Development of atomic modelsIB MYP Sciences: Subtopic test

1. 1
   A science museum in Auckland is building a wall display that shows how scientists' ideas about the atom changed between 1803 and 1913. Each panel names a scientist, the date and the model of the atom that they proposed.

   (a)

   The first panel is about John Dalton in 1803. How did Dalton picture an atom?

   [1 mark]

   • AA tiny solid sphere that cannot be divided
   • BA positive sphere with electrons embedded in it
   • CA tiny nucleus surrounded by orbiting electrons
   • DA nucleus with electrons in fixed shells

   (b)

   The last panel is about Niels Bohr in 1913. Which statement describes the Bohr model of the atom?

   [1 mark]

   • AAtoms are solid spheres of the same material throughout
   • BNegative electrons are scattered through a positive sphere
   • CElectrons orbit the nucleus in fixed shells at set distances
   • DElectrons orbit a small nucleus in a mixture of different paths

   (c)

   Describe the plum pudding model of the atom proposed by J. J. Thomson after he discovered the electron in 1897.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In 1909, Hans Geiger and Ernest Marsden, working in Ernest Rutherford's laboratory in Manchester, fired a beam of alpha particles (small, positively charged particles) at a very thin sheet of gold foil. Most of the alpha particles passed straight through the foil. A small number were deflected through large angles, and about one in 8000 bounced almost straight back towards the source.

   (a)

   Most of the alpha particles passed straight through the gold foil. What does this show about atoms?

   [1 mark]

   • AAtoms are solid spheres
   • BThe nucleus takes up most of the atom
   • CElectrons are heavier than alpha particles
   • DMost of an atom is empty space

   (b)

   A few alpha particles were deflected through large angles. What is the best explanation?

   [1 mark]

   • AThey were attracted to the negative electrons
   • BThey were repelled by a small, dense, positively charged nucleus
   • CThey were spread out by positive charge across the whole atom
   • DThey passed through the atom without meeting anything

   (c)

   Explain why the results of this experiment could not be explained by the plum pudding model.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A class in Singapore models the gold foil experiment. A small, hard, cone-shaped object is hidden under a flat cloth on a table. Students roll 50 identical marbles at the cloth from the same starting line, aiming along parallel lines spaced evenly across the cloth, and record the direction in which each marble leaves the cloth. Results: 41 marbles roll straight across, 7 are deflected slightly and 2 bounce back.

   (a)

   Identify the independent variable, the dependent variable and one control variable in the students' investigation.

   [3 marks]

   (b)

   Evaluate how well the students' model represents Rutherford's experiment.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   In 1913 the Danish physicist Niels Bohr proposed that electrons orbit the nucleus in fixed shells. His model explained why a heated element gives out light of only certain colours, which Rutherford's model could not explain. Later work showed that Bohr's model is also incomplete, and more detailed models are now used. A science teacher in Cairo tells her class: "Scientific models keep changing, so we cannot trust science."

   (a)

   Describe how the model of the atom changed from Dalton to Bohr, and the evidence that led to each change.

   [6 marks]

   (b)

   Evaluate the teacher's statement that "Scientific models keep changing, so we cannot trust science."

   [6 marks]

   Total for question 4: 12 marks

End of questions