3: Atoms and Elements

Last updated
Save as PDF

Page ID: 279973

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)

\( \newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\)

( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\)

\( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)

\( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\)

\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)

\( \newcommand{\Span}{\mathrm{span}}\)

\( \newcommand{\id}{\mathrm{id}}\)

\( \newcommand{\Span}{\mathrm{span}}\)

\( \newcommand{\kernel}{\mathrm{null}\,}\)

\( \newcommand{\range}{\mathrm{range}\,}\)

\( \newcommand{\RealPart}{\mathrm{Re}}\)

\( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)

\( \newcommand{\Argument}{\mathrm{Arg}}\)

\( \newcommand{\norm}[1]{\| #1 \|}\)

\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)

\( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\AA}{\unicode[.8,0]{x212B}}\)

\( \newcommand{\vectorA}[1]{\vec{#1}} % arrow\)

\( \newcommand{\vectorAt}[1]{\vec{\text{#1}}} % arrow\)

\( \newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

\( \newcommand{\vectorC}[1]{\textbf{#1}} \)

\( \newcommand{\vectorD}[1]{\overrightarrow{#1}} \)

\( \newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}} \)

\( \newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}} \)

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)

\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)

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:

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

atomic number 26, mass number 58, charge of 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:

\(_{3}^{7}\textrm{Li}\)
\(_{52}^{125}\textrm{Te}\)
\(_{47}^{109}\textrm{Ag}\)
\(_{7}^{15}\textrm{N}\)
\(_{15}^{31}\textrm{P}\)

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.

the alkali metal with 11 protons and a mass number of 23
the noble gas element with and 75 neutrons in its nucleus and 54 electrons in the neutral atom
the isotope with 33 protons and 40 neutrons in its nucleus
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
⁷⁹Mr	78.9183amu	49.31%	0.4931
⁸¹Mr	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 ⁶³Ro and ⁶⁵Ro. The mass of ⁶³Ro was determined in an earlier experiment and found to be 62.930 amu. The abundance of ⁶³Ro was found to be 21.72%. Calculate the mass and abundance of ⁶⁵Ro.

Answer

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

\[X_A + X_B=1\]

\[X_B=1-X_A \]

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

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

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

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

\[m_B= 64.928\]

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:

uranium
bromine
strontium
neon
gold
americium
rhodium
sulfur
carbon
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:

noble gases
alkaline earth metals
alkali metals
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:

the noble gas in the same period as germanium
the alkaline earth metal in the same period as selenium
the halogen in the same period as lithium
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

Search

Text Color

Text Size

Margin Size

Font Type