 In this video, we will be talking about ions. This picture shows a neutral oxygen atom. A neutral atom is an atom with the same number of protons as electrons. This oxygen atom has eight protons and eight electrons, and since the number of protons equals the number of electrons, this atom is neutral. But if we were to take one electron off, this would not be a neutral atom anymore. This would become an ion. An ion is an atom that has a positive or negative charge because it has gained or lost one or more electrons. In this example, there are more protons than there are electrons. We have eight protons, but only seven electrons. Since there are more positive charges than negative charges, the atom is now what we call a positive ion. And since there is one more proton than there are electrons, we say the ion has a charge of plus one. In chemistry, we often call positive ions cations. Here's a handy trick to remember. Cat ions are always positive. Cats have paws, get it? Let's go back to our neutral oxygen atom again. What happens if we add an electron? Because there are now more electrons than there are protons, and because electrons have a negative charge, we say this is a negative ion. Since there's one extra electron, we say this ion has a charge of minus one. And if we added another electron to this atom, the atom would have a charge of minus two. Chemists call negative ions anions. You can remember this because there's an N in it that stands for negative. When ions are formed, atoms tend to want to lose enough electrons or gain enough electrons so that their outer shell is filled. This makes them more stable. In general, elements on the left side of the periodic table tend to lose electrons to become cat ions or positive ions. On the right side of the periodic table tend to gain electrons to form anions, also called negative ions. Let's look at the first row of the periodic table for some examples. Lithium tends to lose one electron to get a full outer shell. Lithium loses its entire second electron shell. Lithium develops a charge of plus one since it now has one more proton than it does electrons. Beryllium will lose two electrons. Just like lithium did, it will lose its entire second shell. Because there are two more protons than there are electrons, beryllium will develop a charge of plus two and it will also lose its entire second shell. Because it has three more protons than it does electrons, it will develop a charge of plus three. Now let's go to the right side of the periodic table. Neon, which is a noble gas, already has a full outer shell. This makes it very stable. Neon and other elements in the noble gases column, like helium and argon and krypton etc., do not form ions easily. Now let's look at fluorine. Fluorine has seven protons, so a neutral atom of fluorine will have seven electrons. Fluorine tends to gain one electron, so that it has a full outer shell with eight electrons in it. This gives it one more electron than it has protons, and because it has more electrons than protons, it is a negative ion. Fluorine gained one electron, so it has a charge of negative one. A neutral atom of oxygen has six electrons. In order to have a full outer shell, oxygen needs to gain two more electrons. It will develop a charge of minus two. Oxygen needs to gain three extra electrons to build a full outer shell. It will develop a charge of minus three. Carbon typically doesn't like to gain or lose electrons, so we don't often see it as an ion. So why should we care? We care about ions because they make up a lot of compounds that are very important in our everyday lives, like the salt we put on our popcorn, and the baking soda in your cookie recipe, and the bleach you use to clean your house, and the fluoride in your toothpaste, and many other things. Ions are also very important in many types of chemical reactions. In summary, an ion is an atom that has a positive or negative charge because it has gained or lost one or more electrons. A charge develops when an atom does not have the same number of protons as it does electrons. Atoms with a positive charge are called cations. Atoms with a negative charge are called anions. When they form ions, atoms tend to lose or gain as many electrons as they need to to have a full outer shell.