Lecture 2: Chemistry and Geology Refresher
1. The Atom
means "indivisible" in ancient Greek (a=not, tomos=divided). The concept of atoms
and elements are closely linked. An element cannot be broken down into simpler substances
by ordinary chemical or physical means. Rust, iron oxide, can be broken down into iron and
oxygen, but iron cannot be broken down into anything simpler. An atom is the smallest
particle that retains all of the properties of an element. Atoms combine (bond) together to
form compounds. Most minerals (and gems) are chemical compounds. The chemical and
physical properties of minerals is tied to the atoms within their structure.
is at the center of the atom, where most of the mass of an atom lies.
lie within the nucleus (by convention, protons and neutrons each have a mass
of 1). A proton has an electrical charge of +1, while a neutron (as the name indicates) has no
charge. The electrical charge of protons is additive so that two protons have an electric
charge of +2, four protons have a charge of +4,
Surrounding the nucleus is a cloud of
. An electron has negligible mass compared
to the nucleus, but it has a charge of -1 (exactly opposite of a proton). In normal atoms, the
number of protons and electrons is the same: the net electric charge of an atom is zero.
In 1912, Danish physicist Niels Bohr proposed an atomic model where each electron orbited
a set distance from the nucleus. Instructors often use this model as an introduction students
to the atom - understanding chemical reactions and atomic bonds is relatively
straightforward and simple to represent graphically, but it doesn't work for anything more
than that. Modern models of the atom place electrons in a region of probability - a place
where they are most likely to be found. This is represented by fuzzy clouds surrounding the
nucleus. This is more accurate, but it can be harder for the non-scientist to grasp. For this
class we will think of atoms (and their constituent particles) as solid spheres of varying
sizes. This allows us to think of atoms as small building units of larger structures and see the
difference between atoms.
The periodic table is, stated simply, a list of all the different kinds of atoms there are.
Elements are merely these atoms, each with it's own chemical and physical properties. Each
element has a different number of protons in the nucleus. For example, Hydrogen (element
symbol: H) has one proton in its nucleus. Helium (He) has two, Lithium (Li) has three, and
There are 92 naturally occurring elements and about another 25 that have been artificially
created in the lab. While it's not important to know all 92 elements and their abbreviations,
you will be responsible for knowing ten of the most common elements in the earth's crust
(which are often found in gems):
[O] (most common),