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.
Electrons move to farther energy levels the more energy an atom absorbs.
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
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.
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.
As you may know, as we move down a column on the periodic table, the atoms get larger because they have more energy levels (which are the floors of our bank). We also have more security guards (protons), but they're all the way in the basement (the nucleus), and they would really have trouble stopping a robber that landed on the roof and is trying to steal money from the top floor. So, the more floors the bank has, the easier it is for the robbers to steal the money from the top floor, because the security guards don't have as much control over the top floors as they do the ones closest to the basement. In chemistry terms, the bigger an atom is, the lower its ionization energy will be. As we move down a column on the periodic table, the atoms get bigger, so as you move down a group (or column) on the periodic table, the ionization energy decreases. This is because those protons are so far away from the outer electrons that their pull is very weak.
Next, we'll compare atoms across a period. Keep in mind that it is only when you move down a column that new energy levels (or floors) need to be added, so we are going to compare banks with the same number of floors but an increasing number of security guards. Which bank do you think will be most difficult to rob: one with two floors and four security guards or one with two floors and ten security guards? I think it would require much more energy to rob a bank with ten security guards than four. So, given the number of floors (energy levels) remains the same, the bank with the most security guards (protons) would be the most difficult to rob. In chemistry terms, given the same number of energy levels, the more protons an atom has, the higher its ionization energy will be, so as you move across a period on the periodic table, the ionization energy increases. Neon has a higher ionization energy than beryllium: neon has ten security guards in two floors, and beryllium only has four security guards in two floors.
Ionization energy decreases when moving down groups; it increases across periods.
The Effects of Ionizing Radiation
Electromagnetic radiation that has the energy of ultraviolet light or higher (X-rays and gamma rays) is damaging to living tissues because it can cause the atoms to lose their electrons. Later on you'll learn that electrons are pretty much the 'glue' that holds bonds together. If bonds start losing electrons, they start breaking. If you have enough bonds that break, especially in DNA, mutations or even cell death can occur. This is both good and bad. DNA mutations from ionizing radiation can cause cancer. However, ionizing radiation can be used in very specific locations in the treatment of cancer by killing cancer cells.
The trends mentioned in this lesson are very general. There are always going to be exceptions here and there. Don't worry about memorizing the exceptions, but do feel comfortable with explaining what the trend is and why.
So, to review: as you move from top to bottom in the same group or column on the periodic table, the ionization energy will decrease, meaning that it will become easier and easier to remove an atom's outer electron. This is because these electrons are being removed from farther and farther away from the nucleus as the atoms increase in size. As you move from left to right in the same period or row on the periodic table, the ionization energy will increase. This is because electrons are all located in the same energy levels, so elements with more protons (those on the right-hand side) will have a greater pull on those outer electrons, making it more difficult to remove them from atoms.
After watching this lesson, you should be able to:
- Define electromagnetic radiation and explain why some of it can be harmful
- Define ionization energy and describe the trend in ionization energy in groups and periods of the periodic table