How the model of the atom changed

Answer Key - Grade 10 Science Worksheet - Building Confidence

Circle the best answer, or write your answer on the line.

1. Read this first

   Hydrogen's energy levels in Bohr's model (from E = −13.6 ÷ n²)

   level n	energy (eV)
   1	−13.60
   2	−3.40
   3	−1.51
   4	−0.85

2. 1.

   An electron in hydrogen drops from level n = 3 to n = 2 and gives off one photon carrying the energy it lost. How much energy does the photon carry, to 0.01 eV, Ari?

   1.89 eV
3. 2.

   An electron in hydrogen drops from level n = 2 to n = 1 and gives off one photon carrying the energy it lost. How much energy does the photon carry, to 0.01 eV, Bo?

   10.2 eV
4. 3.

   An electron in hydrogen drops from level n = 4 to n = 3 and gives off one photon carrying the energy it lost. How much energy does the photon carry, to 0.01 eV, Esme?

   0.66 eV

5. Card

   Atom models and the evidence behind them. 1808, Dalton: atoms are solid, indivisible spheres. 1897, evidence: a beam in a vacuum tube bends toward a positive plate, so it carries negative particles (electrons) that come out of atoms. 1904, Thomson: a positive sphere with electrons dotted through it. 1909 to 1911, evidence: in a gold-foil test, most alpha particles pass straight through and a very few bounce back. 1911, Rutherford: a tiny, dense, positive nucleus with electrons around it. 1913, evidence: hydrogen gas gives off light of only a few colors. 1913, Bohr: electrons on set energy levels.

6. 4.

   Jun reads the card. Which change to the atom model came right after the 1897 beam-bending evidence?

   • Electrons were given set energy levels around the nucleus
   • A tiny, dense nucleus was added at the center of the atom
   • Electrons were placed inside atoms, which were no longer indivisible
7. 5.

   Dalton called atoms indivisible. Luz reads the card. Which evidence first contradicted that?

   • The 1897 beam, because electrons came out of atoms
   • The hydrogen light of 1913, because the colors were few
   • The gold-foil test, because particles bounced back from atoms
8. 6.

   Thomson made his beam in tubes with different gases and cathodes of different metals. The beam was always the same. What did that suggest, Milo?

   • Each gas makes its own kind of electron
   • Electrons are a part of every kind of atom
   • Only the gas in the tube contains electrons
9. 7.

   In a described run (example data), 7,999 of 8,000 alpha particles pass nearly straight through foil and 1 bounces back. What does that say about the positive charge, Noah?

   • It fills the whole atom, so each particle meets it
   • It is spread evenly, but the foil was too thin to show it clearly
   • It sits in a tiny region, so a particle rarely comes near it
10. 8.

    Hydrogen gas lit by electricity gives off only a few colors, not a full rainbow. Which idea fits that best, Pia?

    • Electrons can have any energy, so every color is possible
    • Electrons can have only certain energies, so only certain colors are possible
    • The nucleus gives off light as it slowly turns

11. Chlorine atoms by mass (rounded isotope data)

    mass of atom	share of atoms
    35	75.8%
    37	24.2%

12. 9.

    Dalton said all atoms of one element have the same mass. What does the table show about that idea, Tala?

    • It holds: 75.8% of atoms share one mass, so the others must be errors
    • It fails: chlorine has atoms of two different masses
    • It holds: both masses round to about 36, the same mass
13. 10.

    Water has 1.0 g of hydrogen per 8.0 g of oxygen; hydrogen peroxide has 1.0 g per 16.0 g. Zee says they cannot be built from the same atoms. How would Dalton reply?

    • Both are hydrogen and oxygen atoms in different whole-number counts, with oxygen doubled
    • He would agree, since a given pair of elements can form just one compound
    • He would say the masses must be equal if the atoms are the same, so peroxide is impossible