Order the elements S, Cl, and F in terms of increasing atomic radii.
I thought the answer was F, S, Cl, but the answer key said it was S, F, CL
Why? AR decreases from left to right. Sulfur has one more energy level, so shouldn't its atomic radii be greater than fluorine?
I think it is F smallest to Cl to S the largest which doesn't agree with your answer key. See the link below and look under calculated value. http://en.wikipedia.org/wiki/Atomic_radii_of_the_elements_(data_page)
Yes, AR decreases from left to right, which is why I think S is larger than Cl BUT F is not in the same period. AR ALSO decreases as we move UP in a column. Using your rationale, He should be larger than F (but it is smaller).
To determine the correct order of the elements in terms of increasing atomic radii, we need to consider a few factors.
First, you are correct that atomic radii generally decrease from left to right across the periodic table, as the effective nuclear charge increases, pulling the outermost electrons closer to the nucleus. So based on this trend, we would expect chlorine (Cl) to have a smaller atomic radius than both sulfur (S) and fluorine (F).
Next, we need to consider the impact of the number of occupied energy levels on atomic radii. Generally, within a period (or row) of the periodic table, the number of occupied energy levels increases from left to right. However, when comparing elements from different periods, you cannot solely rely on this factor to determine atomic radii.
In the specific case of sulfur, fluorine, and chlorine, sulfur is indeed located in a lower period than both fluorine and chlorine, meaning it has one more occupied energy level. Normally, this would mean that sulfur has a larger atomic radius than both fluorine and chlorine.
However, there is another factor we need to consider: the concept of effective nuclear charge. Along a period, the increase in nuclear charge (protons in the nucleus) pulls the electrons closer, decreasing atomic radii. In the case of sulfur, even though it has an additional energy level, the increase in effective nuclear charge due to the additional protons in its nucleus compensates for the extra energy level. As a result, sulfur ends up having a smaller atomic radius compared to chlorine.
So, based on both trends of atomic radii - the increase in effective nuclear charge along a period and the increase in the number of occupied energy levels down a group - the correct order of the elements in terms of increasing atomic radii is S, F, Cl.
You are correct that generally, atomic radii decrease as you move from left to right across a period on the periodic table. However, when comparing elements in the same period, the number of energy levels does not always determine the atomic radii.
In this case, Sulfur (S) and Chlorine (Cl) are in the same period (period 3), so we compare their atomic radii. Chlorine, being on the right side of the period, has a smaller atomic radius than Sulfur, which is on the left side. Therefore, Sulfur (S) has a larger atomic radius than Chlorine (Cl).
Fluorine (F) is in the period below (period 2) and has a smaller atomic radius than both Sulfur and Chlorine. This is because as you move down a group, the number of energy levels increases, leading to larger atomic radii. Therefore, the correct order of elements in terms of increasing atomic radii is Sulfur (S), Fluorine (F), and Chlorine (Cl).