mass of isotopes) (number of protons) (Atomic weight rounded) (same as Atomic #) (same as Atomic #) (Mass # - Atomic #) = = = = = = 32.066 16 32 16 p+ 16 e 16 n0 (32 – 16) ________ 22.99 ________ 11 23 ________ 11 ________ 11 ________ 12 ________ PRACTICE THESE………… Au Atomic Weight Atomic # Mass # Ag Pb = (Avg. mass of isotopes) = _______________ = (number of protons) = ______________ = (Atomic weight rounded) = ______________ # p+ = (same as Atomic #) = ______________ # e- = (same as Atomic #) = ______________ # n0 = (Mass # - Atomic #) = ______________ PRACTICE THESE………… Au Atomic Weight = (Avg. mass of isotopes) Atomic # = (number of protons) Ag Pb 196.97 107.87 207.20 = __________________ 79 47 82 = __________________ 197 108 207 Mass # = (Atomic weight rounded) = __________________ # p+ = (same as Atomic #) 79 47 82 = __________________ # e - = (same as Atomic #) 79 47 82 = __________________ # n0 = (Mass # - Atomic #) 118 61 125 = __________________ Isotopes – atoms of the same element with different masses due to a different number of n0 Ex. H has 3 isotopes 1 1H 2 1 H 3 1 H The only thing that changes is the neutrons… …so it is still hydrogen and acts like hydrogen but it is a little heavier with each additional neutron added… If you change the number of neutrons…it is still Carbon but it makes a different isotope. Carbon –12 Carbon - 14 Different number of neutrons 8 IONS: -Atoms that have gained a charge by losing or gaining electrons - An ion with POSITIVE CHARGE has LOST ELECTRONS - An ion with NEGATIVE CHARGE has GAINED ELECTRONS 1 1𝐻 Remember the shorthand we learned? (These are neutral on the periodic table) 1 +1 Now we add in a charge! 𝐻 1 How would you write the shorthand for the Calcium ion with 20 protons, 18 electrons, and 20 neutrons? 40 +2 20𝐶𝑎 Like hydrogen 1 mole = 6.022 x 1023 atoms H NOT --- Even though he is cute! H H O Like water 1 mole = 6.022 x 1023 molecules How do I know how much exactly one mole is? The periodic table… 1 mole = ______g Periodic Table 1 mole of Iron = 55.845 g 1 mole of Zinc = 65.409 g 1 mole of copper = 63.546 g Moles • Mole: the amount of a substance that contains as many particles as there are atoms in exactly 12g of carbon-12. Moles • Avogadro’s Number: the number of particles in exactly one mole of a pure substance ~ 6.02214179 x 1023 (we’ll use 6.02 x 1023) Moles 602,200,000,00 0,000,000,000, 000 If you had 6.022 x 1023 pennies and gave away 1 million a day to every person on earth, it would take you 3000 years to distribute all your money!! 3-30 Molar Mass • Molar Mass: the mass of one mole of a pure substance. ~ the mass of single atoms or molecules is measured in amu’s. The mass of a mole of the same substance is numerically the same, with the units g/mol. Ex. H20 = H x 2 = 1.01 x 2 = 2.02 + O x 1 = 16.00 x 1 = +16.00 18.02g/mol 3-31 Molar Mass 1) What is the molar mass of BaCl2? 2) What is the molar mass of NaI? 3-32 Molar Mass This photograph shows one mole of solid (NaCl 58.44g/mol), liquid (H2O 18.02 g/mol), and gas (N2 28.02 g/mol). 3-33 Mass/Mole Conversions When given the number of moles, you can find the grams by: Moles _g__ = grams 1 mole Ex. 5.0 moles of H2O = X g Mass/Mole Conversions Moles _g_ = grams 1 mol Now try these problems: 3) 8.32 moles of BaCl2 equals how many grams? 4) 20.1 moles of SO2 equals how many grams? 3-35 Mass/Mole Conversions When given the amount in grams, you can calculate the number of moles by: g 1 mol = moles g Ex. 11.2 g NaCl = X moles Mass/Mole Conversions g 1 mol = moles g Now try these problems: 5) 50.56 g of NaCl equals how many moles? 6) 329.8 g of ammonia (NH3) equals how many moles? 3-39 Mass/Mole Conversions Particle/Mole Conversions You can also calculate between moles and number of particles: (1.0 moles = 6.02 x 1023 particles) To enter this number into your calculator, punch in 6.02 EE button (one time) 23. 3-41 Particle/Mole Conversions Ex. 2.59 moles of marble (CaCO3) contains how many molecules? *Particles can be molecules or atoms 7) How many molecules are in 5.0 moles of carbon dioxide? Particle/Mass Conversions Ex. What is the mass of 3.25 x1023 molecules of N2? 8) How many molecules are 57.36 g of NaCl?
