Question

hi...guys

while moving from left to right in a period the atomic size decreases then why the hydrohen has smaller size than helium though it is to the left of helium​

Answer 1

Helium (He) has the highest ionization energy because, like other noble gases, helium's valence shell is full. Therefore, helium is stable and does not readily lose or gain electrons. Explanation: Atomic radius increases from right to left on the periodic table. Therefore, nitrogen is larger than oxygen.

Answer 2

Along a period (left to right) the atomic number increases while the valence electrons remain in the same shell. Thus due to the increasing nuclear charge (protons) which attracts electrons closer to the nucleus makes the radii of the atoms decrease left to right. Hydrogen and Helium are in the same period.