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3: Atoms and Elements

  • Page ID
    279973
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    The Nuclear Atom

    Exercise \(\PageIndex{1.a}\)

    How are electrons and protons similar? How are they different?

    Answer

    Both are subatomic particles. Protons are positively charged, and reside in an atom’s nucleus. Whereas, electrons are negatively charged and reside outside an atom’s nucleus.

    Exercise \(\PageIndex{1.b}\)

    How are protons and neutrons similar? How are they different?

    Answer

    Both are subatomic particles that reside in an atom’s nucleus. Both have approximately the same mass. Protons are positively charged, whereas neutrons are uncharged.

     

    The Elements

    Exercise \(\PageIndex{2.a}\)

    Name the following element

    Ra, Rn, Mg & Mn

    Answer

    radium, radon, Magnesium & Manganese

    Exercise \(\PageIndex{2.b}\)

    Name the following element

    Pb, Pa, Pu, Pt & Po

    Answer

    Lead, Protactinium, Plutonium, Platinum & Lead

     

    Exercise \(\PageIndex{2.c}\)

    Name the following elements in order

    Ti, Te, Tl & At 

    Answer

    Titanium, Tellurium, Thallium and Astatine

     

    Isotopes

    Exercise \(\PageIndex{3.a}\)

    Write the symbol for each of the following ions:

    1. the ion with a 1+ charge, atomic number 55, and mass number 133
    2. the ion with 54 electrons, 53 protons, and 74 neutrons
    3. the ion with atomic number 15, mass number 31, and a 3− charge
    4. the ion with 24 electrons, 30 neutrons, and a 3+ charge

    (see 

    Answer a

    133Cs+

    Answer b

    127I

    Answer c

    31P3+

    Answer d

    57Co3+

     

    Exercise \(\PageIndex{3.b}\)

    The following are properties of isotopes of two elements that are essential in our diet. Determine the number of protons, neutrons and electrons in each and name them.

    1. atomic number 26, mass number 58, charge of 2+
    2. atomic number 53, mass number 127, charge of 1−
    Answer a

    Iron +2 cation, 26 protons, 24 electrons, and 32 neutrons (it is actually the ferrous ion, section 4.5.3.1.1.2)

    Answer b

    Iodine -1 anion, 53 protons, 54 electrons, and 74 neutrons (it is actually the iodide ion, section 4.5.3.1)

     

    Exercise \(\PageIndex{3.c}\)

    Give the number of protons, electrons, and neutrons in neutral atoms of each of the following isotopes:

    1. \(_{3}^{7}\textrm{Li}\)
    2. \(_{52}^{125}\textrm{Te}\)
    3. \(_{47}^{109}\textrm{Ag}\)
    4. \(_{7}^{15}\textrm{N}\)
    5. \(_{15}^{31}\textrm{P}\)
    Answer a

    3 protons, 3 electrons, 4 neutrons 

    Answer b

    52 protons, 52 electrons, 73 neutrons 

    Answer c

    47 protons, 47 electrons, 62 neutrons 

    Answer d

    7 protons, 7 electrons, 8 neutrons 

    Answer e

    15 protons, 15 electrons, 16 neutrons

     

    Exercise \(\PageIndex{3.d}\)

    Write a symbol for each of the following neutral isotopes. Include the atomic number and mass number for each.

    1. the alkali metal with 11 protons and a mass number of 23
    2. the noble gas element with and 75 neutrons in its nucleus and 54 electrons in the neutral atom
    3. the isotope with 33 protons and 40 neutrons in its nucleus
    4. the alkaline earth metal with 88 electrons and 138 neutrons
    Answer a

    \(_{11}^{23}\textrm{Na}\)

    Answer b

    \(_{54}^{129}\textrm{Xe}\)

    Answer c

    \(_{33}^{73}\textrm{As}\)

    Answer d

    \(_{88}^{226}\textrm{Ra}\)

     

    Isotopic Abundance

    Exercise \(\PageIndex{4.a}\)

    Average atomic masses listed by IUPAC are based on a study of experimental results. Bromine has two isotopes 79Br and 81Br, whose masses (78.9183 and 80.9163 amu) and abundances (50.69% and 49.31%) were determined in earlier experiments. Calculate the average atomic mass of bromine based on these experiments.

    Answer
    Isotope Mass Percent Abundance Fraction
    79Br 78.9183amu 50.69% 0.5069
    81Br 80.9163 amu 49.31% 0.4931


    \[{X_A}{(m_A)} +{X_B}{(m_B)} = {m_{ave}}\]

    \[{X_{79Br}}{(m_{79Br})} +{X_{81Br}}{(m_{81Br})} = {m_{ave}}\]

    \[{0.5069}{(78.9183amu)} +{0.4931}{(80.9163 amu)} = {m_{ave}}\]

    \[{m_{ave}}=79.904 amu\]

     

    Exercise \(\PageIndex{4.b}\)

    Average atomic masses listed by IUPAC are based on a study of experimental results. The average atomic mass of Copper is 63.546 amu. Copper has two isotopes 63Cu and 65Cu. The mass of 63Cu was determined in an earlier experiment and found to be 62.930 amu. The abundance of 63Cu was found to be 69.17%. Calculate the mass and abundance of 65Cu.

    Answer
    Isotope Mass Percent Abundance Fraction
    63Cu 62.930 amu 69.17% 0.6917
    65Cu \(m_B\nonumber\) \(%_B\nonumber\) \(X_B\nonumber\)

    \[X_A + X_B=1\]

    \[X_B=1-X_A \]

    \[X_B=1-0.6917=0.3083=30.83% \]

    \[{X_A}{(m_A)} +{X_B}{(m_B)} = {m_{ave}}\]

    \[m_B=\frac{m_{ave}-X_A(m_A)}{X_B}\]

    \[m_B=\frac{63.546amu-0.6917(62.930 amu)}{0.3083}\]

    \[m_B= 64.928amu\]

     

    Exercise \(\PageIndex{4.c}\)

    Average atomic masses listed by IUPAC are based on a study of experimental results. The average atomic mass of Gallium is 69.723 amu. Gallium has two isotopes 69Ga and 71Ga, whose masses (68.9257 and 70.9249 amu) were determined in earlier experiments. What is the natural abundance of each isotope?

    Answer
    Isotope Mass Fraction
    69Ga 68.9257 amu \(X_A\nonumber\)
    71Ga 70.9249 amu \(X_B\nonumber\)

    \[{X_A}{(m_A)} +{X_B}{(m_B)} = {m_{ave}}\]

    \[X_A + X_B=1\]

    \[X_B=1-X_A \]

    \[{X_A}{(m_A)} +{1-X_A}{(m_B)} = {m_{ave}}\]

    \[{X_A}=\frac{m_{ave}-m_B}{m_A-m_B}\]

    \[{X_A}=\frac{69.723 amu-70.9249amu}{68.9257amu-70.9249amu}\]

    \[{X_A}=0.6012\]

    \[X_B=1-X_A \]

    \[X_B=1-0.6012=0.3988 \]

    The natural abundance of 69Ga is 60.12% and of 71Ga is 39.88%

     

    Exercise \(\PageIndex{4.d}\)

    In an alternate universe on the planet Htrae, the element Minebro has two isotopes 79Mr and 81Mr, whose masses (78.9183 and 80.9163 amu) and abundances (49.31% and 50.69%) were determined in earlier experiments. Calculate the average atomic mass of Minebro based on these experiments.

    Answer
    Isotope Mass Percent Abundance Fraction
    79Br 78.9183amu 49.31% 0.4931
    81Br 80.9163 amu 50.69% 0.5069


    \[{X_A}{(m_A)} +{X_B}{(m_B)} = {m_{ave}}\]

    \[{X_{79Br}}{(m_{79Br})} +{X_{81Br}}{(m_{81Br})} = {m_{ave}}\]

    \[{0.4931}{(78.9183amu)} +{0.5069}{(80.9163 amu)} = {m_{ave}}\]

    \[{m_{ave}}= 79.931amu\]

     

    Exercise \(\PageIndex{4.e}\)

    In an alternate universe on the planet Htrae, the element Robber has an average atomic mass of 64.494 amu. Robber has two isotopes 63Ru and 65Ru. The mass of 63Ru was determined in an earlier experiment and found to be 62.930 amu. The abundance of 63Ru was found to be 21.72%. Calculate the mass and abundance of 65Ru.

    Answer
    Isotope Mass Percent Abundance Fraction
    63Cu 62.930 amu 21.72% 0.2172
    65Cu \(m_B\nonumber\) \(%_B\nonumber\) \(X_B\nonumber\)

    \[X_A + X_B=1\]

    \[X_B=1-X_A \]

    \[X_B=1-0.2172=0.7828=78.28% \]

    \[{X_A}{(m_A)} +{X_B}{(m_B)} = {m_{ave}}\]

    \[m_B=\frac{m_{ave}-X_A(m_A)}{X_B}\]

    \[m_B=\frac{64.494amu-0.2172(62.930 amu)}{0.7828}\]

    \[m_B= 64.928\]

     

     

    Periodic Table

    Exercise \(\PageIndex{5.a}\)

    Using the periodic table, classify each of the following elements as a metal or a nonmetal, and then further classify each as a main-group (representative) element, transition metal, or inner transition metal:

    1. uranium
    2. bromine
    3. strontium
    4. neon
    5. gold
    6. americium
    7. rhodium
    8. sulfur
    9. carbon
    10. potassium
    Answer a

    metal, inner transition metal

    Answer b

    nonmetal, representative element

    Answer c

    metal, representative element

    Answer d

    nonmetal, representative element

    Answer e

    metal, transition metal

    Answer f

    metal, inner transition metal

    Answer g

    metal, transition metal

    Answer h

    nonmetal, representative element

    Answer i

    nonmetal, representative element

    Answer j

    metal, representative element

     

    Exercise \(\PageIndex{5.b}\)

    Using the periodic table, identify the lightest and heaviest member of each of the following groups:

    1. noble gases
    2. alkaline earth metals
    3. alkali metals
    4. chalcogens
    Answer a

    He, Og

    Answer b

    Be, Ra

    Answer c

    Li, Fr

    Answer d

    O, Lv

     

    Exercise \(\PageIndex{5.c}\)

    Use the periodic table to give the name and symbol for each of the following elements:

    1. the noble gas in the same period as germanium
    2. the alkaline earth metal in the same period as selenium
    3. the halogen in the same period as lithium
    4. the chalcogen in the same period as cadmium
    Answer a

    krypton, Kr

    Answer b

    calcium, Ca

    Answer c

    fluorine, F

    Answer d

    tellurium, Te

    Robert E. Belford (University of Arkansas Little Rock; Department of Chemistry). The breadth, depth and veracity of this work is the responsibility of Robert E. Belford, rebelford@ualr.edu. You should contact him if you have any concerns. This material has both original contributions, and content built upon prior contributions of the LibreTexts Community and other resources, including but not limited to:

    • Liliane Poirot

    3: Atoms and Elements is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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