The lightest atom is the hydrogen atom. There is one proton in its nucleus. a) what is the mass of the hydrogen atom ?
b) how many electrons in an atom ?
(Answer the a and b questions)

Hydrogen is the smallest chemical element because it consists of only one proton in its nucleus. Its symbol is H, and its atomic number is 1 .It has an average atomic weight of 1.0079 amu, making it the lightest element.

a.1.00784 u

b.Atomic-36

Kr

Krypton

Atomic Weight. 83.80

That means that there must be a balance between the positively charged protons and the negatively charged electrons. Atoms must have equal numbers of protons and electrons. In our example, an atom of krypton must contain 36 electrons since it contains 36 protons. Electrons are arranged around atoms in a special way.