write any 100 ionic compounds with formulas..

Ionic compounds are basically defined as being compounds where two or more ions are held next to each other by electrical attraction. One of the ions has a positive charge (called a "cation") and the other has a negative charge ("anion"). Cations are usually metal atoms and anions are either nonmetals or polyatomic ions (ions with more than one atom). Think back to grade school: The same thing that makes the positive and negative ends of a magnet stick to each other is what makes cations and anions stick to each other.

Usually, when we have ionic compounds, they form large crystals that you can see with the naked eye. Table salt is one example of this - if you look at a crystal of salt, chances are you'll be able to see that it looks like a little cube. This is because salt likes to stack in little cube-shaped blocks.

Sometimes when you see a salt, it looks like a powder instead of a cube. This doesn't mean that the salt is not a crystal - it means that the crystals are just so small that you can't see them with the naked eye. If you were to put the powder under a microscope, chances are that you would see little geometric blocks. 

So, what are the main properties of salts? Well, I'm sure glad you asked...

  • All ionic compounds form crystals. So far as I know, there are no exceptions to this. Again, salts like to form crystals because when you have a whole bunch of little electrical positive and negative charges all stuck together, they seem to like to bunch into little stacking groups. The arrangement that these ions like to stack into is different, and is referred to as the "unit cell". There are ten or so different general shapes of unit cells. When you get to graduate school, ask me about them. For high school classes, it's really not all that important.
  • Ionic compounds tend to have high melting and boiling points. When I say "high", what I mean is "very, very high." Most of the time, when you work with ionic compounds in a chemistry class, the melting point is hot enough that you can't melt them with a Bunsen burner.  So, why are these temperatures so high? Well, it has to do with the way that ionic materials are held together. Remember how we said above that ionic compounds form crystals? These crystals are basically just great big blocks of positive and negative charges all stuck together. To break the positive and negative charges apart, it takes a huge amount of energy. This means that if we heat up the compound to add energy, it takes a huge amount of energy to break it apart.
  • Ionic compounds are very hard and very brittle. Again, this is because of the way that they're held together. Above, we said that it takes a lot of energy to break the positive and negative charges apart from each other. This is the reason that ionic compounds are so hard - they simply don't want to move around much, so they don't bend at all.  This also explains the brittleness of ionic compounds. It takes a lot of energy to pull ionic charges apart from each other. However, if we give a big crystal a strong enough whack with a hammer, we usually end up using so much energy to break the crystal that the crystal doesn't break in just one spot, but in a whole bunch of places. Instead of a clean break, it shatters. 
Ionic compounds conduct electricity when they dissolve in water. If we take a salt and dissolve it in water, the water molecules pull the positive and negative ions apart from each other. (This is because of the unusual properties of water, but that's a different story for a different time). Instead of the ions being right next to each other, they wander all over the water.  Now, think back to what electricity is - hopefully, you remember that electricity is just the movement of electrons through metals (or anything else). Now, electrons are just negatively-charged particles, and metals have the property that they're good at letting them wander around. Dissolved salts are the same way. When you dissolve the salt in the water, the positive and negative ions in the water allow electrons to flow much better than if you just had water by itself. Voila! Salt water conducts!  A question you might have is "Does electricity travel through salt crystals?" Nope. It doesn't. Because the ions are stuck in one place due to the structure of the crystal, the electricity doesn't move around very well.  Another good question: "Does water without salt in it conduct electricity?" The answer: Not very well. Water by itself is a lousy conductor. The reason that boneheads who put the hairdryer in the bathtub with them turn into human fritters is that when they wash themselves, all the crud on them gets dissolved in the water. Some of the crud is ionic, so when the dryer hits the water, they get zapped. An interesting "thought experiment" would be to wash all the salt off yourself and then drop a hairdryer in the bathtub with you. In theory, you would be fine. In real life, you'd still become a crispy critter because tap water by itself has ionic compounds dissolved in it anyway.
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It is very simple to write the ionic formula once you get the basic concept. I know you said you understand the charges, but I'm not sure how much you know, so I'm going to start from the beginning. If you look on a periodic table, the first column from the left will form +1 ions, and the second will form +2. The elements in between (the shorter columns) are transition metals and their charge changes and will usually be given to you. If you approach the periodic table from the right, the SECOND column forms a -1 ion, the third forms a -2 and the fourth forms a -3. The idea is that each element in the compound will form ions--one of which will have a positive charge and the other a negative, so they will bond together.

When you are given a formula to write--let's say Magnesium chloride, you need to determine what charge the ions will have. Magnesium is in the 2nd column from the left, so it will have a +2 charge. Chlorine is in the second column from the left, so it will have a -1 charge. When you are writing a compound you must have a net charge of 0. This means that the charge of the two elements should add up to be zero. In the case of Magnesium chloride, we need to have two chlorines 2 x -1 to balance out the +2 of the magnesium. 2 + -2=0. So, your compound is MgCl2 (the 2 is a subscript). Also, it is important to note that adding -ide to the end of the nonmetals (the columns on the right side of the periodic table) makes them ions, which is why it is magnesium chlorIDE and NOT chlorine.

Sometimes, it can get a little more complex--let's say we have Magnesium nitride, although I'm not sure this compound actually exists, it's a good problem to try. Magnesium, again, will have a +2 charge, but the nitrogen will have a -3 charge. Somehow we have to combine these in a way that it will have a net charge of 0. If you have already covered balancing equations, this should be simple. It is also similar to finding common denominators in math. multiply the +2 charge by 3, and the -3 charge by 2. Your compound is Mg3N2 (the numbers again as subscripts). Magnesium: 3 x 2 =6, Nitride: 2 x -3=-6
6+-6 = 0.

Also, if you haven't already, you will be getting into polyatomic ions. You will know the charges on these ions and it is the same concept, only with more elements. If you need to multiply a polyatomic ion, make sure to have parentheses before the subscript. For example: Barium hydroxide is Ba(OH)2. You cannot split up the hydroxide (OH-) since it is a polyatomic ion.

Technical point on writing the formulas: the metallic ion will always be written first; ionic compounds are almost always a metal and a nonmetal combined.
I hope this at least gives you a basic idea of the concept.

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hi

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First of all, there will never be a superscript if all you are doing is writing ionic compounds.It is very simple to write the ionic formula once you get the basic concept. I know you said you understand the charges, but I'm not sure how much you know, so I'm going to start from the beginning. If you look on a periodic table, the first column from the left will form +1 ions, and the second will form +2. The elements in between (the shorter columns) are transition metals and their charge changes and will usually be given to you. If you approach the periodic table from the right, the SECOND column forms a -1 ion, the third forms a -2 and the fourth forms a -3. The idea is that each element in the compound will form ions--one of which will have a positive charge and the other a negative, so they will bond together.When you are given a formula to write--let's say Magnesium chloride, you need to determine what charge the ions will have. Magnesium is in the 2nd column from the left, so it will have a +2 charge. Chlorine is in the second column from the left, so it will have a -1 charge. When you are writing a compound you must have a net charge of 0. This means that the charge of the two elements should add up to be zero. In the case of Magnesium chloride, we need to have two chlorines 2 x -1 to balance out the +2 of the magnesium. 2 + -2=0. So, your compound is MgCl2 (the 2 is a subscript). Also, it is important to note that adding -ide to the end of the nonmetals (the columns on the right side of the periodic table) makes them ions, which is why it is magnesium chlorIDE and NOT chlorine.Sometimes, it can get a little more complex--let's say we have Magnesium nitride, although I'm not sure this compound actually exists, it's a good problem to try. Magnesium, again, will have a +2 charge, but the nitrogen will have a -3 charge. Somehow we have to combine these in a way that it will have a net charge of 0. If you have already covered balancing equations, this should be simple. It is also similar to finding common denominators in math. multiply the +2 charge by 3, and the -3 charge by 2. Your compound is Mg3N2 (the numbers again as subscripts). Magnesium: 3 x 2 =6, Nitride: 2 x -3=-66+-6 = 0.Also, if you haven't already, you will be getting into polyatomic ions. You will know the charges on these ions and it is the same concept, only with more elements. If you need to multiply a polyatomic ion, make sure to have parentheses before the subscript. For example: Barium hydroxide is Ba(OH)2. You cannot split up the hydroxide (OH-) since it is a polyatomic ion.Technical point on writing the formulas: the metallic ion will always be written first; ionic compounds are almost always a metal and a nonmetal combined.I hope this at least gives you a basic idea of the concept.

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