1. 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?
2. How are atoms of the same element the same? How are atoms of the same element different?
3. Write the isotope symbols for H-1, H-2, and H-3. Sketch each atom showing protons, neutrons, and electrons.
4. A rare isotope of helium has a single neutron in its nucleus. Write the complete atomic symbol of this isotope.
5. Use its place on the periodic table to determine if indium, In, atomic number 49, is a metal or a nonmetal.
6. 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?
7. Americium-241 is a crucial part of many smoke detectors. How many neutrons are present in its nucleus?
8. Potassium-40 is a radioactive isotope of potassium that is present in the human body. How many neutrons are present in its nucleus?
9. Determine the atomic mass of ruthenium from the given abundance and mass data.
   

   Isotope	Abundance	Mass
   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

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

    Isotope	Abundance	Mass
    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

11. One atomic mass unit has a mass of 1.6605 × 10⁻²⁴ g. What is the mass of one atom of sodium?
12. One atomic mass unit has a mass of 1.6605 × 10⁻²⁴ g. What is the mass of one atom of uranium?
13. One atomic mass unit has a mass of 1.6605 × 10⁻²⁴ g. What is the mass of one molecule of H₂O?
14. One atomic mass unit has a mass of 1.6605 × 10⁻²⁴ g. What is the mass of one molecule of PF₅?
15. From their positions on the periodic table, will Cu and I form a molecular compound or an ionic compound?
16. From their positions on the periodic table, will N and S form a molecular compound or an ionic compound?
17. The uranyl cation has the formula UO₂²⁺. Propose formulas and names for the ionic compounds between the uranyl cation and F⁻, SO₄²⁻, and PO₄³⁻.
18. The permanganate anion has the formula MnO₄⁻. Propose formulas and names for the ionic compounds between the permanganate ion and K⁺, Ca²⁺, and Fe³⁺.
19. Write the electron configuration for Ca.
20. Write the electron configuration for Rb.
21. Write the electron configuration for Ge.
22. Write the electron configuration for Ga.

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

3.

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 5. It is a metal.

7. 146 neutrons

9. 101.065 u

11. 3.817 × 10⁻²³ g

13. 2.991 × 10⁻²³ g

15. Ionic compound

17. Uranyl fluoride, UO₂F₂; uranyl sulfate, UO₂SO₄; uranyl phosphate, (UO₂)₃(PO₄)₂

19. 1s², 2s², 2p⁶, 3s², 3p⁶, 4s², or [Ar] 4s²

21. 1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p², or [Ar] 4s², 3d¹⁰, 4p²