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 neutral 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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