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001 Atomic Structure and Isotopes

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001 Atomic Structure and Isotopes Powered By Docstoc
					Chemistry
Main Topic: Intro. to Modern Concept of Atomic Structure (Ch. 4.6-7)                        Reading: Ch. 4.3 through 4.7
Focus: Students will be able to: 9PS1,2,6 11PS#1
    describe the structure of the modern nuclear atom and the characteristics of subatomic particles.
    be able to use atomic notation to calculate the # of p, n, e in an atom.
                                                                 -

    be able to define “isotope” and calculate the atomic mass of a naturally-occurring element.
Materials:
    Pennies             Pennium activity handout            Atomic Structure & Isotopes WS
Procedure
1. Atomic Structure
      a. Describe an atom: Invisible w/ any light microscope (smaller than a wavelength of light), but not a solid
          sphere: contains subatomic particles.
      b. Review models:
              i. Early Greeks - conceived of matter as being made up of tiny, indestructible, indivisible particles of
                   matter: atomos. This was the guiding concept from 2000 B.C., even into the 1800‟s.
                ii.   John Dalton - early 1800‟s brilliant young scientist studied compounds & their chemical formulas.
                      Discovered that any given compound always has the exact same chemical formula (Law of Definite
                      Proportions). Next, he studied atoms. Building on Greek concepts, he came up with 4 attributes for
                      atoms:
                         o Atoms are tiny, indestructible spheres.
                         o Atoms of any one element are identical. Atoms of different elements can be distinguished
                             because they have different masses.
                         o Compounds are made by joining atoms in whole-number ratios. Like a recipe: 1 of this, 2 of
                             that, etc.
                         o Since atoms are indestructible, matter cannot be created or destroyed in any normal chemical
                             reaction. Law of Conservation of Mass. In a chemical reaction, atoms simply re-arrange
                             into new structures or compounds.
                iii. J.J. Thompson - 1890‟s, discovered that atoms could be forced to emit a tiny, negatively-charged
                     particle, which he called the electron. Thompson envisioned an atom as being like raisin bread:
                     electrons (the raisins) evenly distributed throughout a globe of positive charge.
                iv. Ernst Rutherford was experimenting with radioactivity in 1911. He discovered that if you “shine”
                    radioactive particles on a thin film of Au foil, most of the particles simply go through, but a few get
                    reflected back towards you. From this, he concluded that an atom must have a dense, positive
                    nuclear core, surrounded by mostly empty space (with the electrons in the otherwise empty region).
                v.    Modern model - “charged cloud model”
                                                           -8                         -
                                                        10 cm (1 angstrom), e charge cloud, 99.99999% of the volume
                                                           -13                                                    +
                                                        10       cm, contains 99.99999% of the mass, p & neutrons
                                             If a baseball were increased to the size of the earth, the atoms in it would be the size of
                                             pingpong balls, and you‟d still need a microscope to see the nuclei !!!

                                                                                    12
                vi. Subatomic particles - explain amu = atomic mass unit; C is the standard for mass.
                         Particle        Location       Charge          Mass
                                                                                +
                         Electron      Outer cloud         -1       1/1836 of p
                          Proton          Nucleus          +1          1 amu
                         Neutron          Nucleus           0         1 amu +
                                  -
                vii. Electrons (e )
                       Accounts for the bulk of the atom
                                                      -
                       Number and arrangement of e determines the chemical properties of an element.
                                                              -
                       Neutral free atoms have the same # of e as protons.
                                                                                            -
                       An atom can lose or gain 1 or more electrons to become ions. Since e are negative, an atom that
                                loses an electron becomes a +1 ion. An atom that gains an electron becomes a -1 ion.
                                                                                        +2
                       Ca can lose 2 electrons. What kind of ion will it become? Ca
                                                                                     -3
                       P can gain 3 electrons. What kind of ion can it become? P
                viii. Protons (p), atomic number (Z)
                        All atoms of the same element have the same number of protons - # of protons is what makes an
                                 element that element.
                        # of protons = atomic number. Can find Z for any element, by looking on periodic table.
                        How many protons are there in Cr? 24
                        What is the atomic number of Ca? 20
                        If a neutral atom of Na has 11 protons, how many electrons does it have? 11
                        What element has an atomic number of 15, what element is it? P

                ix. Neutrons (n) and mass number (A).
                     Not all atoms of the same element have the same number of neutrons. Atoms of the same element
                              with different numbers of neutrons are isotopes.
                     Sum of protons + neutrons in an atom‟s nucleus is its mass number (A).

                x.   Atomic Notation
                      A   charge
                       ZX                  12
                      The notation for C is 6C. How many p, n, e? 6 of each.
                      35     -1                                 -
                        17Cl    How many p,n,e? 17 p, 18 n, 18 e .
                      39   +                 -
                        19K 19 p, 20 n, 18 e .
                      Do problem 42 pg. 119 now as concept check.

2. Isotopes - Again, atoms of the same element (same # p) but with different #‟s of n. This makes their masses slightly
   different.
                             1              2               3
        a. Best known are 1H (protium), 1H (deuterium), 1H (tritium).
                                               35        37
            What’s the difference between 17Cl and 17Cl ?
            Which of the following pairs are isotopes?
            20       21                  79        79 -1      207         207
              Ne and Ne                    Br and Br             Pb and Bi
        b. The Atomic Mass of an element is slightly different than its mass number. The atomic mass is the average
           mass of all the isotopes of an element in a naturally-occurring sample. In nature, the different isotopes don‟t
           all occur with equal abundances.
                                                                 12                                 13      14
               i. For example: in C, 98% of all the atoms are C; the other 2% are made up of C and C (the type of
                   C that‟s used in radiocarbon dating of archeological artifacts.) The „average‟ atom, therefore, has an
                   atomic mass of just a little over 12 (12.011). The units for atomic mass are a.m.u. For Br, about 51%
                                     79             81
                   of the atoms are Br; 49% are Br. The average atomic mass is just under 80 (79.9).
                                                   12
        c.   The standard for atomic mass is the    C atom. The world chemical community has decided to make the mass
             of this atom = exactly 12 a.m.u.
        d. Determining Atomic Masses from Weighted Averages
              How would you determine your test average if you were given the following list?
                       Test Score Weight (% of total grade)
                        1      95        10%
                        2      80        20% (95 x .1) + (80 x .2) + (75 x .3) + (90 x .4)
                        3      75        30% = 84 (average score)
                        4      90        40%
              Atomic masses are done in just the same way. Mass number is the „test score‟ and relative abundance
                      (% of the total atoms that are that isotope) is the „weight‟.

                Try the following: Calculate the atomic mass of Cl.
                                 35                        37
                77.36% of Cl is Cl                22.64% is Cl           (35 x .7736) + (37 x .2264) = 35.45


3. HW - Atomic Structure & Isotopes WS
4. EVAL - HW, test
Name ________________________________________________                                                                    / 10 pts
                                                            Atomic Structure

1) The nucleus of an atom contains positively charged _____________________________.
2) The nucleus of an atom may also contained uncharged __________________________.
3) How do the masses of the proton, neutron, & electron compare to each other?




4) An „average‟ atomic nucleus has a radius of ________________________ meters.
5) The ______________ of an atom determines its chemical behavior, but the _______________ determines its mass.
6) The ____________________ number of an atom indicates the number of protons present in the atom.
7) The ____________________ number of an atom indicates the total number of protons + neutrons present.
8) For a neutral atom, the number of protons & _____________________ must be the same.
                             A      charge
9) Write the atomic notation ( ZX            ) for each of the particles described below.
        a) 8 protons, 9 neutrons, 10 electrons.                                   b) neutral element # 92 with 146 neutrons


        c) the isotope of iron with 30 neutrons and 23 electrons                  d) atomic # = 19, mass # = 39, 18 electrons




Name ________________________________________________                                                                    / 10 pts
                                                            Atomic Structure

1) The nucleus of an atom contains positively charged _____________________________.
2) The nucleus of an atom may also contained uncharged __________________________.
3) How do the masses of the proton, neutron, & electron compare to each other?




4) An „average‟ atomic nucleus has a radius of ________________________ meters.
5) The ______________ of an atom determines its chemical behavior, but the _______________ determines its mass.
6) The ____________________ number of an atom indicates the number of protons present in the atom.
7) The ____________________ number of an atom indicates the total number of protons + neutrons present.
8) For a neutral atom, the number of protons & _____________________ must be the same.
                             A      charge
9) Write the atomic notation ( ZX            ) for each of the particles described below.
        a) 8 protons, 9 neutrons, 10 electrons.                                   b) neutral element # 92 with 146 neutrons


        c) the isotope of iron with 30 neutrons and 23 electrons                  d) atomic # = 19, mass # = 39, 18 electrons
10) Which pair(s) of particles have the same number of neutrons?

        a) 12C 14C                b) 12C 13N              c) 108Ag 108Sn                   d) 2H 1H

11) Write in the atomic notation, the number of protons, neutrons, and electrons that each of the following particles has
        from the clues given.
        atomic not.     protons          neutrons         electrons
        27
          13Al          ______           _______          _______
        _________       __51__           __73___          __47___
        40
          18Ar          ______           _______          _______
        80     -1
          35Br          ______           _______          _______
        _________       __11__           __12___          __10___
        40   +1
          19K           ______           _______          _______
        _________       __15__           __16___          __18___
        _________       __15___          __16___          __10___




10) Which pair(s) of particles have the same number of neutrons?

        a) 12C 14C                b) 12C 13N              c) 108Ag 108Sn                   d) 2H 1H

11) Write in the atomic notation, the number of protons, neutrons, and electrons that each of the following particles has
        from the clues given.
        atomic not.     protons          neutrons         electrons
        27
          13Al          ______           _______          _______
        _________       __51__           __73___          __47___
        40
          18Ar          ______           _______          _______
        80     -1
          35Br          ______           _______          _______
        _________       __11__           __12___          __10___
        40   +1
          19K           ______           _______          _______
        _________       __15__           __16___          __18___
        _________       __15___          __16___          __10___
Name ________________________________________________                                                          / 5 pts
                                                            Isotopes

1)   T / F   Atoms that have the same number of neutrons but different numbers of protons are isotopes.

2) Which of the following pairs are isotopes?
          32 -2 16 -2                24    25                     20 -   20             137    137        +2
       a) S         O             b) Mg      Mg              c)    F          Ne   d)     Ba         Ba
                                               24      25          26
3) Magnesium exists in 3 different isotopes:      Mg        Mg         Mg

        a) How many protons are in 1 atom of each of these three isotopes?

        b) How many neutrons are in 1 atom of each of these three isotopes?

        c) Calculate the atomic mass of Mg, given the % abundances of the 3 isotopes.
        24                      25                      26
          Mg    78.60%            Mg    10.11%            Mg  11.29%




Name ________________________________________________                                                          / 5 pts
                                                            Isotopes

1)   T / F   Atoms that have the same number of neutrons but different numbers of protons are isotopes.

2) Which of the following pairs are isotopes?
          32 -2 16 -2                24    25                     20 -   20             137    137        +2
       a) S         O             b) Mg      Mg              c)    F          Ne   d)     Ba         Ba
                                               24      25          26
3) Magnesium exists in 3 different isotopes:      Mg        Mg         Mg

        a) How many protons are in 1 atom of each of these three isotopes?

        b) How many neutrons are in 1 atom of each of these three isotopes?

        c) Calculate the atomic mass of Mg, given the % abundances of the 3 isotopes.
        24                      25                      26
          Mg    78.60%            Mg    10.11%            Mg  11.29%
Just for fun (and 5 pts. extra credit!)
                                                              Radioactive Arithmetic
Fill in the number that answers each statement, and do the arithmetic indicated. Your final answer will be the value for the half-life of carbon-14 (14C).
Skimming through Chapter 19 in your book might be helpful.

     1.   The mass number of the radioactive uranium isotope most commonly used
              as a nuclear fuel.                                                                                    ________
     2.   The number of grams of Rhodium-106 that remain after 60 seconds, if you start with
              a 100 gram sample, and Rhodium-106‟s half life is 30 seconds.                             X          =________

     3.   The atomic number of radioactive   234
                                                Th                                                      -          =________

     4.   The number of protons in the nucleus of a uranium atom                                        -          =________

     5.   The mass number of the simplest of all isotopes of hydrogen.                                  +          =________

     6.   The difference between the atomic numbers of Au and Pb.                                       /          =________

     7.   The atomic number of an atom having 3 protons                                                 X          =________

     8.   The mass number of a common non-flammable gas used in balloons.                               -          =________

     9.   The non-radioactive isotope of Ba that you get if you round off the atomic mass of            -          =________
              Ba to the nearest whole number.

     10. The mass number of a fluorine atom having 9 protons & 10 neutrons                              +          =________


The half-life of a Carbon-14 nucleus (in years):                                                                   =_______




Just for fun (and 5 pts. extra credit!)
                                                              Radioactive Arithmetic
Fill in the number that answers each statement, and do the arithmetic indicated. Your final answer will be the value for the half-life of carbon-14 (14C).
Skimming through Chapter 19 in your book might be helpful.

     1.   The mass number of the radioactive uranium isotope most commonly used
              as a nuclear fuel.                                                                                    ________
     2.   The number of grams of Rhodium-106 that remain after 60 seconds, if you start with
              a 100 gram sample, and Rhodium-106‟s half life is 30 seconds.                             X          =________

     3.   The atomic number of radioactive   234
                                                Th                                                      -          =________

     4.   The number of protons in the nucleus of a uranium atom                                        -          =________

     5.   The mass number of the simplest of all isotopes of hydrogen.                                  +          =________

     6.   The difference between the atomic numbers of Au and Pb.                                       /          =________

     7.   The atomic number of an atom having 3 protons                                                 X          =________

     8.   The mass number of a common non-flammable gas used in balloons.                               -          =________

     9.   The non-radioactive isotope of Ba that you get if you round off the atomic mass of            -          =________
              Ba to the nearest whole number.

     10. The mass number of a fluorine atom having 9 protons & 10 neutrons                              +          =________


The half-life of a Carbon-14 nucleus (in years):                                                                   =_______
Name                                                                                     / 20 pts (as a lab report grade!)

                                   5 Major Contributors to the Concept of the Atom

For each of the 5 men below, describe his contribution to our understanding of the atom. Be specific about their ideas or
discoveries. (For example, don’t say “he came up with the atomic theory”. That‟s vague. Instead, explain what the ideas
behind the atomic theory are.) Your responses must be concise and to-the-point. Therefore, use no more than 2
complete sentences for each person.

       Democritus (an ancient Greek)




       John Dalton




       J.J.Thomson




Name                                                                                     / 20 pts (as a lab report grade!)

                                   5 Major Contributors to the Concept of the Atom

For each of the 5 men below, describe his contribution to our understanding of the atom. Be specific about their ideas or
discoveries. (For example, don’t say “he came up with the atomic theory”. That‟s vague. Instead, explain what the ideas
behind the atomic theory are.) Your responses must be concise and to-the-point. Therefore, use no more than 2
complete sentences for each person.

       Democritus (an ancient Greek)




       John Dalton




       J.J.Thomson
   Ernst Rutherford




   Neils Bohr




   Ernst Rutherford




   Neils Bohr

				
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