what is the trend in the atomic radii as the atomic number increases across a period? What is the exception to this trend?
I know the radius decreases as you go from left to right, but I can't figure the exception, I read somewhere that it's the noble gasses but I'm not sure.
The trend in atomic radii across a period (horizontal row) is that atomic radii generally decrease from left to right.
This trend can be explained by the increasing effective nuclear charge experienced by the electrons in the outer energy levels as you move across a period. The increasing number of protons in the nucleus pulls the outermost electrons closer, resulting in a smaller atomic radius.
However, there is an exception to this trend. The noble gases are the exception to this trend because they have relatively larger atomic radii compared to the elements in the same period. This is because the noble gases have completely filled electron shells, which results in electron-electron repulsion and the expansion of electron clouds, leading to larger atomic radii compared to the elements before them in the same period.
In summary, while atomic radii generally decrease across a period due to increasing effective nuclear charge, the noble gases have larger atomic radii compared to the elements in the same period due to completely filled electron shells.
The trend in atomic radii as the atomic number increases across a period is that the radius generally decreases from left to right. This can be explained by the increasing effective nuclear charge, which attracts the electrons more strongly, resulting in a smaller atomic radius.
The exception to this trend is indeed the noble gases. Noble gases are found in Group 18 of the periodic table and include elements such as helium, neon, and argon. They have a complete set of valence electrons, resulting in a stable electron configuration. As a result, noble gases have larger atomic radii compared to the elements preceding them in the same period.
To understand this exception, it's important to note that atomic radii are generally determined by the number of occupied electron shells and the effective nuclear charge. In general, as you move across a period from left to right, the effective nuclear charge increases, pulling the electrons closer to the nucleus and resulting in smaller atomic radii. However, when you reach the noble gases, they have completely filled electron shells, meaning they have a stable electron configuration. The electron-electron repulsion results in a slight increase in atomic radius compared to the elements before them.
So, to summarize, the trend in atomic radii across a period is a decreasing trend, but this trend is broken by the noble gases, which have larger atomic radii due to their stable electron configurations.