Use the concepts of effective nuclear charge, shielding, and n value of the valence orbital to explain the trend in atomic radius as you move across a period in the periodic table.
This is a thinking question. We shall be happy to critique your thoughts.
To explain the trend in atomic radius as you move across a period in the periodic table using the concepts of effective nuclear charge, shielding, and the n value of the valence orbital, we need to understand each of these concepts:
1. Effective Nuclear Charge: The effective nuclear charge is the net positive charge experienced by the valence electrons in an atom. It is determined by subtracting the number of inner electrons or shielding electrons from the total number of protons in the nucleus. The greater the effective nuclear charge, the stronger the attraction between the electrons and the nucleus.
2. Shielding: Shielding, in this context, refers to the blocking or screening effect of inner electrons on the valence electrons. Inner electrons repel valence electrons, reducing or shielding the attractive force between the valence electrons and the nucleus. The more inner electrons there are, the greater the shielding effect.
3. Valence Orbital (n value): The n value represents the principal quantum number, which indicates the energy level or shell in which the valence electrons are located. Each energy level can accommodate different numbers of electrons, and electrons in higher energy levels are farther from the nucleus compared to those in lower energy levels.
Now, let's apply these concepts to explain the trend in atomic radius across a period in the periodic table:
As you move across a period from left to right, the atomic radius generally decreases. This trend can be explained as follows:
1. Effective Nuclear Charge: Moving across a period, the number of protons in the nucleus increases, resulting in a higher effective nuclear charge. The increased positive charge in the nucleus attracts the electrons more strongly, pulling them closer to the nucleus.
2. Shielding: Although the number of protons increases, the number of shielding or inner electrons often remains the same across a period. Since the shielding effect does not significantly increase, the increased effective nuclear charge dominates, resulting in a stronger attraction between the valence electrons and the nucleus.
3. Valence Orbital (n value): In a period, the n value for the valence orbital remains the same since all elements within a period have valence electrons in the same energy level. Therefore, the influence of the valence orbital on the atomic radius remains constant.
Overall, due to the combination of an increasing effective nuclear charge and relatively constant shielding, the valence electrons are pulled closer to the nucleus, leading to a smaller atomic radius as you move across a period from left to right in the periodic table.