How the model of the atom changed

Answer Key - Grade 10 Science Worksheet - Challenge Me

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

1. 1.

   A hydrogen electron drops from n = 3 to n = 2 (rules on the sheet note). What wavelength does its photon have, to the nearest nm, Ari?

   656 nm
2. 2.

   A hydrogen electron drops from n = 4 to n = 1 (rules on the sheet note). What wavelength does its photon have, to the nearest nm, Bo?

   97 nm
3. 3.

   A hydrogen electron drops from n = 7 to n = 2 (rules on the sheet note). What wavelength does its photon have, to the nearest nm, Esme?

   397 nm
4. 4.

   The 1926 quantum model fits helium, which Bohr's model could not. What did it keep from Bohr and what did it drop, Jun?

   • Kept: set energy levels. Dropped: fixed circular paths, now clouds of likely positions
   • Kept: fixed circular paths. Dropped: set energy levels, since electrons can have any energy
   • Kept: nothing, since a new model must start over from entirely new evidence each time
5. 5.

   A student writes: Rutherford proved electrons orbit the nucleus like planets. Using the gold-foil results, what is the best verdict, Milo?

   • Supported: the large turns were caused by orbiting electrons pulling on the particles
   • Supported: a nucleus at the center means electrons must circle it like planets
   • Not supported: foil results locate the positive charge but not how electrons move
6. 6.

   A student says: Dalton's model was replaced, so none of it is still used. Which reply is best supported, Noah?

   • Right, since Dalton knew nothing about electrons or the nucleus when he wrote it
   • Right: once a model is replaced, each of its ideas is discarded with it
   • Overstated: whole-number ratios of atoms and rearranged atoms in reactions still hold
7. 7.

   Only 1 in 8,000 particles bounced back. In a short test of 800 particles, none did. Pia says that refutes the rate. What is the best reply?

   • Yes: the rate predicts about 1 bounce in 800, and none appeared in the test
   • No: at 1 in 8,000, 800 particles give about 0.1 bounces, so none is expected
   • Yes: only a test of 8,000 or more particles can ever check a rate like this
8. 8.

   A gold atom is about 3 × 10⁻¹⁰ m wide and its nucleus about 1.4 × 10⁻¹⁴ m (rounded). If the nucleus were a 1.4 cm marble, how wide would the atom be, Ren?

   • About 300 m
   • About 30 m
   • About 3,000 m

9. Read this first

   Which model explains which observation (summary of the sheet)

   observation	Dalton	Thomson	Rutherford	Bohr
   compounds form in whole-number ratios	yes	yes	yes	yes
   electrons come out of atoms	no	yes	yes	yes
   particles bounce back from foil	no	no	yes	yes
   hydrogen gives only a few colors	no	no	no	yes
   helium gives its own pattern of colors	no	no	no	no

10. 9.

    Tala reads the table. Which statement does it support?

    • Each model explained every row its predecessor did; none explains helium's colors
    • Bohr's model explains every row in the table, including the helium row
    • Thomson's model explains why alpha particles bounce back from the gold foil

11. Card

    Thomson's model (example numbers). Each atom bends an alpha particle by at most 0.01 degrees, in a random direction. Random bends add like the square root of their count. The foil is 1,000 atoms thick.

12. 10.

    Using the card, which argument shows Thomson's model cannot give a 90 degree turn, Zee?

    • Even with all 1,000 bends in line, the total is 10 degrees; random ones give 0.3
    • Random bends cancel completely, so the total would be exactly zero, not 90 degrees
    • 1,000 bends of 0.01 degrees easily add to 100 degrees, enough for a 90 degree turn