电离，原子和离子半径，电负性，电子亲和力和金属度，遵循元素周期表的趋势。电离能量通常在元件周期（行）上从左向右移动。这是因为原子半径通常在一段时间内减少移动，因此在带负电的电子和带正电的原子核之间存在更大的有效吸引力。对于表格左侧的碱金属，电离处于最小值，对于一段时期最右侧的惰性气体，电离处于最大值。惰性气体具有填充的价壳，因此它可以抵抗电子去除。电离减少从元素组（列）向上到下移动。这是因为最外层电子的主量子数在一组中向下移动。原子中有更多的质子向下移动（更大的正电荷），但效果是拉入电子壳，使它们变小并从核的吸引力中筛选外部电子。沿着一组向下移动添加更多的电子壳，因此最外面的电子变得越来越远离原子核。
澳洲维多利亚大学Essay代写：电离能定义和趋势
Ionization, together with atomic and ionic radius, electronegativity, electron affinity, and metallicity, follows a trend on the periodic table of elements. Ionization energy generally increases moving from left to right across an element period (row). This is because the atomic radius generally decreases moving across a period, so there is a greater effective attraction between the negatively charged electrons and positively-charged nucleus. Ionization is at its minimum value for the alkali metal on the left side of the table and a maximum for the noble gas on the far right side of a period. The noble gas has a filled valence shell, so it resists electron removal. Ionization decreases moving top to bottom down an element group (column). This is because the principal quantum number of the outermost electron increases moving down a group. There are more protons in atoms moving down a group (greater positive charge), yet the effect is to pull in the electron shells, making them smaller and screening outer electrons from the attractive force of the nucleus. More electron shells are added moving down a group, so the outermost electron becomes increasingly distance from the nucleus.