Show the teenagers a periodic table of the elements, telling them ALL the materials we know and use are composed of elements and their combinations with each other. Common salt for example has two elements: sodium, a solid, and chlorine, a gas. Water is made of two gases: oxygen and hydrogen. Sugar is composed of oxygen, hydrogen and carbon. Have the students think of other materials and tell them the elements that make them.
Tell the teens to use graph paper to copy a periodic table with rows and columns. There will be small squares or "boxes" to represent the elements. Have them number the columns from 1 to 18 starting from the left column.
Have the students number the boxes from left to right, starting with 1 for hydrogen, 2 for helium, 3 for lithium, 4 for beryllium, 5 for boron, 6 for carbon, 7 for nitrogen, 8 for oxygen, 9 for fluorine and 10 for argon. Let them continue until box 86 for radon
Teach the students mnemonics for remembering the order of the elements. For example, elements 5 to 10 have symbols BCNOF. A useful mnemonics would be Be Careful Now Of Foxes. Challenge them to develop their own mnemonics for rows and columns of the periodic table.
Column 2 has Be, Mg, Ca, Sr, Ba, Ra. A mnemonic could be Betty Meg Call Sister Barbara. With a little imagination, the kids can churn out other interesting mnemonics that will make memorizing the entire periodic table easy and fun. They even could convert the mnemonics into lyrics and songs.
Explain to the teens that when the elements are arranged in an orderly format, those in a column tend to have periodic properties that increase or decrease. For example, the atomic radius increases down a column of elements but tends to decrease as you move from left to right in a row.
Each of the elements has special uses. Some are found even in the human body and bones. Have the students research and present in class the usefulness of each element. Give prizes to the best three presentations. Let them also design competitive quizzes. Reward the best students and best student groups, and give consolation prizes to the others.