Three atoms have the following electron configurations: (a) 1s2 2s2 2p6 3s2 3p3 (b) 1s2 2s2 2p6 3s2 3p6 (c) 1s2 2s2 2p6 3s2 3p6 4s2 Which of the three has the largest Ei2? Which has the smallest Ei7?

Ionization energy is the energy required to remove an electron from an atom or ion in its gaseous state. It is a critical concept in understanding how easily an atom can lose electrons, which is influenced by factors such as atomic size, nuclear charge, and electron shielding. Generally, ionization energy increases across a period and decreases down a group in the periodic table.

Electron configuration describes the distribution of electrons in an atom's orbitals. It provides insight into the atom's chemical properties and reactivity. The configurations given in the question indicate the number of electrons in each energy level and sublevel, which directly affects the atom's ionization energies and how tightly electrons are held by the nucleus.

Trends in ionization energy refer to the predictable changes in ionization energy values across periods and groups in the periodic table. As you move from left to right across a period, ionization energy generally increases due to increased nuclear charge and decreased atomic radius. Conversely, as you move down a group, ionization energy decreases because of increased electron shielding and greater distance from the nucleus, making it easier to remove electrons.