2.27 Predict trends in atomic radii and ionization energies based on placement in the periodic table.

What is the trend in atomic radii across a period based on an element’s position in the periodic table?

Trend Across a Period (Left to Right):

• Atomic radius decreases as you move from left to right across a period.

• Reason: As protons are added to the nucleus, the effective nuclear charge increases, pulling electrons closer to the nucleus. Even though electrons are added, they are added to the same energy level, so they don’t shield each other from the nuclear charge as much, reducing the size of the atom.

What is the trend in atomic radii down a group based on an element’s position in the periodic table?

Trend Down a Group (Top to Bottom):

• Atomic radius increases as you move down a group.

• Reason: As you go down a group, new electron shells are added, increasing the distance between the nucleus and the outermost electrons. This increases the size of the atom, even though the nuclear charge increases.

What is the trend in ionization energies across a period based on an element’s position in the periodic table?

Trend Across a Period (Left to Right):

• Ionization energy increases as you move from left to right across a period.

• Reason: As atomic radius decreases, the attraction between the nucleus and electrons becomes stronger, making it harder to remove an electron.

• Example: Elements on the right side (like noble gases) have higher ionization energies because their outer electrons are held tightly.

What is the trend in ionization energies down a group based on an element’s position in the periodic table?

• Trend Down a Group (Top to Bottom):

  • Ionization energy decreases as you move down a group.

  • Reason: As atomic radius increases, the outermost electrons are farther from the nucleus and are more shielded by inner electrons, making them easier to remove.