READING QUIZ

Which of these three kinds of rays carries no electrical charge?

1. gamma rays

2. alpha rays

3. beta rays

Atoms

Atom Size 10-10 meters

Nuclear Size 10 -15 meters

ChemistrySubstances are made of exact

ratios of the elements

Dalton’s Law of Definite Proportions

A simple cathode-ray tube consists of two electrodes sealed in a glass tube. A glow discharge appears in the

gas between the electrodes as the tube is evacuated. With further evacuation, the discharge disappears, and a glow

appears on the end of the tube opposite the cathode.

If the north pole of a magnet is brought down toward the top of a cathode-ray tube, the spot of light is deflected to the left across the face of the tube.

F=qvBElectron mass is 2000 times less than hydrogen mass (proton)_

Electron mass ~10-30 kg Electron charge -2x10 -19

Lecture Quiz Question 1

Choose the best answer:

A beam of electrons can be deflected by…

1. A constant electric field

2. Constant magnetic fields

3. Gravity

4. Variable electric or magnetic fields

5. All of the above.

Quiz 2

The size or scale of atoms is1. 10-6 meters

2. 10-9 meters

3. 10-10 meters

4. 10-12 meters

5. 10-15 meters

Lecture Quiz Question 3

How many grams of water can be produced by combining 16 grams of oxygen with 16 grams of hydrogen?

1. 0 grams

2. 16 grams

3. 18 grams

4. 24 grams

5. 32 grams

6. 36 grams

Thomson used both electric and magnetic fields to deflect the cathode-ray beam in a tube specially designed to

measure the mass of the cathode-ray particles.

How Does a TV work?

Roentgen noticed that a fluorescent material would glow when placed near his covered cathode-ray tube. The glow appeared only when the cathode-ray tube was turned on.

When Becquerel placed a piece of phosphorescent material on a covered photographic plate, the developed

plate showed a silhouette of the sample, indicating that the plate had been exposed by radiation

passing through the black paper cover.

Three forms of radiations:

alpha particles = 2p + 2n

beta particles = electrons

gamma rays = light (x-rays)

Early clues to composition of matter!

The contents of a Christmas present could be probed by firing a rifle into it and noting how

the bullets are scattered by the contents.

A beam of alpha particles was scattered from a thin gold foil in the experiments performed by Rutherford’s assistants.

Challenge Problem CP1

Lecture Quiz Question 4

Which is TRUE?

1. The nucleus of an atom takes up a lot more space than the electrons.

2. The nucleus has a lot more charge than the electrons.

3. The nucleus has a lot more mass than the electrons.

4. The nucleus always has more neutrons than protons.

5. The nucleus of a given element always has the same number of neutrons.

Summary of Chapter 18:

• Chemistry requires existence of atoms.

• Electrons, x-rays, alpha particles discovered (sub-atomic).

• Alpha rays establish nuclear model of atoms.

• Light emitted by atoms are in discrete wave lengths (lines).

• Spectrum of hot bodies requires light to be quantized, so light can act like a particle.

• Bohr model combines features to describe atom with quantized electron orbits, emitting light only during transitions.

• Particles can act like waves (electrons)!

• Quantum mechanics: electron wave functions describe atoms.

• Heisenberg Uncertainty Principle

Scanning Tunneling Microscope

Two atoms of hydrogen combine with one of oxygen to form water (H2O). The mass ratio is 8 to 1 because the

atomic mass of oxygen is 16 times the mass of hydrogen.

The periodic table can be formed by listing the elements in order of increasing atomic weight and

then cutting the list at certain points. Elements with similar chemical properties are then aligned in columns.