Web Activity 2.2, 2.4 - Distinguishing Elements, Compounds & Mixtures

The simplest kind of matter is an element. The smallest unit of an element that acts like that element is called an atom.

Ancient alchemists used more than one symbol for each element. For a time, the astronomical symbols of the planets were used to denote the elements. However, as alchemists came to be persecuted, particularly in medieval times, secret symbols were invented. This led to a great deal of confusion, so you will find some overlap of symbols. Now chemists use universal chemical symbols to represent each element.

Each of the following test tubes contains an element. For fun, an example of the alchemical symbol has been given in addition to its modern chemical symbol. Go to WebElements.com or click the symbol or test tube to identify the element and find 3-4 physical properties for each.

1. element name: ______________ physical properties:

2. element name: ______________ physical properties:

3. element name: ______________ physical properties:

4. element name: ______________ physical properties

The following substances are minerals or compounds occurring in nature. Chemists represent compounds by chemical formulas. The smallest unit of a compound that acts like that compound is called a molecule. Go to http://mineral.galleries.com or click on each picture to find the chemical formula and 3-4 physical properties for each.

5. pyrite (iron sulfide) - formula: ______________ physical properties:

6. cinnabar (mercury sulfide) - formula: ______________ physical properties:

7. stibnite (antimony sulfide) - formula: ______________ physical properties:

8. From the formulas alone, what can you say about the composition of each of the three compounds above?

9. From the physical properties alone, could you have determined the identity of the elements that are combined to make up these compounds? Explain.

10. What general statement can you make about the properties of elements when they combine to form compounds?

11. Make an attempt to explain the numerical subscripts in one of the compound’s chemical formula.

If you stir together some iron filings and sulfur, you have made a mixture.

12. Do you have to measure to make a mixture?

13. How could you remove the iron from this mixture? Could you use the same technique to separate iron and sulfur in the compound iron sulfide (pyrite)? Explain.

14. How would the properties of a mixture of iron and sulfur compare to those of the compound of iron and sulfur (iron sulfide – pyrite)?

15. Pure substances have uniform properties throughout and a definite composition from sample to sample. Of elements, compounds and mixtures, which are pure substances?