Which one of the following has the smallest radius? a) Na b) Cl c) Fe d) P e) Br
The correct answer and explanation is:
Smallest Radius:
Answer: c) Fe
Explanation:
The atomic radius of an element is the distance from the nucleus to the outermost electron. Atomic radii tend to decrease across a period (from left to right) due to the increased effective nuclear charge. This higher charge pulls the electrons closer to the nucleus, reducing the size of the atom. Conversely, atomic radii increase down a group because the addition of electron shells places the outermost electrons farther from the nucleus, decreasing the pull of the nucleus on these electrons.
- Na (Sodium) is in Group 1 and Period 3. Being an alkali metal, it has a relatively large radius due to fewer protons and an electron configuration with a single electron in its outer shell.
- Cl (Chlorine) is in Group 17 and Period 3. It has more protons than Na, so the atomic radius is smaller because of the increased nuclear charge.
- Fe (Iron) is in Group 8 and Period 4. Fe has a higher nuclear charge (26 protons) compared to Na and Cl, but it’s in a period further to the right. The increased number of protons pulls the electrons closer to the nucleus, giving it a smaller atomic radius than the others.
- P (Phosphorus) is in Group 15 and Period 3, which makes its radius smaller than Na but larger than Fe.
- Br (Bromine) is in Group 17 and Period 4. It’s in the same period as Fe, but the number of protons is lower, giving it a slightly larger radius than Fe.
Thus, Fe has the smallest radius because it has a higher nuclear charge and is located further along the periodic table.