Atomic Structure and Theory Review

Name: ______Date: ______Period: ______Page: ______

+Put the number of the definition from the list below into the square with the appropriate term. Not all definitions will be used. Check your answers by adding the numbers to see if all the sums of all rows, both across and down add up to the same number, the Magic #.

Democritus Dalton Thomson Chadwick Total

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Rutherford Proton Atom Bohr

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Wave Model Neutron Nucleus Alpha particle

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Electron Model Energy levels Electron cloud

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Total ______

Magic Number ______1. Represented by a symbol; all are found on the Periodic Table 2. Greek philosopher that made a mental model of the atom 3. Used by Rutherford in his experiment; made of two protons and two neutrons 4. The fixed paths in which electrons circle the nucleus according to the Bohr model 5. The positive particle in the nucleus of an atom 6. The tiny positive core of an atom; contains protons and neutrons 7. English schoolteacher that formed the atomic theory model of the atom 8. Discovered the nucleus using his gold foil experiment 9. Current explanation of the probable location of electrons in the atom 10. Used by scientists to explain something we cannot see or understand 11. The smallest particle of an element that has the properties of that element 12. Discovered the neutron 13. Current model of the atom proposed by Schrodinger (electrons behave more like this than particles) 14. Mass of protons and neutrons 15. Developed the model of the atom in which electrons orbit the nucleus in energy levels 16. The negative particle that circles the nucleus 17. The neutral particle in the nucleus of an atom 18. Proposed the “plum-pudding” model of the atom and discovered the electron Ernest Rutherford’s Contributions to Atomic Theory

Ernest Rutherford (1871-1937) was digging potatoes in a field in his native country of New Zealand when he received a letter from J. J. Thomson, informing him that he had been accepted as Thomson’s student at Cambridge University. Rutherford was honored to be selected to join this prestigious group of scientists but was unaware that he would be making giant steps towards unraveling the secrets of the atom.

As Thomson’s pupil, Rutherford wanted to investigate atomic structure. He determined that the best way to learn about the inside of the atom was to blow it apart. Rutherford chose the nucleus of the helium atom as the “bullet” to shoot at the atom. The helium nucleus (an alpha particle) contains two protons and two neutrons. The “gun” to fire the alpha particle was the element radium. Radium is radioactive, continually emitting alpha particles as products of its radioactive decay process. He placed the radium in a heavy lead container with just a small opening to direct the escaping alpha particles. The target for the alpha particles was a very thin sheet of gold foil, less than 1/100,000 of an inch thick. (This is even thinner than the aluminum foil used to cover food.) Yet, because atoms are so small, the gold foil still had a thickness of more than 2,000 atoms.

For his first series of experiments, Rutherford set the foil in front of the radium container. Behind the foil, he placed a screen which would fluoresce whenever it was struck by an alpha particle. Thus, he could observe whether any alpha particles were able to pass through the atoms in the gold foil. The actual results were unexpected. Rutherford saw many flashes of light from the screen. Somehow the alpha particles were able to get through the “solid” gold foil. When Rutherford moved the screen to the sides and to the front, facing the foil, to his amazement, the screen fluoresced at many different angles. Some of the particles bounced off at angles to the side as well as straight back at the radium. Rutherford has been often quoted as saying, “It was as if you fired a mortar at a piece of tissue paper and it bounced right back at you.”

In 1911, Rutherford explained what had happened by suggesting that the atom consisted of a very small, heavy central core called the nucleus, and very far away from the nucleus were the rapidly swirling electrons. The atom was largely empty space, which explained how the alpha particles were able to get through the gold foil. The small, heavy nucleus with a positive charge caused the deflection of some of the positive alpha particles. A small number of alpha particles actually hit the nucleus of the gold atoms and were deflected directly back toward the source.

Rutherford performed another group of experiments similar to the first using nitrogen as the target to confirm his model of the atom. Most of the alpha particles went straight through the empty space of the nitrogen atoms; however, a few bumped into the nucleus and bounced off. In addition, he discovered the presence of positively charged hydrogen nuclei. This led him to hypothesize that the hydrogen nuclei had to come from within the nitrogen atoms. Rutherford later concluded that the atoms of every element contain one or more of these positively charged nuclei. These positive hydrogen nuclei are called protons. On the basis of these results, he revised the existing model of the atom. Rutherford proposed that the atom is mostly empty space with a heavy, positively charged nucleus and negatively charged outlying electrons.

Particle Mass (g) Charge (c) Electric charge Proton 1.673 x 10-24 1.602 x 10-19 +1 Neutron 1.675 x 10-24 0 0 Electron 9.109 x 10-28 -1.602 x 10-19 -1 Read the article “Ernest Rutherford’s Contributions to Atomic Theory” and respond to the following questions.

1. An alpha particle is

a. the first particle.

b. the helium nucleus.

c. a bullet.

d. the element radium.

2. Deflected (line______) means

a. bounced.

b. explained.

c. swirled.

d. transmitted.

3. Most of the alpha particles were able to get through the gold foil because the

a. gold foil was very thin.

b. alpha particles are powerful forms of radiation.

c. nucleus of the atom is positively charged.

d. atom is largely empty space.

4. Rutherford’s work demonstrates that

a. science is an ongoing endeavor that changes as new information modifies existing theory.

b. scientific theory, once developed, is the law and can be applied in all science disciplines.

c. when experimental data is not consistent with the hypothesis, a scientist creatively relates the two.

d. it is often difficult for one scientist to reproduce another scientist’s experimental results.

5. Which of the following statements is NOT consistent with the results obtained in Rutherford’s gold foil experiment? a. The nucleus of an atom is positively charged.

b. The nucleus of an atom contains almost all the mass of the atom.

c. Atoms are composed mainly of empty space.

d. Electrons are contained in the nucleus of an atom.

6. Considering that opposites attract, why did the electrons not attract the alpha particles and cause them to stop?

7. List at least two characteristics of the nucleus.