(a) What is the trend in first ionization energies as one proceeds down the group 17 elements? Explain how this trend relates to the variation in atomic radii. (b) What is the trend in first ionization energies as one moves across the fourth period from K to Kr? How does this trend compare with the trend in atomic radii?

Ionization energy is the energy required to remove an electron from a gaseous atom or ion. It generally increases across a period due to increasing nuclear charge, which attracts electrons more strongly. Conversely, it decreases down a group because the outer electrons are farther from the nucleus and experience greater shielding from inner electrons, making them easier to remove.

Atomic radius refers to the size of an atom, typically measured from the nucleus to the outermost electron shell. As one moves down a group, atomic radii increase due to the addition of electron shells. In contrast, moving across a period, atomic radii decrease because increased nuclear charge pulls the electron cloud closer to the nucleus, reducing the size of the atom.

Trends in the periodic table, such as those for ionization energy and atomic radius, reflect the underlying principles of atomic structure and electron interactions. As you move down a group, ionization energy decreases and atomic radius increases, while moving across a period shows the opposite trend. Understanding these trends helps predict the behavior of elements in chemical reactions and bonding.