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Ionic Compounds

Ionic Compounds. Ionic Compounds. Does what it says on the box: an ionic compound is a compound (so, more than one element) made up of ions (charged atoms). These are called “salts” in general. Table salt (NaCl) is just a specific example of a salt. NOT Bonds.

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Ionic Compounds

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  1. Ionic Compounds

  2. Ionic Compounds Does what it says on the box: an ionic compound is a compound (so, more than one element) made up of ions (charged atoms). These are called “salts” in general. Table salt (NaCl) is just a specific example of a salt

  3. NOT Bonds You will frequently see the term “ionic bond” I do not like this phrase; it is misleading. In an ionic compound, there are no bonds. Instead, you have formula units. Example: NaCl If you look at a crystal of NaCl, you find that there are a bunch of Na+ ions and Cl- ions all crammed together in a repeating pattern, but there are no bonds. So….what holds them together?

  4. CHARGES! Opposite charges attract. The Na+ is attracted to all the Cl- around it, and vice-versa. (This is called Coulombic attraction, by the way) There is no such thing as in individual “NaCl”. Instead, “NaCl” is the formula unit—the proportion of sodium to chlorine… 1 to 1

  5. Is it ionic? So how do you know if it’s ionic in the first place? Method 1: experimental Method 2: on paper (Different kind of ionic entirely)

  6. Method 1 Step 1: melt it. (Ionic compounds don’t tend to melt at temperatures below a couple thousand degrees Celsius) Step 2: Shove a battery and light bulb in it. Step 3: Profit Step 3: If it lights up, the compound conducts electricity, which only happens if there’s charges moving…so it must be ionic

  7. Method 2 Look at the formula. Is there a metal? If yes: it’s ionic If no: it’s covalent (the other kind—we’ll get to it) CO2NaCl MgSO4RhO H2O covalent ionic ionic ionic covalent Sc(OH)3 BrCl Na ionic covalent not even a compound in the first place

  8. One of the most important things all year Overall, everything is neutral; charges must balance. If you have a +2, there are two negatives somewhere. This is true of ionic compounds. Examples: NaCl MgO Na is +1 Mg is +2 Cl is -1 O is -2 (these are charges you should know from where they are on the table)

  9. What if I Want Mg2+ with Cl-? This is perfectly ok; I just need to use a different ratio: The formula is MgCl2 I now have two chlorines (-1 each) balancing out the magnesium (+2) Al3+ and Cl-? Just use a 1:3 ratio: AlCl3 Ok, but what about Al3+ and O2-?

  10. Make them Both 6! Al2O3 I now have two aluminums (3+) for every three oxygens (2-) So the total charge of the aluminums is 6+, and the total charge of the oxygens is 6-. Balance! In an ionic compound, the subscripts (2 and 3, in this case), are just the proportion of each ion in the formula unit. If I have 2000 formula units, that’s 4000 aluminum ions and 6000 oxygen ions.

  11. It’s a ratio! Al2O3 Ratios should always be in their lowest possible terms. Ca2O2 does balance (Ca is 2+, O is 2-) but 2:2 is the same as 1:1 CaO is the actual chemical formula.

  12. Important Point CaCl2 This is NOT made of Ca and Cl2; it is one Ca2+ and two Cl-. When an ionic compound dissolves in water, it splits apart into the individual ions. If I put 200 CaCl2 formula units into water, I will have water with 200 Ca2+ ions and 400 Cl- ions all floating around freely.

  13. Summary Ionic compounds are made of charged atoms Held together by charges, not bonds Recognize them by looking for a metal

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