Chemistry of Some Common Substances
There will probably be several questions on the SAT II
exam that will ask about some common properties of chemicals. The
list below constitutes some of the things that everyone should know
Group 1A (Alkali Metals)
This group consists of the most active metals on the periodic
table; these metals react with water at room temperature to form
bases. They react readily with acids to produce hydrogen gas and
get even more reactive as you move down the family. This makes sense
because as you move down the family, there are more energy levels,
more shielding, so it’s harder for the nucleus to hold on to the
lonely valence electron, and so on. Many drain cleaners contain
Group 7A (Halogens)
This group contains the most reactive nonmetals on the
periodic table, and all of these elements are diatomic. Fluorine
is a gas, bromine is a liquid, and iodine is a solid, which makes sense
because as the molecules get larger, there are more intermolecular
forces to hold them together. Fluorine is the most reactive of the
halogens. Chlorine is a very common antibacterial agent, found in
bleach and muriatic acid (HCl), and is added to every city’s water supply.
Fluorine is the anti-tooth-decay element. Most cities also add fluoride
ion to the water supply.
Group 8A (Noble Gases)
The noble gases are considered the most stable family
on the periodic table. Many of these gases appear in signs (such
as neon signs). Helium is used to fill balloons because it is much less
dense than air. Argon is fairly abundant in our atmosphere.
You might recall from our earlier discussions (see “The
Structure of Matter”) that metals have a positive center surrounded
by a sea of electrons. This sea of electrons makes metallic substances
very good conductors of electricity. Alloys are
substances that contain a mixture of elements that have metallic
properties. An alloy is often much stronger than the individual
metal itself. Some of the more common alloys include
Brass: mixture of copper and zinc
Sterling silver: mixture of silver and copper
Steel: mixture of iron and carbon
Bronze: mixture of copper, zinc, and other
Pewter: mixture of tin, copper, bismuth,
Properties of Some Common Gases
Hydrogen: H2 is a
colorless, odorless gas. It was once used to fill blimps because
of its low density, but now helium is used since hydrogen is very
flammable. When hydrogen gas is collected in a test tube in the
lab, a burning splint inserted into the test tube filled with hydrogen
will “bark” as the hydrogen ignites.
Oxygen: O2 makes up
about 21% of our atmosphere (the other major gases that make up the
atmosphere are nitrogen and argon). It is a colorless, odorless
gas that is necessary for life and supports combustion reactions.
When oxygen is collected in a test tube in the laboratory, a glowing
wooden splint will reignite.
Carbon dioxide: CO2 is
also a colorless, odorless gas that does not support combustion; many
fire extinguishers use carbon dioxide to extinguish flames. When
carbon dioxide gas is collected in a test tube in the laboratory,
a burning wooden splint will go out when placed into the gas. Another
common lab test for CO2 is to bubble it into
limewater, Ca(OH)2. The clear solution will
turn cloudy as calcium carbonate, CaCO3,
begins to precipitate.
Chlorine: Cl2 is a
deadly yellow-green gas. It has often been used as a weapon in warfare.