Ions If the number of protons in an atom changes, it becomes an atom of a different element. This only happens by nuclear reaction. If the number of neutrons changes, the atom does not become a different element. It is an isotope. If the number of electrons changes, the atom does not become a different element. It becomes
an ion. Atoms that have lost or gained electrons have an electric charge and are called ions. Elements that have gained electrons have a negative charge and are called negative ions, or anions. Elements that have lost electrons have a positive charge and are called positive ions, or cations. They are positively charged because there are more positively charged protons in the nucleus than negatively charged electrons in the electron cloud.
Research this Design a poster or video animation to clearly explain what either ions or isotopes are. 22.3 Electronic structure of an atom
To make it easier to understand the structure of atoms and the locations of electrons, scientists use models. The models help us understand how the electrons in the atom are arranged.
Ions are atoms that have lost or gained electrons.
Fig. 4 Three different artistic impressions of the possible shapes of atoms.
One very useful model is the Bohr model. It is named after the Danish scientist Niels Bohr who first suggested it in 1912. Bohr suggested that the electron cloud is divided into areas
called energy levels or shells. Electrons have a definite amount of energy in these energy levels. As the number of electrons in an atom increases, more energy levels are added. Each new energy level has higher energy electrons. Bohr drew a circle to represent each energy level. He calculated that the lowest energy level could hold up to two electrons and that the next two energy levels could hold up to eight electrons each. The next energy levels could hold more electrons again. This model works very well for the first 20 elements on the Periodic Table.
Fig. 5 Niels Bohr: ‘The solution is not the answer but the question!’
