Lecture 12: Chemistry Chapter 1 p. 8-18

1. All matter is composed of elements (basic substances).

92 elements are found in nature

a. Symbols of 1 or 2 letters are assigned for every element (Periodic Table)

 HONC if you love chemistry

96% of living matter is made of the above 4 elements (table 1.3 in Levetin)

H=hydrogen

O=oxygen

N=nitrogen

C=carbon

b. The smallest part of an element having all the properties of that element is called an atom.

c. Atoms are made of 3 sub-atomic particles, protons, neutrons and electrons

d. Where are the 3 sub-atomic particles located? Fig. 1.5

• Nucleus: contains protons and neutrons
• Orbital shell contains electrons

A small nucleus in the middle contains all the weight of the atom while electrons move around on the outside. As an analogy, if an atom was a football stadium, the nucleus would be a baseball at the 50 yard line weighing several million tons. Flies flitting about in the stands represent the electrons. Most of an atom is empty space!

2. Molecules

More than one atom linked together is a molecule.  Atoms are joined together by chemical bonds.

3. Compounds

A molecule built with more than one kind of atom is a compound.

Look at the following list. See if each formula is a) atom or molecule or b) element or compound.

4. Chemical reaction

Atoms join to form molecules, or molecules have their bonds broken and rearranged to form new molecules. Example:

Na=sodium=an explosive metal

Cl=chlorine=a poisonous gas

NaCl=sodium chloride=common table salt, edible and non-reactive

The new molecules have different chemical and physical properties than the original atoms or molecules.

5. Physical vs. Chemical changes

Physical changes: Water can be solid, liquid or gas but it is still water, H₂O

Chemical changes: A molecule rearranges atoms and combines with other atoms. A reactive molecule rearranges easily. Gasoline is an example of a reactive compound. A non-reactive molecule does not easily react. For example, even at high temperatures, glass changes to a liquid but still remains glass.

Cellular respiration is an example of a chemical reaction:

Cells get energy by combining glucose with oxygen and rearranging the atoms into carbon dioxide and water.

Label each substance below.

C₆H₁₂O₆ +  O₂-->CO₂ + H₂O

___________________  + ______________-->_________________+__________________

Since the principle of conservation of mass states that molecules are never gained or lost but simply re-arranged, we must balance this equation so the same number of carbon, hydrogen and oxygen atoms are found on both sides

C₆H₁₂O₆ +  ___O₂ --> 6 CO₂ + ___H₂O

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