2.E: Atomic Structure (Exercises)

2.1-2.4: Basic Atomic Theory

1. List the three statements that make up the modern atomic theory.

2. Explain how atoms are composed.

3. Which is larger, a proton or an electron?

4. Which is larger, a neutron or an electron?

5. What are the charges for each of the three subatomic particles?

6. Where is most of the mass of an atom located?

7. Sketch a diagram of a boron atom, which has five protons and six neutrons in its nucleus.

8. Sketch a diagram of a helium atom, which has two protons and two neutrons in its nucleus.

9. Define atomic number. What is the atomic number for a boron atom?

10. What is the atomic number of helium?

11. Define isotope and give an example.

12. What is the difference between deuterium and tritium?

13. Which pair represents isotopes?

1. \[_{2}^{4}\textrm{He} \, and\: \, _{2}^{3}\textrm{He}\]
2. \[_{26}^{56}\textrm{Fe} \, and\: \, _{25}^{56}\textrm{Mn}\]
3. \[_{14}^{28}\textrm{Si} \, and\: \, _{15}^{31}\textrm{P}\]

14. Which pair represents isotopes?

1. \[_{20}^{40}\textrm{Ca} \, and\: \, _{19}^{40}\textrm{K}\]
2. \[_{26}^{56}\textrm{Fe} \, and\: \, _{28}^{56}\textrm{Fe}\]
3. \[_{92}^{238}\textrm{U} \, and\: \, _{92}^{235}\textrm{U}\]

15. Give complete symbols of each atom, including the atomic number and the mass number.

    a. an oxygen atom with 8 protons and 8 neutrons
    b. a potassium atom with 19 protons and 20 neutrons
    c. a lithium atom with 3 protons and 4 neutron

16. Give complete symbols of each atom, including the atomic number and the mass number.
    
    a. a magnesium atom with 12 protons and 12 neutrons
    b. a magnesium atom with 12 protons and 13 neutrons
    c. a xenon atom with 54 protons and 77 neutron
17. Americium-241 is an isotope used in smoke detectors. What is the complete symbol for this isotope?

18. Carbon-14 is an isotope used to perform radioactive dating tests on previously living material. What is the complete symbol for this isotope?

19. Give atomic symbols for each element.

    a. sodium
    b. argon
    c. nitrogen
    d. radon

20. Give atomic symbols for each element.
    a. silver
    b. gold
    c. mercury
    d. iodine
21. Give the name of the element.
    a.Si
    b. Mn
    c. Fe
    d. Cr
22. Give the name of the element.
    a. F
    b. Cl
    c. Br
    d. I

Answers

1. All matter is composed of atoms; atoms of the same element are the same, and atoms of different elements are different; atoms combine in whole-number ratios to form compounds.
2.  

3. A proton is larger than an electron.

4. proton: 1+; electron: 1−; neutron: 0
5.  
6. In the nucleus of the atom
7. 
8.  
9. The atomic number is the number of protons in a nucleus. Boron has an atomic number of five.
10.  
11. Isotopes are atoms of the same element but with different numbers of neutrons. \[_{1}^{1}\textrm{H} \, and\: \, _{1}^{2}\textrm{H}\]
12.  
13.  

1. isotopes
2. not isotopes
3. not isotopes

 

14.  
15.  

1. \[_{8}^{16}\textrm{O}\]
2. \[_{19}^{39}\textrm{K}\]
3. \[_{3}^{7}\textrm{Li}\]

16.  

17. \[_{95}^{241}\textrm{Am}\] 

     
18.  
19. 1. Na
    2. Ar
    3. N
    4. Rn
20.  
21. 1. silicon
    2. manganese
    3. iron
    4. chromium

2.5-2.7: Ions and Groups on the Periodic Table

1. How many protons and electrons are in each of the following atoms or ions?

1. Mg
2. Mg²⁺
3. P
4. P^3-

2. Explain how an ion is formed. How can you know the charge of an ion?

3. For each of the following determine if it is a metal or non-metal?

1. Oxygen, O
2. Sodium, Na
3. Phosphorus, P
4. Potassium, K

4. What is the name of the periodic table "Group" for each of the following elements?

1. Chlorine, Cl
2. Argon, Ar
3. Sodium, Na
4. Potassium, K

Answers

1.  

1. Mg, 12 protons, 12 electrons
2. Mg²⁺, 12 protons, 10 electrons
3. P, 15 protons, 15 electrons
4. P^3-, 15 protons, 18 electrons

2. Please explain in your own words.

3. a. non-metal

   b. metal

   c. non-metal

   d. metal

4. a. Halogen

   b. Noble Gas

   c. Alkaline Metals

   d. Alkaline Metals

2.8-2.9: Masses of Atoms and Molecules

1. Define atomic mass unit. What is its abbreviation?
2. Estimate the mass, in whole numbers, of each isotope.
   1. hydrogen-1
   2. hydrogen-3
   3. iron-56
3. Estimate the mass, in whole numbers, of each isotope.
   1. phosphorus-31
   2. carbon-14
   3. americium-241
4. Determine the atomic mass of each element, given the isotopic composition.
   1. lithium, which is 92.4% lithium-7 (mass 7.016 u) and 7.60% lithium-6 (mass 6.015 u)
   2. oxygen, which is 99.76% oxygen-16 (mass 15.995 u), 0.038% oxygen-17 (mass 16.999 u), and 0.205% oxygen-18 (mass 17.999 u)
5. Determine the atomic mass of each element, given the isotopic composition.
   1. neon, which is 90.48% neon-20 (mass 19.992 u), 0.27% neon-21 (mass 20.994 u), and 9.25% neon-22 (mass 21.991 u)
   2. uranium, which is 99.27% uranium-238 (mass 238.051 u) and 0.720% uranium-235 (mass 235.044 u)
6. How far off would your answer be from Exercise 5a if you used whole-number masses for individual isotopes of lithium?
7. How far off would your answer be from Exercise 6b if you used whole-number masses for individual isotopes of uranium?
8. 1. What is the atomic mass of an oxygen atom?
   2. What is the molecular mass of oxygen in its elemental form?
9. 1. What is the atomic mass of bromine?
   2. What is the molecular mass of bromine in its elemental form?
10. Determine the mass of each substance. (Add the masses of the individual elements.)
    1. F₂
    2. CO
    3. CO₂
11. Determine the mass of each substance.
    1. Kr
    2. KrF₄
    3. PF₅
12. Determine the mass of each substance. (Add the masses of the individual elements.)
    1. Na
    2. B₂O₃
    3. S₂Cl₂
13. Determine the mass of each substance.
    1. IBr₃
    2. N₂O₅
    3. CCl₄
14. Determine the mass of each substance.
    1. GeO₂
    2. IF₃
    3. XeF₆
15. Determine the mass of each substance.
    1. NO
    2. N₂O₄
    3. Ca

Answers

1. The atomic mass unit is defined as one-twelfth of the mass of a carbon-12 atom. Its abbreviation is u.
2. 1. 1
   2. 3
   3. 56
3.  
4. 1. 6.940 u
   2. 16.000 u
5.  
6. We would get 6.924 u.
7.  
8. 1. 15.999 u
   2. 31.998 u
9.  
10. 1. 37.996 u
    2. 28.010 u
    3. 44.009 u
11.  
12. 1. 22.990 u
    2. 69.619 u
    3. 135.036 u
13.  
14. 1. 104.64 u
    2. 183.898 u
    3. 245.281 u

Additional Exercises

1. How many electrons does it take to make the mass of one proton?
2. How many protons does it take to make the mass of a neutron?
3. Dalton’s initial version of the modern atomic theory says that all atoms of the same element are the same. Is this actually correct? Why or why not?
4. How are atoms of the same element the same? How are atoms of the same element different?
5. Give complete atomic symbols for the three known isotopes of hydrogen.
6. A rare isotope of helium has a single neutron in its nucleus. Write the complete atomic symbol of this isotope.
7. Use its place on the periodic table to determine if indium, In, atomic number 49, is a metal or a nonmetal.
8. Only a few atoms of astatine, At, atomic number 85, have been detected. On the basis of its position on the periodic table, would you expect it to be a metal or a nonmetal?
9. Americium-241 is a crucial part of many smoke detectors. How many neutrons are present in its nucleus?

10. Potassium-40 is a radioactive isotope of potassium that is present in the human body. How many neutrons are present in its nucleus?
11. Determine the atomic mass of ruthenium from the given abundance and mass data.

Ruthenium-96	5.54%	95.907 u
Ruthenium-98	1.87%	97.905 u
Ruthenium-99	12.76%	98.906 u
Ruthenium-100	12.60%	99.904 u
Ruthenium-101	17.06%	100.906 u
Ruthenium-102	31.55%	101.904 u
Ruthenium-104	18.62%	103.905 u

12. Determine the atomic mass of tellurium from the given abundance and mass data.

Tellurium-120	0.09%	119.904 u
Tellurium-122	2.55%	121.903 u
Tellurium-123	0.89%	122.904 u
Tellurium-124	4.74%	123.903 u
Tellurium-125	7.07%	124.904 u
Tellurium-126	18.84%	125.903 u
Tellurium-128	31.74%	127.904 u
Tellurium-130	34.08%	129.906 u

13. One atomic mass unit has a mass of 1.6605 × 10⁻²⁴ g. What is the mass of one atom of sodium?
14. One atomic mass unit has a mass of 1.6605 × 10⁻²⁴ g. What is the mass of one atom of uranium?

• One atomic mass unit has a mass of 1.6605 × 10⁻²⁴ g. What is the mass of one molecule of H₂O?
• One atomic mass unit has a mass of 1.6605 × 10⁻²⁴ g. What is the mass of one molecule of PF₅?
• From their positions on the periodic table, will Cu and I form a molecular compound or an ionic compound?

18. From their positions on the periodic table, will N and S form a molecular compound or an ionic compound?
19. Mercury is an unusual element in that when it takes a 1+ charge as a cation, it always exists as the diatomic ion.
    1. Propose a formula for the mercury(I) ion.
    2. What is the formula of mercury(I) chloride?
20. Propose a formula for hydrogen peroxide, a substance used as a bleaching agent. (Curiously, this compound does not behave as an acid, despite its formula. It behaves more like a classic nonmetal-nonmetal, molecular compound.)
21. The uranyl cation has the formula UO₂²⁺. Propose formulas and names for the ionic compounds between the uranyl cation and F⁻, SO₄²⁻, and PO₄³⁻.
22. The permanganate anion has the formula MnO₄⁻. Propose formulas and names for the ionic compounds between the permanganate ion and K⁺, Ca²⁺, and Fe³⁺.

Answers

1. about 1,800 electrons
2.  

3. It is not strictly correct because of the existence of isotopes.

4.  

5. \[_{1}^{1}\textrm{H},\; _{1}^{2}\textrm{H},\, and\; _{1}^{3}\textrm{H}\]

6.  

7. It is a metal.

8.  

9. 146 neutrons

10.  

11. 101.065 u

12.  

13. 3.817 × 10⁻²³ g

14.  

15. 2.991 × 10⁻²³ g

16.  

17. ionic

18.  
19. 1. Hg₂²⁺
    2. Hg₂Cl₂
20.  
21. uranyl fluoride, UO₂F₂; uranyl sulfate, UO₂SO₄; uranyl phosphate, (UO₂)₃(PO₄)₂