In the diagram, an atom of sodium loses one electron from the outer shell. What is formed when this electron is lost?
An atom is electrically neutral because it contains the same number of positively charged protons and negatively charged electrons. The atom of sodium contains 11 electrons. Therefore, it must also contain 11 protons. When a sodium atom loses an electron, it forms a species with 10 electrons and 11 protons. A chemical species with an unequal number of protons and electrons is called an ion. This ion has more positively charged protons than negatively charged electrons and is therefore positively charged overall.
So, when an atom of sodium loses one electron from the outer shell, a positive sodium ion is formed.