Ionization energy is the amount of energy required to remove one mole of electrons from one mole of atoms in the gaseous state. The ionization energy depends on several factors, including the nuclear charge, the distance of the electron from the nucleus, and the shielding effect of inner electrons. - Across a period (left to right): Ionization energy increases due to the increasing nuclear charge. As we move across a period, the atomic size decreases, and the electrons are pulled closer to the nucleus, making them harder to remove. This leads to higher ionization energy. - Down a group (top to bottom): Ionization energy decreases because of the increasing atomic size and the shielding effect. Electrons in the outermost shell are farther from the nucleus and experience more repulsion from inner electrons, making them easier to remove. Now, let's analyze the elements: - Lithium (Li) has an atomic number of 3 and is in Group 1, Period 2. It has a low first ionization energy because it only has one electron in its outermost shell, which is far from the nucleus and easily removed.
- Sodium (Na), in Group 1, Period 3, has a lower ionization energy than lithium because its outer electron is farther from the nucleus.
- Neon (Ne), in Group 18, Period 2, is a noble gas with a stable electron configuration. It has the highest first ionization energy because its electrons are tightly bound to the nucleus and it has a complete octet configuration.
- Magnesium (Mg), in Group 2, Period 3, has a higher ionization energy than sodium but lower than neon, as it is in the same period as sodium but has an extra proton in the nucleus. Therefore, Neon (Ne) has the highest first ionization energy.