Understanding the Periodic Table of Elements

All of the numbers, letters, and colors of the Periodic Table of Elements can seem a bit overwhelming. This is a guide designed to alleviate the confusion that many of us have about chemistry's most useful tool. Let's begin.

1. A copy of the Periodic Table of Elements with a color coordinated legend.

2. You will need a computer with internet access if you do not own a copy.

3. Your brain (very important)

You may come across a periodic table that has no color or legend such as the one above. DO NOT use a periodic table like this one, it does not have the information that we will need to learn the basics.

Now that you have selected a useful table, notice the different sections that are distinguished by color. These are the categories of elements such as metals and nonmetals. Notice also that each block has unique numbers and letters to identify the elements.

The legend is a straight forward tool designed to help you easily identify what category an element is classified as based on its color within your periodic table. In the legend above, if an element is shaded purple, that element is a nonmetal and so on.

Each element within the periodic table has its own block. Within these blocks are identifying numbers and letters. The number on the very top is called the atomic number and it represents the number of protons in a single atom of the element. For the element helium (shown above) the atomic number is two. The letters in each block represent the atomic symbol. This is essentially an abbreviation of the elements name. The atomic symbol for helium (shown above) is He. Lastly, the number in the bottom of each block is an elements atomic mass number. This number represents the average weight of a single atom of the element including protons and neutrons. In the case of helium, the atomic mass number is 4.00.

Notice that each vertical column of the periodic table above is marked by a set of identifiers (1A, 2A, 3B, 4B ect...). These are known as groups. The elements are arranged in these vertical groups because they share similar properties with each other.

The elements are also arranged horizontally in rows called periods (Shown above periods 1-7). The elements in each period are not placed there at random. Much like elements in a group, elements in a particular period all share similar properties.

You may have noticed that the periodic table is also arranged in order of increasing atomic number. Hydrogen (H) is the first element with an atomic number of 1. Beginning with hydrogen in the top left of the table, atomic numbers increase from left to right and top to bottom. However, this ordering is not indicative of the size of the elements.

Atomic radius is ordered beginning in the top right of the table with helium (He) being the smallest element. Size increases on the table from right to left and top to bottom with the element in the bottom left of the table (francium of Fr) being the largest of all the elements.

1. What is the atomic number of N (nitrogen)?

2. What is the atomic mass of Na?

3. List two elements in group 8A.

4. List two elements in period 2.

5. Arrange the following elements in order of increasing atomic radius (smallest to largest). Cl, O, C.