Ionization Energy: Trends Among Groups and Periods of the Periodic Table Video

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  • 0:06 Ionizing Energy
  • 0:53 The Electromagnetic Spectrum
  • 1:58 Ionization
  • 3:13 Group and Period Trends
  • 6:05 The Effects of…
  • 6:45 Lesson Summary
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Lesson Transcript
Instructor: Kristin Born

Kristin has an M.S. in Chemistry and has taught many at many levels, including introductory and AP Chemistry.

Do you know someone who has undergone radiation as a form of cancer treatment? Have you ever thought about why X-rays have health risks? Watch the video to find out what these types of radiation are really doing to atoms, define ionization energy and identify ionization trends on the periodic table.

Ionizing Energy

Electrons move to farther energy levels the more energy an atom absorbs.
Atomic Energy Absorption

One day you decided to climb a tree in your backyard. Maybe you were eight years old; maybe it was yesterday. Either way, you overestimated your climbing abilities, and just as you were reaching that top branch, you tumbled to the ground. A few painful hours later, you're in an X-ray room, covered in a lead apron, waiting for your arm to be X-rayed. Why did you have to wear that lead apron? What's all the fuss about X-rays? You couldn't feel them. They didn't hurt when the pictures were being taken. What were they doing to your arm? In this lesson, we're going to cover just what those X-rays were doing to the atoms in your arm and what makes X-rays potentially harmful. We're also going to expand this knowledge to the periodic table so we can use it to make predictions about atoms.

The Electromagnetic Spectrum

Earlier you learned that when an atom absorbs energy, its electrons move out to outer energy levels. The more energy an atom absorbs, the more energy the electron absorbs and the farther out it will go. I may have left you with an unanswered question, though, because I never did tell you what happens when an atom absorbs too much energy. I'm about to explain that, but first, let's start out by reviewing some of the forms of electromagnetic radiation - this is the source of the energy.

Electromagnetic radiation is just a form of energy that travels through space. There are many different kinds that have different amounts of energies. For example, all visible light has a medium amount of energy, red light having the lowest and violet light having the highest. Electromagnetic radiation that has even more energy than violet light is ultraviolet (UV) light. You may know that UV light can be bad for you, but the reason is that it carries very high amounts of energy. Higher than UV is energy from X-rays, and even higher than that is radiation from gamma rays.


The electromagnetic radiation spectrum
Electromagnetic Radiation Spectrum

So, what do all these forms of electromagnetic radiation do to atoms? The forms that have low energies just excite the electrons of atoms, which cause them to move out to higher energy levels, eventually falling back down and releasing energy. However, if too much energy is added to an atom, the electrons won't just go out to a higher energy level, they'll leave the atom altogether! That's it. Gone.

So, just how much energy does it take to remove electrons from an atom? Well, that depends on the type of atom. This amount of energy is so important that it has a special name: ionization energy. Ionization energy is the amount of energy required to remove an electron from an atom. The electron that is most likely to leave the atom first is the one that's the farthest out already, so when it becomes ionized, it is losing an outer electron. Because each atom is structured a little bit differently, each atom will have a different ionization energy. You won't need to memorize the specific amounts of energy for each atom, but you should be able to identify and explain ionization energy trends as you move down groups or across periods on the periodic table.

Group Trends

Remember, a group on the periodic table is just a column. We're first going to compare the ionization energies of atoms in the same column. To do this, I want you to imagine that an atom is a bank filled with security guards in the basement - these are going to be protons in the nucleus. The electrons will be represented as money located on different floors of the bank, which are our energy levels. Robbers are trying to steal this money, which would cause the bank to be ionized. Also, it should make sense that the easier something is, the less energy it takes to do it. So, we are going to determine how easy it will be for the robbers to steal the money from the bank or how easy it is to remove an electron from an atom.

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