Reading Notes
for Chapter 6
These are Dr. Bodwin's reading notes for Chapter 6 of "Chemistry
2e" from OpenStax.
I am using a local .pdf copy that was downloaded in May 2020.
Chapter
Summary:
Almost all of what we call "chemistry" takes place in the electrons.
Protons in the nucleus are critically important because they define the
identity of the element; neutrons are important for a number of
reasons, the most basic of which is to define (with protons) the mass
of an atom, but electrons
are involved in almost all chemical reactions and transformations and
they help us make a variety of predictions about physical properties,
microscopic shapes, reactivity, and stability. Because electrons are so
important to almost all of chemistry, it is important that we look more
closely at them and develop ways to "address" the individual electrons
in an atom, ion, or molecule.
Electromagnetic Energy:
There are a wide variety of energy forms, but it is important to
realize that (for the most part) these are all just different regions
of the same "big picture", the electromagnetic spectrum. The microwaves
that heat up your lunch, the ultraviolet rays that cause damage to your
skin, and the light that lets you read these words are all just
different parts of the electromagentic spectrum.
Waves, whether electromagnetic or otherwise, have some defining
qualities that describe their energy. Frequency, amplitude,
wavelength... all are useful in determining the "energy" of a specific
wave of electromagnetic radiation. Frequency and wavelength are related by the speed of light.
The energy of a specific radiation can be calculated from its frequency and Planck's Constant using E=hv
For our purposes, the reason we need to have a good, fundamental
understanding of energy is because we study matter by observing how
energy changes when it interacts with that matter.
Particle-wave duality - this one is a head-scratcher. Electromagnetic
radiation bahves like a wave when we do some experiments, but it
behaves like a beam of particles in other experiments. The best
explanation for this was that electromagnetic radiation is just
something special that can behave like both a particle and a wave,
hence the particle-wave duality
Photoelectric Effect:
The photoelectric effect is a great example of "quantized energy". The easiest physical
description or analogy of quantized energy levels is comparing a ramp
to a flight of stairs - the ramp is continuous, the stairs are
quantized.
The photoelectric effect is a clear demonstration that the energy with which electrons are help is quantized. These quantized electron energy levels for the basis for our understaning of the electronic stucture of atoms.
Quantum Mechanics:
Quantum mechanics is a vast and complex field, but there are a number
of things we can extract and use to help our understanding of electrons.
The Dr. Quantum video is really quite good (https://www.youtube.com/watch?v=Q1YqgPAtzho)
deBroglie Wavelength - this is a fun little party game... macroscopic
particles have wave-like behaviour, and the deBroglie equation can be
used to calculate the wavelength. How fast does a golf ball have to be
going to develop a measurable wavelength?
Electron Orbitals:
Orbitals are probability surfaces or areas. This is well described in Figure 6.20
Each electron in an atom (or ion) is unique. To study them, we need a
consistent way to provide an "address" for each individual electron.
This is the whole point of quantum numbers - to provide a unique
address system,
If you're a "rule follower" type, quantum numbers are great because
they have very specific and well-defined rules as summarized in Table
6.1.
Although quantim numbers are a very good address system, they can
sometimes get lost as a sea of numbers, so we use some specialized
"shorthand" to help us out. The "angular momentum quantum number"
defines the type of orbital,
so rather than using numbers, chemists tend to use letters (s, p, d,
f), so an orbital with l=0 is referred to as a "s orbital" regardless
of the value of n.
Electron Configurations:
A full set of quantim numbers for a given electron provides a LOT of
information, often more than we really need to make some useful
predictions. Specifically, for many purposes, the value of the magnetic
quantum number really isn't all that informative and the value of the
spin quantum number is only important in the context that there can be
only 2 electrons in each "orbital".
Electron configurations are quantum number shorthand that only includes
the most important details, with the finer details left to the reader
to define if they become necessary.
"Core" vs "Valence" electrons - "core" electrons are full electronic shells like those present in a noble gas. Valence electrons are those that are outside the core.
Most chemistry takes place in the valence electrons.
Predicting Behaviour & Properties:
The arrangement of the Periodic Table might make a little mroe sense
now... The forst 2 columns are often called the "s-block", the
transition metals are the "d-block" and the main group elements are the
"p-block" because that is the orbital type that houses the valnce
electrons in each block.
Whenever predicitng stable electronic configurations, look for full
shells, full subshells, and half-full subshells. These tend to be
relatively stable. For example, tin atoms have a valence electron of
[Kr]5s24d105p2. From this electron
configuration, we could lose 2 electrons (the "5p" electrons) to form a
+2 ion that only has full subshells. It turns out Sn(II) is a
relatively stable ion. Similarly, if we lose 2 more electrons (the "5s"
electrons), we woul dbe left with a full-subshells-only ion with +4
charge... and Sn(IV) is a relatively stable ion!
There are a number of size-based trends that we can explain with the shell/subshell model.
Ionization Energy - the energy required to remove an electron from an atom or ion.
Electron Affinities - the energy associated with adding an electron to an atom or ion
Return to ChemBits
General Chemistry Index.
All information on this page is produced by Jeffrey
Bodwin,
Copper Sun Creations, or curated from the attributed source.
This work is licensed under a Creative
Commons Attribution-NonCommercial-ShareAlike 4.0 International License.