Chemistry of Some Common Substances
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 about chemistry.
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 sodium hydroxide.
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.
Metals
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 metals
Pewter: mixture of tin, copper, bismuth, and antimony
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.
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