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| Unit 3: Active Chemistry |
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When elements combine they form new substances called compounds. These compounds have entirely new characteristics. It is like combining the letters of the alphabet to make words. Twenty-six letters can be combined to make thousands of different words.
Water is an example of a compound. A water molecule, H2O, is composed of two atoms of hydrogen and one atom of oxygen. (For now, think of an atom as the smallest particle of an element and a molecule as the smallest unit of a compound.) In this activity you used electricity to decompose water into its elements, hydrogen and oxygen. This process is called electrolysis. You observed that oxygen gas made a glowing splint burst into flame, and that hydrogen gas was explosive. However, to extinguish a burning splint, you could use liquid water. The compound has very different characteristics from the elements from which it is made.
Compounds are represented by chemical formulas. A chemical formula shows the symbols of the elements that are combined to make the compound. If there is more than one atom of an element, a subscript is added after the symbol indicating how many atoms of that element there are. For example, as you discovered in this activity, the chemical formula for water is H2O. |
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| Compound |
Common Name |
Chemical Formula |
| calcium carbonate |
chalk |
CaCO3 |
| carbon dioxide |
dry ice |
CO2 |
| hydrochloric acid |
muriatic acid |
HCl |
| hydrogen sulfide |
rotten-egg gas |
H2S |
sodium hydrogen carbonate
(or sodium bicarbonate) |
baking soda |
NaHCO3 |
| sodium chloride |
table salt |
NaCl |
| sodium nitrate |
fertilizer |
NaNO3 |
| sulfuric acid |
battery acid |
H2SO4 |
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Chem Words
compound: a material that consists of two or more elements united together in definite proportion. electrolysis: the conduction of electricity through a solution that contains ions or through a molten ionic compound that will induce chemical change. chemical formula: the combination of the symbols of the elements in a definite numerical proportion used to represent molecules, compounds, radicals, ions, etc.
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Activity Page 6 
