<span>When a chemist mixes oxygen gas and hydrogen gas to form
water, which is composed of one oxygen and two hydrogen atoms per molecule. The hydrogen and oxygen atoms bounds together by making a bond called covalent bond.<span> In a covalent bond, two atoms are bound
together because they each want to "share" each other's electrons.</span></span>
Fluorine has 9 protons and 9 electrons
Iodine has 53 protons and 53 electrons
I thinking the limitation is that a shifting electron will always move from a more excited states to a less excited state. Electrons could not circle the nucleus because they would lose energy by emitting electromagnetic radiation and spiral into the nucleus. In addition Bohr was not able to explain electrons orbits of large atom w/many electrons.