Chapter 2 Section 9: Checking Up

Which of the following explains the difference between atomic mass and atomic number?

• Atomic mass is the number of protons in the nucleus, while atomic number includes the mass of protons, neutrons, and electrons.
• Atomic mass is the total number of particles in an atom, while atomic number is the total mass of an atom.
• Atomic mass includes the mass of protons, neutrons, and electrons, while atomic number is the number of protons in the nucleus.
• Atomic mass is the number of electrons in an atom, while atomic number is the total mass of the nucleus.

What two forces are at work in the nucleus of an atom?

• Strong nuclear force and electromagnetic force
• Weak nuclear force and gravitational force
• Electrostatic force and gravitational force

• Strong nuclear force and electrostatic coulomb force

What is electrostatic coulomb force?

• Force between two charged objects is inversely proportional to the charges
• Force between two charged objects is directly proportional to the size

• Force between two charged objects is constant regardless of the charges
• A repulsion force and is strong at close range but becomes weaker as the distance between the protons becomes greater.

What is strong, nuclear force?

• The strong nuclear force is the force that repels atomic nuclei.
• The strong, nuclear force is very strong at close distances but becomes insignificant as the particles become farther apart.

• The strong nuclear force is the force that causes objects to fall to the ground.
• The strong nuclear force is responsible for the attraction between electrons and protons.

What is an isotope?

• Molecules with the same atomic number.
• Atoms of different elements with different numbers of protons.
• Atoms of the same element with different numbers of neutrons.
• Different elements with the same number of neutrons.

Why are some isotopes unstable?

• Isotopes are unstable due to having an equal number of protons and neutrons.
• Isotopes are unstable due to an imbalance of protons and neutrons in their nuclei.
• Isotopes are unstable because they are always found in a gaseous state.
• Isotopes are unstable due to their inability to form chemical bonds.

What percentage of a radioactive sample remains after three half-lives?

• 25%
• 50%
• 12.5%
• 75%

Suppose you have 500 g of a radioactive sample with a half-life of 100 years.

How much of the sample would be radioactive after 400 years?

• 62.5 g
• 250 g
• 125 g
• 31.25 g