What Demonstrates That a Solid Sample Is a Compound?
In 1807, English scientist John Dalton proposed the first definition for what he called a "chemical compound." Compounds, he theorized, were combinations of more than one element in specific, well-defined proportions. Scientists call a substance a compound if it meets certain criteria --- essentially the same criteria defined by Dalton, only modern science has many more tools to study molecules than were available in Dalton's day and age.
Other People Are Reading
-
Pure Substance
-
A compound is a pure substance, not a mixture. Table salt, for example, would not be called a compound because it's actually a mixture of several compounds --- salt, dextrose, calcium silicate and potassium iodide. Scientists can analyze mixtures and solid samples through a wide variety of techniques including chromatography, infrared spectroscopy and chemical tests. If a scientist found that a solid sample contained one type of substance only and no others, that sample could be described as a pure compound.
Multiple Elements
-
By definition, a compound contains more than one element. Diamond and graphite are not compounds because they consist solely of carbon. Sucrose sugar, by contrast, contains carbon, oxygen and hydrogen, so it would meet the criteria to be defined as an element. A scientist can determine the chemical formula of a pure sample through tests such as combustion analysis or mass spectrometry; so if only one element is present, you can conclude the solid sample was not a compound.
-
Definite Ratio
-
A compound contains elements in a definite ratio, meaning the proportion of those elements with respect to each other is fixed and does not change. If a scientist found that some pieces of a solid sample were 50 percent sodium by weight while other pieces were 10 percent sodium by weight, then you could conclude the sample is not a compound; this is because the elements it contains are not present in a well-defined ratio.
Chemistry
-
A mixture is formed by a physical change, while a compound is formed through a chemical reaction. Consequently, the compound is chemically distinct from the elements that make it up and will have different properties. Think about sodium chloride, for instance. Sodium is a metal so soft you can slice it with a butter knife; it reacts explosively with water. Chlorine is a poisonous gas that reacts violently with hydrogen. Combine the two and you get sodium chloride, a compound so safe you can sprinkle it on your food --- something you could never do with either of the two elements in it.
-
References
- Photo Credit Photos.com/Photos.com/Getty Images
