Atoms, Ions, & Isotopes:

A short review and webquest

SWBIC Educational Resources  >> Activities & Materials  >> Atoms, Ions, & Isotopes


An Atom is the smallest recognizable part of an element containing protons (positively charged particles), neutrons (neutral particales), and electrons (negatively charged particales). Atoms are electrically neutral because they are composed of an equal number of protons and electrons.

Periodic Table – an interactive chart of the elements.
Table of Atomic Electronegativity – a periodic table with electronegativities given for each element.
Electronegativity and Bonding – an article describing the relationship between electronegativity and bond characteristics.
Valence electrons and Bonding – the relationship between valence electrons and chemical formula.


An ion is an atom that has gained or lost electrons. In non-nuclear chemistry an atom never gains or loses a proton; only the number of electrons is affected.

The following shows how a hydrogen ion is formed. The image on the left is a hydrogen atom; therefore containing an equal number of protons and electrons. The atom on the left has lost its electron; it is now an ion, and not an atom, because there is no longer an equal number of protons and electrons. The result is a charge imbalance known as a hydrogen ion. (H+)

Now let’s look at how a positive ion of beryllium is formed. Below, on the left, is a neutral atom of beryllium containing four protons and five neutrons. Circling the nucleus are four electrons. On the right, the atom has lost two electrons. The resulting ion still has four protons in the nucleus but contains only two electrons. There are now two more positive than negative charges, therefore the ion has an overall charge of 2+.

A negative ion is formed in a similar way. Below, on the left, is a image of a neutral fluorine atom containing nine protons, nine electrons, and ten neutrons. When fluorine enters into a compound, it picks up an electron from the atom it bonds with. The resulting ion, called a fluoride ion, contains ten electrons and nine protons, with an overall charge of 1-.

Ions in the Sodium-Potassium Pump – how the interplay of these ions control the movement of muscles.

Ions and your taste buds – how ions regulate taste.


Isotopes are atoms of the same element that contain different numbers of neutrons and thus have different masses. Below are drawings of the three naturally occurring isotopes of hydrogen; note that they differ only in the number of neutrons contained in their nucleus. The isotope in Fig. 1 contains only one particle in its nucleus: this isotope has a mass of one unit and is known as normal hydrogen. Fig. 2 shows a rare isotope of hydrogen. Its nucleus contains two particles (a proton and a neutron) and has a mass of two units. It is known as heavy hydrogen. Figure 3 depicts an isotope known as heavy-heavy hydrogen. The nucleus contains three particles (one proton and two neutrons) and has an overall mass of three units.

What is radioactivity? – a basic primer on the consequence of isotopes.
Use of isotopes in the Hershey-Chase experiment – how Hershey and Chase used isotopes in their famous experiment.
Medical uses of isotopes – different ways in which isotopes are used in the medical field.
Industrial uses of isotopes – several industrial uses of isotopes.
Isotopes in scientific research – how one scientist uses isotopes in her research.

Sample Review Questions

Developed for SWBIC by John Palmer, Gadsden High School.