Unit5: Periodic Trends

What is the atomic radius?

• a) The amount of energy required to remove an electron from an atom.

• b) The distance from the nucleus to the outermost shell of electrons.

• c) The tendency of an atom to attract electrons.

• d) None of the above.

Answer explanation

The atomic radius is defined as the distance from the nucleus to the outermost shell of electrons, making option b) the correct choice. The other options describe different atomic properties.

In which units is the atomic radius typically measured?

• a) Nanometers (nm)

• b) Meters (m)

• c) Picometers (pm) or angstroms (Å)

• c) Picometers (pm) or angstroms (Å)

Answer explanation

The atomic radius is typically measured in picometers (pm) or angstroms (Å) because these units are suitable for the small scale of atomic dimensions, making option c) the correct choice.

How does the atomic radius change across a period from left to right?

• a) Increases

• b) Decreases

• c) Stays the same

• d) Increases, then decreases

Answer explanation

The atomic radius decreases across a period from left to right due to increasing nuclear charge, which pulls electrons closer to the nucleus, resulting in a smaller atomic size.

How does the atomic radius change down a group?

• a) Decreases

• b) Increases

• c) Stays the same

• d) Increases, then decreases

Answer explanation

The atomic radius increases down a group due to the addition of electron shells, which outweighs the increase in nuclear charge, resulting in larger atomic size.

What is the first ionization energy?

• a) The energy required to add an electron to a neutral atom.

• b) The energy required to remove the outermost electron from a neutral atom.

• c) The tendency of an atom to attract electrons.

• d) The distance from the nucleus to the outermost shell of electrons.

Answer explanation

The first ionization energy is defined as the energy required to remove the outermost electron from a neutral atom, making option b the correct choice. This process is crucial in understanding atomic behavior.

How does the first ionization energy generally change across a period?

• a) Increases

• b) Decreases

• c) Stays the same

• d) Decreases, then increases

Answer explanation

The first ionization energy generally increases across a period due to increasing nuclear charge, which attracts electrons more strongly, making them harder to remove. Thus, the correct answer is a) Increases.

How does the first ionization energy change down a group?

• a) Increases

• b) Decreases

• c) Stays the same

• d) Increases, then decreases

Answer explanation

The first ionization energy decreases down a group due to increased atomic size and shielding effect, making it easier to remove the outermost electron. Thus, the correct answer is b) Decreases.

What is electronegativity?

• a) The energy required to add an electron to a neutral atom.

• b) The distance from the nucleus to the outermost shell of electrons.

• c) The tendency of an atom to attract and hold onto electrons in a chemical bond.

• d) The energy required to remove an electron from an atom.

Answer explanation

Electronegativity is defined as the tendency of an atom to attract and hold onto electrons in a chemical bond, making option c the correct choice. The other options describe different concepts related to atomic structure.

How does electronegativity change across a period?

• a) Increases

• b) Decreases

• c) Stays the same

• d) Decreases, then increases

Answer explanation

Electronegativity increases across a period due to the increasing nuclear charge, which attracts electrons more strongly. This trend is observed as you move from left to right in the periodic table.

How does electronegativity change down a group?

• a) Increases

• b) Decreases

• c) Stays the same

• d) Increases, then decreases

Answer explanation

Electronegativity decreases down a group due to increased atomic size and shielding effect, which reduces the nucleus's ability to attract bonding electrons. Thus, the correct answer is b) Decreases.