Thursday, December 1, 2011

Chemistry Thursday: Ionic bonding and salts!

Atoms are the building blocks of all molecules, so we need to know a little about them to understand how molecules work. An atom is happiest when it has eight electrons on its outer shell. (This is called the octet rule and it applies to the elements we'll get to know the best - those under number 20 - up to calcium.) If an atom has less than eight, it gets seriously desperate and it goes on a mighty quest for another electron!

This is one of the reasons the noble gases are so stand-offish. Neon, argon, helium - they have 8 electrons in their outer shells, so they have no need to interact with those common elements to get electrons. They're the haves of the periodic table

Let's say you're sodium and you have an extra electron (the + on the element listing). You really want eight electrons, so you go out on the town hoping to attract another atom who needs another electron or has seven to share. Hey, chlorine! You're looking mighty attractive with those seven extra electrons. Can I buy you a drink? And before you can say I could have had a V8, we have sodium chloride (NaCl).

Generally, when you see something like that + (with or without numbers) in the right hand corner for sodium, that means we have an extra electron, or two, or three. Generally, when you see a minus sign (-, with or without numbers), this means that we are missing electron(s) in the outer shell. 

The general process is this...The outer orbital of one of the atoms has a vacancy - in this case, chlorine - which means it can collect an electron and complete that octet. The nucleus of the chlorine offers the sodium a tighter bond, so the sodium gives up its electron. Ionic bonding relies on electrostatic attraction between the atoms to work.

Electrostatic attraction: "Electrostatic attraction is the attraction that an atom has for electrons." Now, I realize we're going in circles here, but this is the best definition I could find that doesn't require my brain to hurt too much this early in the morning. So the sentence above could be re-written as, "Ionic bonding relies upon the attraction that an atom has for electrons to work". Sounds good to me!

This process is called ionic bonding. It generally only happens between a cation (positively charged atom, usually a metal from the right hand side of the table) and an anion (negatively charged ion, usually a non-metal from the left hand side of the table).

Click on the link to see some cute animations of various atoms coming together in ionic bonding!

When sodium and chloride come together we get a salt. (Definition: Salts are ionic compounds composed of a positively charged or cationic ion and a negatively charged or anionic ion. They are electrically neutral. The positively charged ion is a metal, like sodium or calcium, and the negatively charged ion is a non-metal, like chlorine or sulfur.) We can get other salts, too. Magnesium sulfate (or Epsom salts), sodium sulfate (Glauber's salts), copper (II) sulfate - the one to your left, so pretty!) and so on - there are so many salts out there and so many ways to create them! I bet you didn't think salt could be fun, but it is!

Join me next week for covalent bonding!

Point of interest! There's a new list on the blog called chemistry links! I'll be putting these posts on that page in the proper order so you can refer back to it, and you'll find links to any chemistry related posts on the blog in that section!

I love this interactive periodic table! Bookmark it and use it! It's great (and some of it is lime green!) 


Lesley said...

Thanks! Great explanation

Ellbie said...

I once had a professor describe bonding as this: Ionic bonding is like a couple living together, you are very happy at the moment but if another attractive ion comes along, with the right charge, then it is like I'm outta here baby. On the other hand covalent bonding is more like marriage, it takes energy (ie. guns, lawyers,or money) to break that bond.