Atomic Theory

Why has the atomic theory changed over time?

• Theories always change over time.

• The feelings of scientists changed over time.

• Other scientists interpreted Democritus' evidence differently.

• After new, relevant evidence emerged, scientists reevaluated the theory.

Ben wants to model how the motion of particles changes with temperature. He considers

water in an iron pot. Ben draws a model to show how the water particles and iron particles

move at room temperature. Then, he draws a second model to show how the water

particles and iron particles move as the pot of water is heated. How should Ben's second

model differ from the first?

• The water particles should vibrate faster, and the iron particles should not move

• Both the water particles and the iron particles should slide past each other faster

• The water particles should slide past each other faster, and the iron particles should vibrate faster

• The water particles should move freely in all directions, and the iron particles should slide past each other faster

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Chuck wants to investigate how gas molecules move in a container. Which model would

be most helpful to represent this motion?

• Stacking blocks to build a tower

• Freezing water in an ice cube tray

• Bouncing elastic balls off of each other and the walls of a room

• Rolling ping pong balls around in a closed bag

Why does a gas take the shape of its container, while solids of the same substance do not?

• The mass of the particles in the gas is less than the mass of the particles in the solid.

• The particles in the gas are farther apart and move faster than the particles in the solid.

• The particles in the gas are smaller and move more slowly than the particles in the solid.

• The space between particles in the gas is smaller than the space between particles in the solid.

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Which model (or models) above could be Tyson's drawing of particles in a solid?

• Model 1

• Model 3

• Model 2 and Model 3

• Model 1, Model 2, and Model 3

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How does the behavior of particles in a solid prevent it from flowing from place to place?

• The particles are unable to vibrate.

• The particles are unable to form a regular pattern.

• The particles are closely packed and have little empty space between them.

• The particles experience weak intermolecular forces which repel each other.

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Based on the provided Periodic Table of Elements, which of the following sets of elements have similar properties?

• Pb-82, Sn-50, Kr-36

• Ne-10, N-7, O-8

• Cl-17, Br-35, 1-53

• O-8, S-16, N-7

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Atoms and molecules combine to form all the matter we see in our universe. They have

unique identities that characterize them and separate them from one another. Atoms can

bond together to make larger samples of matter, such as compounds. Atoms are also

found in mixtures. Which statement correctly contrasts a compound and a mixture?

• A compound is made of a fix ratio of two or more elements chemically combined, and a mixture can contain two or more compounds physically combined.

• A compound contains two or more elements that are physically combined, and a mixture contains two or more compounds that are chemically combined.

• A mixture combines to form a compound that cannot be separated physically, and a compound displays physical characteristics of the mixture.

• A compound and mixture differ in the number of elements they contain, and both cannot be separated physically or chemically.

Which of the following describes how elements are arranged in the periodic table?

• by decreasing atomic mass

• by increasing atomic number

• by chemical name

• by repeating atomic number

The diagram below shows a model of an atom. Which label points to the electrons?

• A

• B

• C

• D

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