Reading Notes
for Chapter 2
These are Dr. Bodwin's reading notes for Chapter 2 of "Chemistry
2e" from OpenStax.
I am using a local .pdf copy that was downloaded in May 2020.
Chapter
Summary:
What kind of stuff is stuff made of? This chapter has a LOT of material
that we will be using as our "language" of chemistry throughout the
course. There are quite a few rules and lists in this chapter that
people often think about as just something to memorize, but it's all
information that you will probably be using regularly enough that it
becomes part of your natural memory.
Bad Chemistry Joke of the Chapter: Never trust an atom, they make up everything.
Dalton's Atomic Theory:
This
is an excellent example of what a theory is. Using the best available
information at the time, Dalton compiled an explanation that was
consistent with that information. It's pretty amazing. As technology
has advanced and the information we are able to observe about matter
has become more detailed, there are a number of part of Dalton's Atomic
Theory that aren't quite correct so they have been updated and
clarified by subsequent atomic theories. That's how scientific
knowledge is developed, tested, refined, and grown!
The laws of definite proportion/constant proportion/multiple
proportions are observations that distinguish between "compounds" and
"mixtures" as discussed in Chapter 1. Compounds are substances that
have a very specific number of atoms (elements) combined in a constant
ratio. If you change the ratio, you change the compound.
Atomic Theory and Structure:
There are lots of animations and videos that look at atomic theory
online, search "atomic theory animation" and you'll find a ton that are
aimed at different audiences. One that I found is:
https://www.learner.org/series/chemistry-challenges-and-solutions/atoms-and-light-exploring-atomic-and-electronic-structure/models-of-the-atom/
To define different atoms, we need to keep track of the subatomic
particles and what they tell us. Protons define the identity of the
element, neutrons (with protons) define the mass and isotope of the
atom, electrons define the charge of the atom or ion.
Atomic number, mass number, and charge are ways to keep track of the subatomic particles.
Chemical Symbols and the Periodic Table:
Chemical
symbols including atomic number, mass number, and charge tell you
everything you need to know about the subatomic particle makeup of an
atom.
The Periodic Table is arranged by atomic number... we'll get into a
bunch of different things the Periodic Table can tell you as we work
through the next few chapters.
NOTE - I do not expect anyone to sit down and memorize the Periodic
Table just for the sake of memorizing the Periodic Table. If you want to do that, go ahead. I do
expect that you will remember a number of the common elements because
you will be using them very often or they are in very common usage
outside of a chemistry classroom context. When I use an uncommon
element in a homework or quiz question, I will often give its atomic
number to help you find it on the Periodic Table, so as long as you
know what atomic numbers are, you should be able to find the element.
Learning the group names of the Periodic Table can be quite useful. Figure 2.27.
Chemical Formulas:
Back to the "compounds" from Chapter 1 and the laws of proportion from
earlier in this chapter, a chemical formula describes the whole number
ratio of different elements in a compound.Practice reading, writing,
and interpreting these because we will be using them constantly
throughout the course.
Ionic vs Covalent - Here's an important distinction to get figured out.
Ionic interactions occur between charged species; covalent interactions
involve sharing electrons in a "bond".
Ionic interactions tend to occur between elements that are farther
apart on the Periodic Table (like sodium and chlorine); covalent
interactions tend to occur between elements that are closer to each
other on the Periodic Table (like carbon and oxygen).
You can have BOTH ionic AND covalent interactions within the same compound (like sodium carbonate).
Species that only experience covalent interactions are called molecules.
NOTE - I do expect you to memorize the polyatomic ions in Table 2.5. It looks like a long list, BUT:
- If you look at the systematic nomenclature rules (right after the
table), you'll see that a bunch of the oxoanions in the list are
redundant (if you know the naming rules). For example, if you
"memorize" that sulfate is SO4-2, then (by using the naming rules) you also know that sulfite is SO3-2.
- My hope is that, at least for some of the more common polyatomic
ions, you will use them often enough that you just remember them rather
than specifically trying to "memorize" them. For example, I will
probably use nitrate in half the examples and homework problems in this
course. After looking it up 20 or 30 times, you'll just remember that
nitrate is NO3-1.
- There are a couple others that you might see, but if you have all
those in the table, you'll be able to handle them. A few specific
"extra" polyatomic ions: bromate & iodate (same as chlorate),
phosphite, thiocyanate, and thiosulfate.
Chemistry nomenclature seems like it has a lot of rules, but it's
something that really does get easier with just a reasonable amount of
practice. The biggest thing to remember is that for ionic compounds,
the total positive charge must equal the total negative charge
Memorizing polyatomic ions and practicing chemical formulas and
nomenclature are a couple cases where flashcards work extremely well
for many students. Literally, flashcards with one thing written on one
side and the "answer" written on the other. Make yourself a stack (or 2
or 3...) and go through them whenever you have a few minutes to spare.
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Bodwin,
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