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Chapter 3 Section 3.1: The Atom: From Philosophical Idea to Scientific Theory Atoms: the smallest particle of an element that retains the properties of that element. (Greek: atomos = indivisible) Democritus (Greek teacher in the 4th century BC) First suggested the idea that atoms existed The Atom 1700’s – chemists were able to relate changes to individual atoms Average atom size: Mass = 1 x 10 –23 g Diameter = 1 x 10-8 cm How small is that?100,000,000 copper atoms in a row would = 1 cm in length! Law of Conservation of Mass Definition: mass cannot be created or destroyed only transformed Law of Definite Proportions Definition: a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source Example: ▪ Sodium chloride: NaCl always consists of exactly 39.34% sodium & 60.66%chlorine by mass ▪ Water: H2O always consists of exactly 11.18% hydrogen & 88.82% oxygen by mass Law of Multiple Proportions Definition: if two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers Examples: CO & CO2 : 1:1 ratio & a 1:2 ratio H2O & H2O2: 2:1 ratio & a 2:2 ratio John Dalton English school teacher Proposed an explanation for the 3 laws Established in 1808 Dalton’s Atomic Theory 1. All elements are composed of tiny indivisible particles called atoms. 2. Atoms of the same element are identical. The atoms of any one element are different from those of any other element. 3. Atoms of different elements can combine with one another in simple whole number ratios to form compounds. H2O C12H22O11 NOT H2.5O¾ 4. Chemical reactions occur when atoms are separated, joined or rearranged. Atoms of one element are not changed into atoms of another by chemical means! 5. Atoms can not be subdivided. Section 3.2 – The Structure of the Atom Most of Dalton’s Atomic Theory is accepted One major revision includes that idea that atoms are indivisible…. There are 3 parts to an atom…. 1. electrons 2. protons 3. neutrons Discovery of the Electron Negatively charged subatomic particles J.J. Thomson discovered in 1897 Passed a electric current through gases at low pressures called a “Cathode Ray Tube” Noticed the surface of the tube directly opposite the cathode glowed. Why? Opposites attract and the electrons were attracted to the positive ends and lights up! Cathode Ray Tube Cathode Ray Tube Cathode rays are identical regardless of the element Therefore all elements must have electrons! Other important findings: Atoms are electrically neutral, so they must contain a positive charge to cancel it out Since electrons are so small, atoms must contain other particles that account for their mass Robert Millikan (1868-1953) Found quantity of charge in 1 electron (e-) Also determined the ratio of the charge to the mass of 1 e Calculated the mass of 1 eElectrons weigh 9.109 x10-31 kg J.J. Thomson – plum-pudding model e- are spread evenly though out the positive charge of the rest of the atom Ms. Agostine’s “mint chocolate chip ice cream model” Ernest Rutherford (1911) nucleus of the atom is positively charged Gold Foil Experiment Most particles go straight through Positively charged particles deflect off of the positively charged nucleus(~1/8,000) Gold Foil Experiment “…it was as if you fired a 15-inch [artillery] shell at a piece of tissue paper and it came back and hit you.” Nucleus was very small If a nucleus were a marble the atom would be a football field Protons (p+) Positively charged particles Mass = 1.673 x 10-27 kg 1,836 times heavier then an electron Neutrons (no) Subatomic particles with no charge Discovered by Sir James Chadwick Mass is nearly the same as a proton Mass = 1.675x10-27 kg Particle Symbol Relative Charge Electron e- 1- Relative Mass (amu) 1/1836 Actual Mass (kg) Proton p+ 1+ 1 1.67x10-27 neutron no 0 1 1.68x10-27 9.11x10-31 Atomic Number : the number of protons in the nucleus of an atom of an element Atoms are electrically neutral Tells how many electrons there are also! Periodic Table #1 – Hydrogen: has 1 p+ and 1 e#6 – Carbon: has 6 p+ and 6 e- Mass Number – total number of protons and neutrons in a nucleus # of neutrons = mass # - atomic # = (# p+ + # no) - (# p+) Ex) Beryllium – 9 Hyphen notation: The number “9” is the mass number # of p+? # of no? # of e-? Definition – atoms that have the same number of protons but different numbers of neutrons Different types of the same element Ex) Carbon – has 3 isotopes Carbon – 12 Carbon – 13 Carbon – 14 Differ by # of no All have the same # of p+ If not, it would be a different element All have 6 protons Carbon – 12 Has 6 neutrons Carbon – 13 Has 7 neutrons Carbon – 14 Has 8 neutrons Hydrogen-1: 1 p+ and 0 no Relative abundance = 99.985 % Commonly called normal “hydrogen” Hydrogen-2: 1 p+ and 1 no Relative abundance = 0.015% Commonly called heavy hydrogen or “deuterium” Hydrogen-3: 1 p+ and 2 no Relative abundance = ~0.00% Commonly called “tritium” Definition – weighted average mass of the atoms in a naturally occurring sample of the element Carbon-12 = 98.89 % abundant Carbon-13 = 1.11% abundant Carbon-14 = ~0.0000001% abundant Formula: Atomic = relative • mass # + relative • mass # mass abund. # abund. + Repeats for as many isotopes as exist for that element…. Units: atomic mass unit (amu): defined as exactly 1/12 the mass of a carbon-12 atom 1 amu = approximately the mass of 1 proton amu’s are used so you don’t have to use scientific notation when talking about such small masses Sample Problem: Chlorine has 2 isotopes: chlorine-35 which is 75.77% abundant and chlorine-37 which is 24.33% abundant. What is the atomic mass of chlorine? 35 Cl = 75.77% abundant = 0.7577 rel. abund. 37 Cl = 24.33% abundant = 0.2433 rel. abund. Atomic mass = = (35 amu x 0.7577) + (37 amu x 0.2433) = (26.5195 amu) + (9.0021 amu) = 35.5 amu Compare to value on Periodic Table = 35.45 amu which rounds to 35.5 amu We must have a way to relate masses in grams to numbers of atoms… How many definitions did you come up with? Any of various small insectivorous mammals, living chiefly underground. 2. A spy who becomes part of and works from within the ranks of an enemy governmental staff or intelligence agency. 1. 3. Machinery. A large, powerful machine for boring through earth or rock, used in the construction of tunnels. 4. A small, congenital spot or blemish on the human skin, usually of a dark color, slightly elevated, and sometimes hairy. 5. A massive structure, esp. of stone, set up in the water, as for a breakwater or a pier. 6. An anchorage or harbor protected by such a structure. 7. A fleshy mass in the uterus formed by a hemorrhagic dead ovum. (ew) 8. A spicy sauce flavored with chocolate, usually served with turkey or chicken. 9. The amount of a substance that contains as many atoms, molecules, ions, or other elementary units as the number of atoms in 12.01 g C. The number is 6.02 × 1023, or Avogadro's number. Named in honor of Amedeo Avogadro di Quaregna (1776-1856) Proposed: Equal volumes of different gases at the same temperature and pressure, contain the same number of molecules. How do you order donuts? How do you order cans of soda? How do you order computer paper? How do you order jelly beans? How do you order lunchmeat? You use a counting/measuring amount! 1 1 1 1 1 dozen donuts = 12 donuts case of soda = 24 cans ream of paper = 500 sheets pound of jelly beans = ~350 j.b. pound of turkey = ~25 slices How big is that number really?!?! 602,000,000,000,000,000,000,000 How long of a paper clip chain? How big of a marshmallow mountain? How big of a marble mountain? How tall would a stack of pennies be? How big is that number really?!?! 602,000,000,000,000,000,000,000 1 mole of paperclips: goes around earth 4 trillion times 1 mole of large marshmallows: cover the continental USA 650 miles deep 1 mole of marbles: 116 times the size of Mt. Everest 1 mole of pennies stacked up: distance to the moon 1.55x1012 times = 1,550,000,000,000 times! How much is a mole of water molecules? Is equal to 18 mL …that’s how small molecules really are! Mole of iron = 55.85 g Mole of sulfur = 32.07 g It’s not individual grains of iron or sulfur! Where are these numbers coming from? …Periodic table!!! Definition: the mass of one mole of a substance (Units: g/mol) AKA the atomic mass on the periodic table Round all elements masses to two decimal places Exception: Hydrogen gets 3 decimal places 12.0 grams of Carbon and 1.0 gram of Hydrogen contain the same number of atoms 6.022 x 1023 atoms The gram atomic mass of any two elements must contain the same number of atoms Carbon = 12.0107 g/mol Rounds to 12.01 g/mol Oxygen = 15.9994 g/mol Rounds to 16.00 g/mol Hydrogen = 1.00794 g/mol Rounds to 1.008 g/mol What if you have a compound? 1 mole NaCl = 58.44 g/mol How did you get that mass? NaCl 1 Na = 22.99 g/mol + 1 Cl = 35.45 g/mol 58.44 g/mol What is the molar mass of sugar? C12H22O11? C12H22O11 12-C x 12.01g/mol = 144.12 g/mol 22-H x 1.008 g/mol = 22.176 g/mol + 11-O x 16.00 g/mol = 176.0 g/mol 342.30 g/mol What is the molar mass of aluminum sulfate? Al2(SO4)3 Count the atoms! Al = ____, S=____, O=_____ What is the molar mass of aluminum sulfate? Al2(SO4)3 Count atoms - (distribute the 3) Al = 2, S=3, O=12 Al2(SO4)3 2-Al x 26.98 g/mol = 53.96 g/mol 3-S x 32.07 g/mol = 96.21 g/mol + 12-O x 16.00 g/mol = 192.0 g/mol 342.17 g/mol 1. Gram Atomic Mass (gam) 2. Gram Molecular Mass (gmm) 3. Gram Formula Mass (gfm) GAM: molar mass of an atom or element Ex) Fe, Cu, P, S… GMM: molar mass of a molecule (nonmetal compound) Ex) H2O, Cl2, O2, CO2, P2O5 GFM: molar mass of a formula unit (ionic compounds) Metal-nonmetal compounds Ex) NaCl, FeBr3, Zn3(PO4)2 If one mole of water is 18.02 g, how much would two moles weigh? 36.04 g How much would 3 moles weigh? 54.06 g If one mole of water is 18.02 g, how many moles are in 90.1 g? 5 moles Three types of Mole Conversions Mole Mole – mass (g) – representative particles (molecules, atoms, formula units) Mole – volume (L) What is the mass of 4 moles of NaCl? Given: Unknown: Conversion Factor: Solve: Given: 4 moles NaCl Unknown: g NaCl Conversion Factor: molar mass of NaCl 1 mole NaCl = 58.44 g NaCl Solve: 4 mol NaCl x 58.44 g NaCl = 233.76 g NaCl 1 mol NaCl How many moles is 321.42 g NaCl? Given: Unknown: Conversion Factor: Solve: Given: 321.42 g NaCl Unknown: mole NaCl Conversion Factor: molar mass of NaCl 1 mole NaCl = 58.44 g NaCl Solve: 321.42 g NaCl x 1 mol NaCl = 5.5 mol NaCl 58.44 g NaCl How many moles is 2.107x1024 mo of O2? Given: Unknown: Conversion Factor: Solve: Given: 2.107x1024 mo O2 Unknown: mol O2 ? Conversion Factor: Avogadro’s # 1 mole O2 = 6.02x1023 mo O2 Solve: 2.107x1024 mo O2 x 1 mol NaCl = 3.5 mol O2 6.02x1023 mo O2 How many atoms are in 12.5 moles of Copper? Given: Unknown: Conversion Factor: ? Solve: Given: 12.5 mol Cu Unknown: at Cu? Conversion Factor: Avogadro’s # 1 mole Cu = 6.02x1023 at Cu Solve: 12.5 mol Cu x 6.02x1023 at Cu = 7.53x1024 at Cu 1 mol Cu If one mole of Helium weighs 4.00 g/mol, how much does 2 moles weigh? Can you weigh out something less dense then air? You CANNOT weigh a gas less dense then air! Gravity does not pull it down on the scale! The volume of mole of a gas is much more predictable than that of a liquid or solid That is, under the same physical conditions (STP) Standard temperature and pressure ▪ Standard Temperature is 00C ▪ Standard Pressure is 1 atm At STP, 1 mole of any gas will occupy a volume of 22.4 L 22.4 L is known as the molar volume of a gas What does it mean? It means that 22.4 L of any gas at STP contains 6.02 X 1023 representative particles of that gas. Standard Temperature and Pressure (STP): specific conditions that can be reached in the lab Standard Pressure: 1 atmosphere (atm) Standard Temperature: 0oC or 273 K Temperature = a measurement of the average kinetic energy of the particles of an object Scales Fahrenheit (oF) Celsius (oC) Kelvin (K) Boiling Point Room Temp Freezing Point Absolute Zero – coldest possible temperature where all movement stops, theoretical value 0 Kelvin = -273.15 oC = -459 oF Equations: K = oC +273 oC = K – 273 Example: What is 98 K = _-175 oC? What is 159 oC = _432 K? How many moles is 145.6 L of O2 gas at STP? Given: Unknown: Conversion Factor: Solve: Given: 145.6 L O2 Unknown: mol O2 ? Conversion Factor: molar volume 1 mole O2 = 22.4 L O2 Solve: 145.6 L O2 x 1 mol O2 = 6.500 mol O2 22.4 L O2 How many liters is 11 moles of O2 gas at STP? Given: Unknown: Conversion Factor: Solve: Given: 11 mol O2 Unknown: L O2 Conversion Factor: molar volume 1 mole O2 = 22.4 L O2 Solve: 11 mol O2 x 22.4 L O2 1 mol O2 = 246.4 L O2 How many liters of gas are 3.612x1024 atoms of Neon gas at STP? Given: Unknown: Conversion Factor: Solve: Given: 3.612x1024 atoms Neon Unknown: L Ne Conversion Factor: needs TWO! Avogadro’s number 1 mole Ne = 6.02x1023 at Ne molar volume 1 mole O2 = 22.4 L O2 THERE IS NO DIRECT ROAD FROM ATOMS L Solve: 3.612x1024 at Ne x __1 mol Ne_ x 22.4 L Ne = 6.02x1023 at Ne 1 mol Ne In your calculator it looks like this: 3.612e24 x 1 x 22.4 ÷ 6.02e23 ÷ 1 = 134.4 L Ne