Three atoms have the following electron configurations: (a) 1s2 2s2 2p6 3s2 3p1 (b) 1s2 2s2 2p6 3s2 3p5 (c) 1s2 2s2 2p6 3s2 3p6 4s1. Which of the three has the largest Ei1? Which has the smallest Ei4?

Ionization energy (Ei) is the energy required to remove an electron from an atom in its gaseous state. The first ionization energy (Ei1) refers to the energy needed to remove the outermost electron, while the fourth ionization energy (Ei4) involves removing the fourth electron. Generally, ionization energy increases across a period due to increased nuclear charge and decreases down a group due to increased distance from the nucleus and electron shielding.

Electron configuration describes the distribution of electrons in an atom's orbitals. It provides insight into an 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 influences the atom's ionization energies. Understanding these configurations helps predict which atom will have higher or lower ionization energies based on their electron arrangements.

Ionization energy exhibits specific trends in the periodic table: it generally increases from left to right across a period and decreases from top to bottom within a group. This trend is due to factors such as effective nuclear charge and electron shielding. Atoms with more protons in the nucleus (higher atomic number) tend to have higher ionization energies, as they hold their electrons more tightly, making it harder to remove them.