Why is a hydrogen bond a relatively weak bond?

Hydrogen bonds are intermolecular (“between-molecule”) bonds, rather than intramolecular (“within-molecule”) bonds. They occur not only in water but in other polar molecules in which positive hydrogen atoms are attracted to negative atoms in nearby molecules. Hydrogen bonds are relatively weaker as chemical bonds. For example, they are much weaker than the bonds holding atoms together within molecules of covalent compounds.

Hydrogen bond is weaker than ionic and covalent bonds. Example: Water molecules are held to each other by intermolecular forces of attraction. Covalent bonds are the strongest bonds, meaning that atoms are actually held together by the physical sharing of electrons.

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.