Unit 2: Atoms and Elements

How did arranging elements by comparing atomic mass with other chemical and physical properties allow Mendeleev to predict the reactivity of undiscovered elements?

• Mendeleev noticed gaps in the pattern of reactivity he observed.

• Mendeleev noticed that as atomic mass increased, reactivity decreased.

• Mendeleev noticed gaps in atomic mass, which represented reactive elements.

• Mendeleev noticed that nonmetals and metals follow different patterns of reactivity.

Which of these must happen for a large nucleus to remain stable?

• The weak nuclear force must overcome the electrostatic force.

• The electrostatic force must overcome the strong nuclear force.

• The strong nuclear force must overcome the electrostatic force.

• The gravitational force must overcome the strong nuclear force.

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Which atom would require the most energy to break its nucleons apart?

• a silicon atom with a mass of 28 amu

• a calcium atom with a mass of 40 amu

• a vanadium atom with a mass of 51 amu

• a potassium atom with a mass of 39 amu

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Which statement explains the trend in atomic radius on the periodic table?

• It generally increases from left to right because the greater number of electrons increases their distance from the nucleus.

• It generally decreases from left to right because the increase in charge within the nucleus pulls electrons closer.

• It generally increases from top to bottom because the attraction from the nucleus has to pull on fewer electrons.

• It generally decreases from top to bottom because more electrons in the same shell increases the pull of the nucleus on them.

Which answer describes how different forces act on protons in the nucleus?

• Electrostatic force causes protons to repel one another until they are more than a few proton diameters apart, where the gravitational force becomes greater than the electrostatic force.

• The strong nuclear force causes protons to attract one another until they are more than a few proton diameters apart, where the electrostatic force becomes greater than the strong nuclear force.

• Electrostatic and gravitational forces cause protons to attract one another until they are more than a few proton diameters apart, where the strong nuclear force becomes stronger than the other forces.

• Electrostatic force causes protons to attract one another until they are more than a few proton diameters apart, where the electrostatic force reverses direction and causes the protons to repel each other.

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In the gold foil experiment, positive particles were directed at gold atoms to find out about the interior of an atom.

Which direction recorded the most particles to support the claim that an atom is mostly empty space?

• Direction A

• Direction B

• Direction C

• Direction D

Number of protons in an atom

• mass number

• atomic number

• average atomic mass

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Weighted average mass of all naturally occurring isotopes of an element

• mass number

• atomic number

• average atomic mass

Alpha Emissions =

• produce an electron or positron

• high energy form of radiation

• loses 2 protons and 2 neutrons

• most hazardous emission

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Beta Emissions =

• produces an electron or a positron

• high energy radiation

• most hazardous radiation

• produces 2 protons and 2 neutrons

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