Give the full symbol for the atom or ion that has eight protons and eight neutrons in its nucleus and ten electrons outside its nucleus. Also give the name of the group this element is in.

The atomic number is one of the most fundamental concepts in chemistry as it defines the identity of an element. It represents the total number of protons within the nucleus of an atom. Since each element has a unique number of protons, the atomic number is set and cannot change; altering the number of protons transforms the atom into a different element entirely.

For example, when we say an atom has an atomic number of 8, as in the exercise provided, we are referring to the element oxygen. This is because, on the periodic table, oxygen is the element that is assigned the atomic number 8. The atomic number is usually noted at the top of the element's square on the periodic table and is critical in determining the placement of the element within different groups and periods of the table.

The charge of an ion is determined by the difference between the number of protons (positively charged) and electrons (negatively charged) within an atom. When an atom gains or loses electrons, it becomes an ion; gaining electrons results in a negative charge, while losing electrons results in a positive charge.

The number next to the plus or minus sign indicates the magnitude of the charge. In the exercise, the oxygen atom has gained two electrons more than protons, giving it a net charge of -2, which is indicated in the ion symbol as ewline O^{2-}. This is an important concept to understand as it affects the atom's reactivity and the type of chemical bonds it can form.

Organization by Similar Properties

Groups in the periodic table are the vertical columns that organize the elements according to their similar properties and the number of electrons in their outer shell. Group numbers run from 1 to 18, and they are key to predicting the chemical behavior of the elements within them.

Elements in the same group typically have similar reactions to other substances due to having the same number of electrons available for bonding, which is known as the valence electrons. These shared characteristics simplify understanding chemical reactions and the trends seen as you move up or down a group in the periodic table.

The chalcogen group, also known as group 16, includes elements like oxygen, sulfur, and selenium. These elements are known for their ability to form compounds by gaining two electrons, as seen with the oxygen ion in our exercise example. This property results in the formation of a -2 ion. Chalcogens play a crucial role in various biochemical and industrial processes.

Members of this group are found in a wide variety of compounds ranging from oxides and sulfides to various organic compounds. Oxygen, the first element in this group, is vital for life as it is a primary component of a variety of life processes, including cellular respiration.