Atoms, Molecules, and Ions

In what way are isotopes of a given element always different? In what way(s) are they always the same?

Write the symbol for each of the following ions: (a) the ion with a \(1 + \) charge, atomic number \(55,\) and mass number \(133\)(b) the ion with \(54\) electrons, \(53\) protons, and \(74\) neutrons (c) the ion with atomic number\(15,\) mass number \(31,\) and a \(3 - \) charge (d) the ion with \(24\) electrons, \(30\) neutrons, and a \(3 + \)charge

An element has the following natural abundance, and isotopic masses; 90.90% abundance with 19.99 amu, 0.26% abundance with 20.99 amu, and 8.82% abundance with 21.99 amu. Calculate the average atomic mass of this element.

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 abundance (50.69% and 49.31%) were determined in earlier experiments. Calculate the average atomic mass of bromine based on these experiments.

The average atomic masses of some elements may vary, depending upon the sources of their ores. Naturally occurring, the boron consists of two isotopes with accurately known masses ( ¹⁰B, 10.0129 amu and ¹¹B, 11.0931 amu). The actual atomic mass of boron can vary from 10.807 to 10.819, depending on whether the mineral source is from Turkey or the United States. Calculate the percent abundance leading to the two values of the average atomic masses of boron from these two countries.

Explain why the symbol for an atom of the element oxygen and the formula for a molecule of oxygen differ.

Determine the empirical formula for the following compounds:

a) caffeine, C₆H₁₀N₄O₂ 

b) fructose, C₁₂H₂₂O₁₁

c) hydrogen peroxide, H₂O₂

d) glucose, C₆H₁₂O₆

e) ascorbic acid (vitamin C), C₆H₈O₆

Determine the empirical formulas for the following compounds.

a. acetic acid, C₂H₄O₂

b. citric acid, C₆H₈O₇ 

c. hydrazine, N₂H₄ 

d. nicotine, C₁₀H₁₄N₂

e. butane, C₄H₁₀

Write the empirical formula for the following compounds:

Open the Build a Molecule simulation (http://openstaxcollege.org/l/16molbuilding) and select the “Larger Molecules” tab. Select an appropriate atoms “Kit” to build a molecule with two carbon and six hydrogen atoms. Drag atoms into the space above the “Kit” to make a molecule. A name will appear when you have made an actual molecule that exists (even if it is not the one you want). You can use the scissors tool to separate atoms if you would like to change the connections. Click on “3D” to see the molecule, and look at both the space-filling and ball and-stick possibilities. (a) Draw the structural formula of this molecule and state its name. (b) Can you arrange these atoms in any way to make a different compound?

Write a symbol for each of the following neutral isotopes. Include the atomic number and mass number for each. (a) the chalcogen with a mass number of \({\bf{125}}\) (b) the halogen whose longest-lived isotope is radioactive (c) the noble gas, used in lighting, with \({\bf{10}}\) electrons and \({\bf{10}}\) neutrons (d) the lightest alkali metal with three neutrons

Using the periodic table, predict whether the following chlorides are ionic or covalent: \(KCl,{\rm{ }}NC{l_3},{\rm{ }}ICl,{\rm{ }}MgC{l_2},{\rm{ }}PC{l_5},\)and \(CC{l_4}\). 

Using the periodic table, predict whether the following chlorides are ionic or covalent:\(SiC{l_4},PC{l_3},CaC{l_2},CsCl,CuC{l_2}{\rm{ and }}CrC{l_3}.\)

For each of the following pairs of ions, write the symbol for the formula of the compound they will form:

1. \(C{a^{2 + }},{S^{2 - }}\)
2. \(NH_4^ + ,SO_4^{2 - }\)
3. \(A{l^{3 + }},B{r^ - }\)
4. \(N{a^ + },HPO_4^{2 - }\)
5. \(M{g^{2 + }},PO_4^{3 - }\)

Question : Write the formulas of the following compounds: 

(a) lithium carbonate 

(b) sodium perchlorate 

(c) barium hydroxide 

(d) ammonium carbonate 

(e) sulfuric acid 

(f) calcium acetate 

(g) magnesium phosphate 

(h) sodium sulfite

An ion of platinum has a mass number of 195 and contains 74 electrons. How many protons and neutrons does it contain and what is it’s charge ? 

In the following drawing, the green spheres represent atoms of a certain element. The purple spheres represent atoms of another element. If the spheres touch, they are part of a single unit of a compound. Does the following chemical change represented by these symbols violate any of the ideas of Dalton’s atomic Theory? If so, which one?

A sample of magnesium is found to contain 78.70% of 24Mg atoms (mass 23.98 amu), 10.13% of 25Mg atoms (mass 24.99 amu), and 11.17% of 26Mg atoms (mass 25.98 amu). Calculate the average mass of a Mg atom.

_{Naturally occurring copper consists of 63Cu (mass 62.9296 amu) and 65Cu (mass 64.9278 amu), with an average mass of 63.546 amu. What is the percent composition of Cu in terms of these two isotopes?}

Give the group name for each of the following elements: (a) krypton (b) selenium (c) barium (d) lithium

In the following drawing, the green spheres represent atoms of a certain element. The purple spheres represent atoms of another element. If the spheres of different elements touch, they are part of a single unit of a compound. The following chemical change represented by these spheres may violate one of the ideas of Dalton’s atomic theory. Which one?

Which postulate of Dalton’s theory is consistent with the following observation concerning the weights of reactants and products? When 100 grams of solid calcium carbonate is heated, 44 grams of carbon dioxide and 56 grams of calcium oxide are produced.

Identify the postulate of Dalton’s theory that is violated by the following observations: 59.95% of one sample of titanium dioxide is titanium; 60.10% of a different sample of titanium dioxide is titanium.

Samples of compound X, Y, and Z are analyzed, with results shown here.

Do these data provide example(s) of the law of definite proportions, the law of multiple proportions, neither, or both? What do these data tell you about compounds X, Y, and Z?

The existence of isotopes violates one of the original ideas of Dalton’s atomic theory. Which one?

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

Predict and test the behaviour of α particles fired at a Rutherford atom model. 

(a) Predict the paths taken by α particles that are fired at atoms with a Rutherford atom model structure. Explain why you expect the α particles to take these paths. 

(b) If α particles of higher energy than those in (a) are fired at Rutherford atoms, predict how their paths will differ from the lower-energy α particle paths. Explain your reasoning. 

(c) Predict how the paths taken by the α particles will differ if they are fired at Rutherford atoms of elements other than gold. What factor do you expect to cause this difference in paths, and why? 

(d) Now test your predictions from (a), (b), and (c). 

Open the Rutherford Scattering simulation (http://openstaxcollege.org/l/16PhetScatter) and select the “Rutherford Atom” tab. Due to the scale of the simulation, it is best to start with a small nucleus, so select “20” for both protons and neutrons, “min” for energy, show traces, and then start firing α particles. Does this match your prediction from (a)? If not, explain why the actual path would be that shown in the simulation. Pause or reset, set energy to “max,” and start firing α particles. Does this match your prediction from (b)? If not, explain the effect of increased energy on the actual path as shown in the simulation. Pause or reset, select “40” for both protons and neutrons, “min” for energy, show traces, and fire away. Does this match your prediction from (c)? If not, explain why the actual path would be that shown in the simulation. Repeat this with larger numbers of protons and neutrons. What generalization can you make regarding the type of atom and effect on the path of α particles? Be clear and specific.

Open theBuild an Atom simulation (http://openstaxcollege.org/l/16PhetAtomBld)and click on the

Atom icon.

State the numbers of protons, neutrons, and electrons in your atom, as well as  the net charge and mass number.

Open theBuild an Atom simulation (http://openstaxcollege.org/l/16PhetAtomBld)(a) Drag protons, neutrons, and electrons onto the atom template to make a neutral atom of Oxygen-16 and give theisotope symbol for this atom.(b) Now add two more electrons to make an ion and give the symbol for the ion you have created.

Determine the number of protons, neutrons, and electrons in the following isotopes that are used in medical diagnoses: 

(a) atomic number 9_, mass number 18_, charge of 1^-

b) atomic number 43, mass number 99, charge of 7⁺

(c) atomic number 53, atomic mass number 131, charge of 1^-

(d) atomic number 81, atomic mass number 201, charge of 1⁺

(e) Name the elements in parts (a), (b), (c), and (d)

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

\(\begin{aligned}{\underline{\phantom{xx}}}\begin{aligned}{{}{\underline{\phantom{xx}}}}{\left( a \right){\rm{ }}{\underline{\phantom{xx}}}_5^{10}B}\\{\left( b \right){\rm{ }}{\underline{\phantom{xx}}}_{80}^{199}Hg}\\{\left( c \right){\rm{ }}{\underline{\phantom{xx}}}_{29}^{63}Cu}\\{\left( d \right){\rm{ }}{\underline{\phantom{xx}}}_6^{13}C}\end{aligned}\\\left( e \right){\rm{ }}{\underline{\phantom{xx}}}_{34}^{77}Se\end{aligned}\)

Give the number of protons, electrons, and neutrons in neutral atoms of each of the following isotopes:\(\begin{aligned}{\underline{\phantom{xx}}}\left( a \right){\rm{ }}{\underline{\phantom{xx}}}_3^7Li{\rm{ }}\\\left( b \right){\rm{ }}{\underline{\phantom{xx}}}_{52}^{125}Te{\rm{ }}\\\left( c \right){\rm{ }}{\underline{\phantom{xx}}}_{47}^{109}Ag{\rm{ }}\\\left( d \right){\rm{ }}{\underline{\phantom{xx}}}_7^{15}N{\rm{ }}\\\left( e \right){\rm{ }}{\underline{\phantom{xx}}}_{15}^{31}P\end{aligned}\)

Click on the site (http://openstaxcollege.org/l/16PhetAtomMass) and select the “Mix Isotopes” tab, hide the “Percent Composition” and “Average Atomic Mass” boxes, and then select the element boron.

(a) Write the symbols of the isotopes of boron that are shown as naturally occurring in significant amounts.

(b) Predict the relative amounts (percentages) of these boron isotopes found in nature. Explain the reasoning behind your choice.

(c) Add isotopes to the black box to make a mixture that matches your prediction in (b). You may drag isotopes fromtheir bins or click on “More” and then move the sliders to the appropriate amounts.

(d) Reveal the “Percent Composition” and “Average Atomic Mass” boxes. How well does your mixture match withyour prediction? If necessary, adjust the isotope amounts to match your prediction.

(e) Select “Nature’s” mix of isotopes and compare it to your prediction. How well does your prediction comparewith the naturally occurring mixture? Explain. If necessary, adjust your amounts to make them match “Nature’s”amounts as closely as possible.

Variations in average atomic mass may be observed for elements obtained from different sources. Lithium provides an example of this. The isotopic composition of lithium from naturally occurring minerals is 7.5% ⁶Li and 92.5% ⁷Li, which have masses of 6.01512 amu and 7.01600 amu, respectively. A commercial source of lithium, recycled from a military source, was 3.75% ⁶Li (and the rest ⁷Li). Calculate the average atomic mass values for each of these two sources.  

The ¹⁸O: ¹⁶O abundance ratio in some meteorites is greater than that used to calculate the average atomic mass of oxygen on earth. Is the average mass of an oxygen atom in these meteorites greater than, less than, or equal to that of a terrestrial oxygen atom?

Write the molecular and empirical formulas of the following compounds:

a) 

(b) 

(c) 

(d) 

Use the Build a Molecule simulation (http://openstaxcollege.org/l/16molbuilding) to repeat Exercise 2.34, but build a molecule with two carbons, six hydrogens, and one oxygen. (a) Draw the structural formula of this molecule and state its name. (b) Can you arrange these atoms to make a different molecule? If so, draw its structural formula and state its name. (c) How are the molecules drawn in (a) and (b) the same? How do they differ? What are they called (the type of relationship between these molecules, not their names)?

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

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

(a) noble gases

(b) alkaline earth metals 

(c) alkali metals 

(d) chalcogens

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

(a) Alkali metals

(b) Chalcogens

(c) Noble gases

(d) Alkaline earth metals

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

 (a) The Nobel gas in the same period as Germanium.

 (b) The Alkaline earth metal in the same period as selenium.

 (c)  The Halogen in the same period as lithium.

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

 (a) the halogen in the same period as the alkali metal with 11 protons 

(b) the alkaline earth metal in the same period with the neutral noble gas with 18 electrons 

(c) the noble gas in the same row as an isotope with 30 neutrons and 25 protons 

(d) the noble gas in the same period as gold

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

(a) the alkali metal with 11 protons and a mass number of 23 

(b) the noble gas element with 75 neutrons in its nucleus and 54 electrons in the neutral atom 

(c) the isotope with 33 protons and 40 neutrons in its nucleus 

(d) the alkaline earth metal with 88 electrons and 138 neutrons

For each of the following compounds, state whether it is ionic or covalent. If it is ionic, write the symbols for the ions involved:

1. NF₃
2. BaO
3. (NH₄)₂CO₃
4. Sr(H₂PO₄)₂
5. IBr
6. Na₂O

For each of the following compounds, state whether it is ionic or covalent, and if it is ionic, write the symbols for the ions involved:

1. \(KCl{O_4}\)
2. \(Mg{\left( {{C_2}{H_3}{O_2}} \right)_2}\)
3. \({H_2}S\)
4. \(A{g_2}S\)
5. \({N_2}C{l_4}\)
6. \(Co{\left( {N{O_3}} \right)_2}\)

Question : Name the following compounds:

1. NaF
2. Rb₂O
3. BCl₃
4. H₂Se
5. P₄O₆
6. ICl₃

Question: Write the formulas of the following compounds: 

(a) rubidium bromide 

(b) magnesium selenide 

(c) sodium oxide 

(d) calcium chloride 

(e) hydrogen fluoride 

(f) gallium phosphide 

(g) aluminum bromide 

(h) ammonium sulfate

Question: Write the formulas of the following compounds: 

(a) chlorine dioxide 

(b) dinitrogen tetraoxide

(c) potassium phosphide 

(d) silver(I) sulfide 

(e) aluminum nitride 

(f) silicon dioxide

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

Predict and test the behavior of α particles fired at a “plum pudding” model atom.

(a) Predict the paths taken by α particles that are fired at atoms with a Thomson’s plum pudding model structure. Explain why you expect the α particles to take these paths.

(b) If α particles of higher energy than those in (a) are fired at plum pudding atoms, predict how their paths will differ from the lower-energy α particle paths. Explain your reasoning.

(c) Now test your predictions from (a) and (b). Open the Rutherford Scattering simulation (http://openstaxcollege.org/l/16PhetScatter) and select the “Plum Pudding Atom” tab. Set “Alpha Particles Energy” to “min,” and select “show traces.” Click on the gun to start firing α particles. Does this match your prediction from (a)? If not, explain why the actual path would be that shown in the simulation. Hit the pause button, or “Reset All.” Set “Alpha Particles Energy” to “max,” and start firing α particles. Does this match your prediction from (b)? If not, explain the effect of increased energy on the actual paths as shown in the simulation.