Hey there, <span>The ionization energy decreases from top to bottom in groups, and increases from left to right across a period.</span> Helium<span> has the largest first ionization energy, while </span>francium<span> has one of the lowest. </span> Hope this helps :))
<span>By definition, the first ionization energy is the energy required to remove the most loosely held electron from one mole of gaseous atoms to produce 1 mole of gaseous ions each with a charge of 1+. </span><span />