All atoms by their nature are electrically neutral, meaning they have equal numbers of protons and electrons. The protons carry a positive charge and the electrons carry a negative charge. Because electrons are weakly bound to atoms, however, the passage of other nearby atoms can strip them away. An atom that loses or gains electrons in this fashion is called an ion. An atom with more electrons that protons is referred to as a negative ion, while those with more protons are identified as positive ions. These charged atoms are responsible for many processes, such as electrical current and chemical reactions.
Students learning about charged atoms are unable to visually observe these processes in real life because of the infinitesimal size of the objects. This makes it very beneficial to utilize model making activities. Tactile students especially benefit from hands-on learning, such as making the traditional foam ball and toothpick models. In these, it helps to use smaller balls to represent electrons to reinforce the idea of the relatively smaller size of these particles. Depending on the age and maturity of the students, however, you can utilize many different media for models including fruit, modeling clay, pen and paper or even computer software.
Because of the ease of removing electrons from a surface using friction, activities using charged items are simple to set up. Common items such as combs and balloons are easy to "charge" simply by rubbing them with cloth. Students are often amazed at the capability of the surface of a balloon or a comb to cause tiny strips of paper to levitate and adhere to them. Another intriguing experiment is to use a comb to bend a stream of flowing water. A small trickle can be deviated several inches, seemingly flowing around a corner because of the influence of charged atoms.
Because water is a universal solvent, it can break down almost any simple chemical compound (such as salt, vinegar or baking soda) into ions. The proportion of charged hydrogen atoms in water creates a measurable feature that scientists refer to as pH. You can create informative activities where students observe how adding different household chemicals to water changes the amount of free hydrogen in solution. Students will require a tool to measure pH such as litmus strips or chemical indicators. Since red cabbage juice is a natural indicator, it can be utilized as an interesting extension to the activity.