The periodic table lists the elements
in order of increasing atomic number. Each element is described by its name,
atomic weight, atomic symbol, and atomic number. Elements with similar
characteristics are listed in vertical groups called families.
Elements are composed of small
particles called atoms. Atoms are the smallest units of an element that can
combine with other elements. Atoms of different elements combine to form
compounds. Baking soda (sodium bicarbonate),
for example, is made of sodium, hydrogen, carbon, and oxygen. Hydrogen gas,
composed of two hydrogen atoms is technically a compound. The chemical
formula of a compound lists all the elements that make up the compound and
their proportions. The smallest unit of a compound is a molecule.
A physical property of an element or
compound is any characteristic that can be observed such as color, odor,
density, hardness, or melting point. A chemical property refers to the
chemical composition of that substance. For example, silicon (Si) and oxygen
(O) make up quartz, silicon dioxide (SiO2). A physical change
occurs when a compound changes state, for example, ice melting to form
water. No new elements or compounds are formed. Physical changes require no
modification of the internal molecular arrangement of the compound.
A chemical change occurs when a new compound is
produced as a result of a reaction between two substances. Chemical changes
cause permanent changes in the composition of the material, for example wood
changes composition when burned to ash.
- Review the Periodic Table with the students. Ask them to find elements
that are used in daily language. For instance: ______ Valley (Silicon);
_____ makes strong bones (calcium); _____ helps fight a sore throat
(zinc); a coin is named after this element (nickel). See if the students
can come up with more examples. This will help you determine the level
of your student’s knowledge of the elements.
- Ask your students to determine whether each of the following is a
chemical or physical change. You may want to demonstrate some of these
changes before the students respond.
- bending a toothpick (physical)
- burning a match (chemical)
- burning sugar (chemical)
- making a cake from scratch (chemical)
- smashing a can (physical)
- making instant coffee (physical)
- melting ice to water (physical)
- Scientists use
the atomic symbols of the elements to help record chemical reactions,
because it is easy to write the reaction in this chemical "short
hand." Go through the chemical reactions below with your students.
You may want to have them use the Periodic Table to locate the symbols.
Don't worry about the numbers in the equations.
H2 + Cl2 ---------> 2 HCl
hydrogen (a gas) + chlorine (a gas) yields 2 molecules of hydrochloric
CuO + H ---------> Cu + H2O
copper oxide + hydrogen (a gas) yields copper + water
H2 + S ---------> H2S
hydrogen (a gas) + sulfur yields hydrogen sulfide