Reading Notes for Chapter 3

These are Dr. Bodwin's reading notes for Chapter 3 of "Introduction to Chemistry". I am using a local .pdf copy that was downloaded in August 2020.

Chapter Summary:

Most of chemistry takes place in the electron clouds around atoms. The way in which those electron clouds interact defines most of the behavior of a material. One extreme involves the transfer of electrons from one atom to another. After electrons are lost or gained, the resulting charged particles (called ions) interact strongly.
STUDY NOTE: Many of the things we are looking at are what I categorize as "flashcard material". If you're not a fan of flashcards, give them another try. I personally prefer actual physical flashcards that I can keep in my bag and flip through when I've got a few moments of downtime (waiting for an appointment, riding the bus, rebooting my computer...), but there are also a lot of flashcard apps and websites where you can make your own flashcards or use sets of flashcards that others have made. Search "flashcard maker" and you'll get a bunch of hits.

Types of Bonding:

"Bonds" are just interactions between atoms.
Noble gases are exceptionally stable because they have an exceptionally stable number of valence electrons.
If other elements on the Periodic Table can achieve the same number of electrons as a noble gas either by gaining, losing or sharing electrons, then they will also be stable.
The Octet Rule is a handy tool, but it's not infallible... Don't fall completely in love with it, there are plenty of cases that violate it.
When atoms gain or lose electrons, they become ions and interact via ionic interactions (often called ionic "bonds")
When atoms share electrons, they are held together by covalent bonds (that's Chapter 4...)
Opposite charges attract one another, like charges repel one another.

Ions:

Check the balance between protons (positive charge) and electrons (negative charge). If there are more protons than electrons, the resulting cation is postively charge; if there are more electrons than protons, the resulting anion is negatively charged.
Charges for monoatomic ions can be often predicted from their position in the Periodic Table. Textbook Table 3.3)
Lewis Dot Diagrams show the valence electrons around an atom.
For elements which can have more than one stable charge, the charge must be specified when describing the ion ("iron plus two")

Ionic Formulas:

In nature, there is a significant energy "cost" associated with separating and isolating charges. I can't go to the stockroom and pick up a bottle of sodium ions because having that many cations without any anions to balance the charge would be extremely unstable.
Ionic formulas are all about balancing the charge... for every unit of positive charge, there must be a unit of negative charge.
Sodium chloride has the formula NaCl because sodium ions have a +1 charge and chloride ions have a -1 charge. By having one of each, the charges balance each other and form a stable ionic compound. If we tried to make "NaCl₂", there would be too much negative charge and the Universe would explode (OK, the Universe wouldn't explode, but it would be a very unstable substance!)

So how do you know if something is an ionic compound? Once in a while you'll run across a tricky one, but most of them are pretty obvious. The three most important things to look for are:

Does the formula contain a metal and a non-metal? Probably ionic, but not always. It gets a little fuzzy when we're on the border (metalloids) or low in the Periodic Table.
Does the formula comtain a polyatomic ion? If it has a polyatomic ion, it pretty much has to be ionic.
If no polyatomic ions are present, are the elements far apart from each other on the Periodic Table? The farther apart two elements are, the more likely they are to form ionic compounds. Potassium and oxygen? Pretty far apart, definitely ionic. Carbon and nitrogen? They're neighbors! Almost NEVER ionic!

Exception (sort of)... if the two elements are close to each other on the Periodic Table and are both metals, then they very likely may be exhibiting metallic bonding. You probably won't run into too many of these, but it is another type of bonding that we will mention here but not really explore in this class...

Naming Ionic Compounds:

Nomenclature is another language. Just like any other language that you might try to learn, it takes practice, repetition, and lots of mistakes along the way.
The textbook has nice rules and examples, so I won't repeat them just for the sake of adding more words to this page.
Remember, the whole point of a nomenclature system is to clearly, concisely, and unambiguously describe something so that the person hearing the name will have the same picture in their head as you do.

Polyatomic Ions:

Polyatomic ions are groups of atoms that are held together with covalent bonds (so within themselves they are like molecules), but which have an overall residual charge (so the interact with other ions like ionic compounds).
This is one of those things that just has to be memorized. Make up a set of flash cards and run through them a couple times a day.
Here's a blog post on the polyatomic ions you are responsible to know: https://chemistryingeneral.blogspot.com/2012/06/polyatomic-ions.html
Ultimately, the best way to memorize polyatomic ions is to practice. After you look up the formula for "nitrate" for the 20th time, you'll probably start to remember it without having to look it up. At the same time, spending some time deliberately memorizing polyatomic ions will save you the time you would have used to look up nitrate 20 times, so I suggest doing some intentional memorizing and practicing enough to lock these names and formulas into your brain a bit.

Formula Mass:

When we're dealing with individual elements, the atomic mass is a useful number to find out how much of the substance we have. When we're working with ionic (or covalent) compounds, we need to determine the formula mass by looking at all of the atoms that make up a substance.
If this wasn't a chemistry class, this would probably be so obvious that you would even have to think about it, but sometimes people try to make formula masses hard just because they're "chemistry". Let's look at an example:
A bicycle wheel and tire has a mass of 2.1kg. The frame and all the hardware of the bike has a mass of 9.2kg. How much does the whole bike (frame + 2 wheels) weigh? Well, that looks like 9.2kg + 2.1kg + 2.1kg = 13.4kg!
Now let's change it from a bicycle to an ionic compound... What is the formula mass of calcium chloride?
Looking at the P.T., calcium should lose 2 electrons to become a +2 cation, and chloride gains 1 electrons to become a -1 anion, so the formula for calcium chloride is CaCl₂. Looking at the P.T. again, the atomic mass of Ca is 40.078g/mol and the atomic mass of Cl is 35.453g/mol... so the formula mass for CaCl₂ is 40.078g/mol + 35.453g/mol + 35.453g/mol = 110.984g/mol

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