Periodic Trends: Ionization Energy
Learning Objectives
• Define ionization energy.
• Describe how the ionization energy changes within a period.
• Describe how the ionization energy changes within a group.
• Analyze the importance of ionization energy in determining element reactivity
Which animals in the herd are the easiest to hunt?
In any nature show, from the classic “Wild Kingdom” shows hosted by Marlin Perkins to the
modern BBC World-produced series hosted by David Attenborough (“Planet Earth” and “Blue
Planet” are two of the multi-volume examples), there is a sequence (or several) showing a hunt
between predators (plural) and prey (also plural). Lions, tigers, wolves, hyenas, and other well-
equipped carnivores or secondary consumers will systematically attack a group or herd to obtain
their food. As they hunt, whether as an organized pack or in small groups, they must weigh the
need to eat with the need to conserve useful energy, and not be injured or possibly killed in the
process, with no meal to show for it.
As a result, these hunters and predators tend to stay to the outside, looking for the weakest prey
that is closest to the edge, and therefore the easiest to remove.
The low-hanging fruit
It is very likely that you have gone apple-picking, or at least seen someone else participate in the
activity. On fall weekends all over central New England (famously John “Johnny Appleseed”
Chapman hailed from Leominster), orchards open to family festivals where the central activity is
picking apples directly off the trees. Without fail, the first fruits picked are the ones closest to
the picker and easiest to retrieve, or the “low-hanging fruit,” and the trees closer to the entrance
(at the edge of the orchard) are the first attacked by eager toddlers and their families trying to
keep everyone together and not have to worry about wanderers. As the day wears on, trees
situated more toward the center are the next to be exploited in the mad ritual, and eventually
adult shoulders and small platforms or carefully monitored ladders are relied upon to grab fruit
that is higher up in the tree (it depends on what kind of facilities are available, as well as
insurance…) by the end of the weekend, each tree looks like a picture painted by someone who
started at the top and ran out of red paint halfway to the bottom.
In either case, whether one considers the unfortunate (but biologically necessary) fate of a hunted
animal, or the classic experience of a piece of fruit to be enjoyed, the first ones to go are the
easiest ones to obtain and remove, the ones that require the least amount of energy to do so.
Animals or fruits that are more difficult to remove require more energy, and usually that energy
is not available in the system, either because of fatigue, an instinctive calculation, or the rules of
the farm.
