Which element has the smallest covalent radius on the periodic table?

• A. Helium (He)
• B. Fluorine (F)
• C. Hydrogen (H)
• D. Neon (Ne)

Answer: (A)

Verified step by step guidance

1. Understand that the covalent radius of an element refers to the size of its atoms when they are covalently bonded to another atom.
2. Recall that atomic size generally decreases across a period (left to right) on the periodic table due to increasing effective nuclear charge pulling electrons closer to the nucleus.
3. Identify the elements given: Helium (He), Fluorine (F), Hydrogen (H), and Neon (Ne), and note their positions on the periodic table. Helium and Neon are noble gases in period 1 and 2 respectively, Fluorine is a halogen in period 2, and Hydrogen is in period 1.
4. Recognize that noble gases typically have smaller atomic radii compared to other elements in the same period because of their full electron shells, but covalent radius data for noble gases can be less straightforward since they rarely form covalent bonds.
5. Compare the covalent radii trends and conclude that Helium, being in the first period with only one electron shell and a high effective nuclear charge, has the smallest covalent radius among the options.