The existence of isotopes violates one of the original ideas of Dalton’s atomic theory. Which one?
← Back to Chemistry 2e
Chemistry 2e · 2.2 Evolution of Atomic Theory
Evolution of Atomic Theory: practice problems
3 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.
Exercises 7
How are protons and neutrons similar? How are they different?
Exercises 9
Predict and test the behavior of α particles fired at a Rutherford atom model.
(a) Predict the paths taken by α particles that are fired at atoms with a Rutherford atom model structure. Explain why you expect the α particles to take these paths.
(b) If α particles of higher energy than those in (a) are fired at Rutherford atoms, predict how their paths will differ from the lower-energy α particle paths. Explain your reasoning.
(c) Predict how the paths taken by the α particles will differ if they are fired at Rutherford atoms of elements other than gold. What factor do you expect to cause this difference in paths, and why?
(d) Now test your predictions from (a), (b), and (c). Open the Rutherford Scattering simulation and select the “Rutherford Atom” tab. Due to the scale of the simulation, it is best to start with a small nucleus, so select “20” for both protons and neutrons, “min” for energy, show traces, and then start firing α particles. Does this match your prediction from (a)? If not, explain why the actual path would be that shown in the simulation. Pause or reset, set energy to “max,” and start firing α particles. Does this match your prediction from (b)? If not, explain the effect of increased energy on the actual path as shown in the simulation. Pause or reset, select “40” for both protons and neutrons, “min” for energy, show traces, and fire away. Does this match your prediction from (c)? If not, explain why the actual path would be that shown in the simulation. Repeat this with larger numbers of protons and neutrons. What generalization can you make regarding the type of atom and effect on the path of α particles? Be clear and specific.
Key terms · 6
- alpha particle (α particle)
- positively charged particle consisting of two protons and two neutrons
- electron
- negatively charged, subatomic particle of relatively low mass located outside the nucleus
- isotopes
- atoms that contain the same number of protons but different numbers of neutrons
- neutron
- uncharged, subatomic particle located in the nucleus
- nucleus
- massive, positively charged center of an atom made up of protons and neutrons
- proton
- positively charged, subatomic particle located in the nucleus
Learn 2.2 on the whiteboard
The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.