Sodium (Na) and aluminum (Al) are both metallic elements, but they have some differences in terms of atomic radius, ionization energy, and electron affinity.
Atomic Radius: The atomic radius refers to the size of the atom. In general, the atomic radius tends to decrease as you move from left to right across a period in the periodic table. Sodium is located in Group 1 (the alkali metals) and aluminum is in Group 13 (the boron group). As you move down a group, the atomic radius tends to increase due to the addition of new electron shells. Therefore, aluminum has a larger atomic radius compared to sodium.
Ionization Energy: Ionization energy is the energy required to remove an electron from an atom or ion. Sodium has a lower ionization energy than aluminum. This is because sodium has a single valence electron in its outermost shell (2s1), which is relatively far from the positively charged nucleus. Therefore, it is easier to remove this electron from sodium compared to aluminum, which has three valence electrons in its outermost shell (3s2 3p1). The presence of additional electrons and a stronger attraction from the nucleus in aluminum increases the ionization energy.
Electron Affinity: Electron affinity is the energy change that occurs when an atom gains an electron to form a negative ion (anion). Both sodium and aluminum have positive electron affinities, indicating that they release energy when they gain an electron. However, the electron affinity of aluminum is generally higher than that of sodium. Aluminum has a stronger attraction for an additional electron due to its higher nuclear charge and smaller atomic radius, resulting in a greater electron affinity.
The differences in these properties between sodium and aluminum can be attributed to their respective positions in the periodic table and the atomic structure of their atoms. As elements, sodium and aluminum have different numbers of electrons, electron configurations, and effective nuclear charges, which influence their atomic and chemical behaviors.