Fundamentals of Chemistry 1030
Elements, Compounds, & Mixtures
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Elements, Compounds & Mixtures

There are 116 known elements in which 110 or more are arranged in groups and periods on the Periodic Table. Elements are the primary substance from which all other things are made. Elements can not be broken down into simpler substances.

When two or more different elements are chemically combined, they form compounds. Just about everything you see around you is made up of compounds. In a compound, each element is present in a fixed whole-number ratio. This ratio is represented by the chemical formula of a compound. For example, water has the chemical formula H2O. This tells us that each water molecule always has 2 atoms of hydrogen and 1 atom of oxygen.

When two or more substances (elements or compounds) are physically combined, they form a mixture. The components of a mixture retain their individual physical properties and they can be separated by physical means. For example, if we mix plain M&M’s with peanut M&M’s, the plain M&M’s will still be plain and the peanut will still be peanut. Furthermore, we can physically separate the two types of M&M’s and neither type will have changed from their original existence.

Properties of Elements & Compounds

Observation of a substance allows us to describe physical properties such as shape, state, color and luster. Other physical properties can be measured such as density, melting point, and boiling point. The physical properties of an element or compound are characteristics that do not change unless the element or compound undergoes a chemical change to form a new substance. Therefore, physical properties for many substances can be found in reference books such as the CRC Handbook of Chemistry and Physics.

Types of Bonding in Compounds

The elements in compounds are held together by chemical bonds. Two types of chemical bonds are ionic bonds and covalent bonds. Ionic bonds form when a metal element combines with a nonmetal element. The metal loses electrons to form a positive ion and the nonmetal gains electrons to form a negative ion. Since opposites attract, the negative and positive ions are attracted to each other to form the ionic bond. When two nonmetals form a compound, they share electrons and form covalent bonds.

Laboratory Procedures

A. Formulas of Compounds

Your instructor will show you a display of compounds and elements. Coose five of these compounds and for each compound, describe the physical properties, write the chemical formula, state the number of atoms of each element present in that compound. From the display of the elements, record some of the physical properties of the individual elements. You may want to make a table like the one below. Make the table large enough for at least five compounds. Note:  Each compound could have as many as 5 different elements, so leave leave plenty of room in your chart for each compound.

Table 1. Interpreting Formulas of Compounds
 
 
Compound
Formula of Compound
Physical Properties of Compound
Number of Atoms of each Element
Physical Properties of the Elements
1.
water
H2O
colorless liquid
2 H, 1 O
H - colorless gas 
O-colorless gas
2.
 
       

 
 

B. Physical Properties of Iron sulfide and Its Elements

1. Obtain samples of iron (Fe), sulfur (S), a mixture of iron and sulfur (Fe + S), and iron(II) sulfide (FeS). Describe the observable physical properties of each sample in Table 2 (color, state, luster).

2. Using a chemistry handbook (CRC), look up the density, melting point, and boiling point of Fe, S, and FeS. Record these in Table 2.

Table 2. Physical Properties Data
 
Sample
Observable Physical Properties
Density
Melting Point
Boiling Point
Fe
       
S
       
Fe + S
 
----
----
----
FeS
       
3. Test each sample for magnetic attraction by running a bar magnet under each sample. (Do not place the magnet directly into the samples.) If there is magnetic attraction, the particles will follow the magnet. Record your observations in Table 3.

4. Describe each sample as a metal or a nonmetal in Table 3. (Metals will be attracted to the magnet and nonmetals will not be attracted to the magnet.)

5. Describe each sample as an element, mixture, or compound in Table 3.

Table 3. Elements, Compound & Mixtures
 
Sample
Magnetic Attraction
Metal or Nonmetal
Element, Compound or Mixture
Fe
     
S
     
Fe + S
     
FeS
     
Issues to be addressed in your conclusion...

Why do the physical properties of iron and sulfur differ from those of iron(II) sulfide?

Could the elements in the Fe + S mixture and the compound FeS be separated using the same methods? Why or why not?

How does the magnetic attraction differ for the elements, mixture, and compound?

Explain the following statement in your own words: In a compound, there is a definite composition of the elements.

(updated 1-19-07  P Powers)