Back To CourseFundamental Biology
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Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.
Each atom is unique because it is made of a specific number of protons, neutrons, and electrons. Usually, the number of protons and electrons is the same for an atom. And while the number of protons will never change for any atom, because this would mean you have a completely different element, sometimes the number of electrons does change. When an atom gains or loses an electron, we get an ion. Since electrons themselves have a net negative charge, adding or removing electrons from an atom changes the charge of the atom. This is because the number of electrons is no longer in balance with the number of protons, which have a positive charge.
Atoms that gain electrons and therefore have a net negative charge are known as anions. Conversely, atoms that lose electrons and therefore have a net positive charge are called cations. Cations tend to be metals, while anions tend to be non-metals. Ions may also be single atoms or multiple, complex groups of atoms.
When we talk about ions, it's true that opposites attract. The opposite negative and positive charges of the ions hold together in ionic bonds, forming ionic compounds, which are just what they sound like: compounds made of ions. The loss or gain from one atom matches the loss or gain of the other, so one atom essentially 'donates' an electron to the other atom it pairs up with.
Think of the pairing of ions like two bar magnets. If you try to put the two north or south ends of different magnets together, they repel each other very strongly; but turn one of those magnets around so that you are putting a south end to a north end, and they quickly snap together. Ions behave similarly. Two positive or two negative ions will not join together because they have the same charge. But one positive and one negative will happily join together to make an ionic compound.
Table salt is an example of an ionic compound. Sodium and chlorine ions come together to form sodium chloride, or NaCl. The sodium atom in this compound loses an electron to become Na+, while the chlorine atom gains an electron to become Cl-. Together, they form a neutral compound because the ions balance each other out. This is true for all ionic compounds - the positive and negative charges must be in balance.
Potassium oxide, or K2O, is another example of an ionic compound. You may have noticed that unlike the sodium chloride example, which has one sodium ion for each chlorine ion, this time there are two potassium atoms for each oxygen. This is because the charges have to be balanced for the ionic compound. All you have to do to determine how many of each ion will be in the compound is take a quick look at the periodic table.
Let's start with our table salt, the sodium chloride. Sodium is in the first column of the periodic table, so it will lose one electron. Chlorine is in the second-to-last column, so it will gain one electron. Each atom in this ionic compound will lose or gain one electron, so they can pair up in a one-to-one ratio.
Now let's go back to potassium oxide. Potassium is in the first column, so it will lose one electron and have a net positive charge. Oxygen, however, is in one column over from where we found chlorine, so it will gain two electrons. This means that in order for potassium oxide to have a net charge of zero, we need two potassium atoms, each with their net positive charge of one to match up with the oxygen that has a net negative charge of two.
Ionic compounds are special because they form lattice or crystalline structures. This formation comes from the ionic bonds that hold the ions together in the compound. Ionic bonds are very strong, which makes them difficult to break apart. Because of this, ions tend to have higher boiling and melting points. If you think about this, it makes sense because melting and boiling are two ways that we can break bonds within molecules.
Ions also tend to dissolve in water quite easily. Remember how the opposite charge of ions attract them to each other? The opposite is true for dissolving them - like dissolves like. Water is a polar substance, which means that one end of the molecule has a different charge than the other end. This is similar to our bar magnet - each pole has a different charge, which is exactly why trying to put north to north or south to south doesn't work.
So, just how does water break apart these strong ionic bonds? When something is put into water, it becomes surrounded by it. And when the oppositely charged atoms of the submersed ionic compound are surrounded by the opposite charges of the polar water molecules, the ions are pulled apart into the liquid. When the pull is stronger than the pull of the ionic bonds within the molecule, the ions dissolve in the water.
You can try this at home with some salt. If you put a spoonful of salt into a glass of water and stir it up, the salt breaks apart and dissolves into the water. But take that same glass of water and let it sit out for a few days, and you'll notice the salt at the bottom of the glass once all the water evaporates. Though the polar water breaks it down, it doesn't become part of the water, so it gets left behind as the water evaporates into the air.
One thing that's important to keep in mind is that the individual ions are much different than the compounds they form. Salt is made of sodium, a metal, and chlorine, which is a gas; but put them together, and they form salt, something that is much easier for us to swallow!
Ionic compounds are compounds made up of ions. These ions are atoms that gain or lose electrons, giving them a net positive or negative charge. Metals tend to lose electrons, so they become cations and have a net positive charge. Nonmetals tend to gain electrons, forming anions that have a net negative charge.
Just like opposite poles of a magnet attract, so do opposite ionic charges. Ions of opposite charge are held together by very strong ionic bonds within the compound. These bonds form a unique crystal lattice structure, making them difficult to break. However, put these compounds in a polar substance like water, and the opposite charges that surround it are able to break apart the ions and dissolve them into the liquid.
Ionic compounds must be balanced - the sum of the positive and negative charges must equal zero. But while the charges of an ionic compound are the sum of their parts, the substance that is formed is quite different. Separately, you would not want to eat sodium as a metal or chlorine as a gas. But put them together in salt, and they make a tasty addition to that order of fries you had for lunch!
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Back To CourseFundamental Biology
36 chapters | 333 lessons