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Early Atomic Theory and Structure Chapter 5.1 Early Thoughts o Roots of atomic theory are as old as 440 B.C. with Democritus’ idea of the atom o It took 2 000 years for us to expand on this idea. The new theory was to be done by an English schoolmaster John Dalton in the early 1800s. Dalton’s Atomic Theory o o o o His theory included 6 postulates 1. Elements are made up of atoms 2. Atoms of the same element are alike 3. Atoms of different elements are different by virtue of their size and mass o 4. Chemical compounds are formed by the union of two or more atoms of different elements o 5. Atoms combine to form compounds in whole number ratios (1:2 or 2:2, etc] o 6. Atoms of two elements may combine in different ratios to form more than one compound 5.4 - 5.8 Subatomic Particles o Through the years of the late 1800s and into the early 1900s it was determined that there are three subatomic particles o Electrons (discovered first) o Protons (reasoned to exist if elements are neutral) o Neutrons (discovered last) Electrons o Occupies the area outside the nucleus o Negative charge, o Relative to the other subatomic particles it has negligible (so small that it can be ignored) mass. Protons o Occupies area in the nucleus, o Positive charge o Mass roughly equal to neutrons Neutron o Occupies Nucleus o No charge o Roughly the same mass as the proton Answers of the Day Particle Charge Location Relative (in/out Mass side (0 or 1) nucleus) Inside 1 nucleus Proton positive Electron negative outside nucleus 0 Neutron neutral 1 inside nucleus Atomic Number oAtomic Number = the number of protons; unique to each element and the order of the periodic table is arranged Mass number oMass Number = protons + neutrons (whole number) oCannot be found on the periodic table! Charge = # protons - # electrons CHARGE Self Check o What is the charge of a substance with 14 protons, 15 neutrons, and 14 electrons? o Now let’s begin the grid . Check yourself o The nucleus is made up of what two types of subatomic particles? Same element different mass ISOTOPES Isotopes oIsotopes have same number of protons (so they are the same element) but different number of neutrons oSome isotopes are radioactive ISOTOPIC NOTATION isotopes are atoms with the same number of protons but different number of neutrons A Z X A = mass number (the total number of protons + neutrons) Z = atomic number (the total number of protons) X = element symbol READING ISOTOPIC NOTATION 46 21 Sc 46 = mass number (the total number of protons (21) + neutrons (25) 21 = atomic number (the total number of protons (21) Sc = element symbol In a neutral atom, the number of electrons (21) is equal to the number of protons. PRACTICE PROBLEMS 15N 7 # protons = ____ ___ 35P 15 # p = ____ 62Cu2+ 29 # p = ____ 76Se3- 34 # p = ____ 8 # neutrons= ____ #electrons = 7 # n=20 ____ 15 #e- = ___ 33 # n= ____ 27 #e- = ___ 42 # n= ____ #e- =37 ___ Formulas you should know o Atomic number = # of protons o In an atom (uncharged): o # of protons = # of electrons o Mass # = # protons + # neutrons or o # neutrons = mass # - # protons o Charge = # protons - # electrons (for ions) o Remember the atomic # and # of protons give the element its identity and does not change Test your Knowledge Name Symbol Atomic # # of protons neon # of neutrons Mass # 11 Pb 207 74 110 88 226 8 carbon F 19 79 118 # of electrons Test your Knowledge Name Symbol Atomic # # of protons # of neutrons Mass # # of electron s neon Ne 10 10 11 21 10 lead Pb 82 82 125 207 82 tungsten W 74 74 110 184 74 radium Ra 88 88 138 226 88 carbon C 6 6 8 14 6 fluorine F 9 9 10 19 9 gold Au 79 79 118 197 79 Elements composed of atoms Elements or atoms in an unbonded state have the same number of electrons as protons (They are neutral) Ions Ions have an unequal number of electrons and protons. An atom loses or gains electrons to take on a charge (protons/neutrons are not transferred) Charge = #protons - # electrons Ionic Notation 3X This means that this element has a -3 charge. Self Checker o If a substance has a charge of +2, this means that the number of protons is (circle one: LESS than or GREATER than) the number of electrons? Writing ISOTOPIC NOTATION 1. Write the symbol for the atom with an atomic number of 21 and a mass number of 48. 48 Sc 2. Give the complete chemical notation for the nuclide with 23 protons, 26 neutrons and 20 electrons. 49V3+ 3. Write the isotopic notation for 110Pd a. Z = 46 A = 110 b. An atom containing 24 protons, 28 neutrons, and 21 electrons 52Cr3+ c. Titanium-50 50Ti PRACTICE PROBLEMS 1. 196 Pt4+ 118 78 # n = _____ # p = _____ 196 mass number = ________ 195.1 amu atomic mass = ________ 78 #e- = _____ 78 atomic number = _______ platinum name of element = _______ 2. Indicate the appropriate mass number of an element with 30 protons, 30 neutrons, and 28 electrons. 196 Atomic Mass oAtomic Mass = number on the periodic table reflecting the mass all isotopes known and their relative percentages (on periodic table below element’s symbol--usually not a whole number) Atomic Mass o The atomic mass of an element represents the average mass of all the isotopes found in nature. No element exists with only one possible isotope. Hydrogen has the smallest number of isotopes: 1H protium, 2H deuterium, 3H tritium. Its atomic mass is 1.0079 amu (atomic mass units). The atomic mass is calculated by adding the % of 1H mass found in nature to the % of 2H mass found in nature plus the % of 3H mass. o % 1H + % 2H + % 3H = average mass (atomic mass) o Generally the formula used is: % X + % Y + % Z… = atomic mass. An instrument called the mass spectrometer is generally used to determine the percentages and individual masses of each isotope. Atomic Mass o Silver is found to have two stable isotopes, one has an atomic mass of 106.904 amu and the other weighs 108.905 amu. The first isotope represents 51.82 % of the mass of the element and the second represents 48.18 %. What is the atomic mass of the element silver? The equation to use is %X (mass X) + % Y (mass Y) = average And remember to turn your percents into fractions before multiplying. (0.5182) 106.904 amu + (0.4818) 108.905 amu =? 55.398 amu + 52.470 amu =? 107.868 amu !! Now look at the periodic table to verify the answer. PRACTICE PROBLEMS # 8 1. A sample of neon contains three isotopes, neon-20 (with an isotopic mass of 19.9924 amu), neon-21 (20.9939 amu) and neon-22 (21.9914 amu). The natural abundances of these isotopes are 90.92%, 0.257 %, and 8.82 %. Calculate the atomic weight of neon. 20.17 amu 2. There are only two naturally occuring isotopes of copper, 63Cu and 65Cu. Copper has an atomic mass of 63.55 amu. What is the natural abundance of each isotope? 65Cu = 30% & 63Cu = 70% 3. There are only two naturally occuring isotopes of gallium, 69Ga and 71Ga. What is the natural abundance of each isotope? 69Ga = 60% and 71Ga = 40% GROUP STUDY PROBLEM #8 _______1. The element with atomic number 53 contains a) 53 neutrons b) 53 protons C) 26 neutrons & 27 protons d) 26 protons & 27 neutrons _______2. The mass of one atom of an isotope is 9.746 x 10-23 g. One atomic mass unit has the mass of 1.6606 x 10-24 g. The atomic mass of this isotope is a) 5.870 amu b) 16.18 amu c) 58.69 amu d) 1.627 amu 108 _______3. The number of neutrons in an atom of a) 47 b) 108 c) 155 47 Ag is d) 61 27 Al3+ _______4. The number of electrons in an ion of 13 is a) 13 b) 10 c) 27 d) 14 _______5. What is the relative atomic mass of boron if two stable isotopes of boron have the following mass and abundance: 10.0129 amu (19.91%) & 11.0129 (80.09%) a) 10.81 amu b) 10.21 amu c) 10.62 amu d) 10.51 amu Table Information Hydrogen H Atomic Number 1 Atomic Weight 1.00794 Oxidation States +1, -1 Electronegativity, Pauling 2.2 State at RT Gas, Non-metal Melting Point, K 14.01 Boiling Point, K 20.28 Symbol The Periodic Table o Horizontal rows are called periods o Vertical columns are called groups o We will use 1- 18 as group designations. o Group 1 is Alkali Metals o Group 2 is the Alkaline Earth Metals o Group 18 Inert or Noble Gases o Group 17 Halogens Larger Groups o Groups 3 –12 are the heavy metals or transition elements o Two periods at the bottom are called the rare earth elements or the inner transition elements. Comparing Regions of the Periodic Table Property Metals Metalloids Nonmetals Physical State at room temperature Mostly Solids (liquid Hg) ALL Solids Some Gases Some Solids One Liquid (Br) Melting Point Very High Intermediate Very Low Conductivity Very Good Conductors Semi-conductors Poor conductors (Good insulators) Magnetism Good Intermediate Poor