Families and the Type of Ion Formed

As we have seen in this section, elements in the same groups are related to each other by their electron configurations. Since the families of elements were organized by their chemical behavior, it is predictable that the individual members of each chemical family will have similar electron configurations. Because of the similar electron configuration, elements in the same group have similar properties. One important characteristic to know for each group (family) is the type of ion formed by the elements. This information will be used over and over again throughout the rest of this course.

As we discussed earlier an ion is a charged atom. The atom acquires a charge when it loses or gains electrons. There are two types of ions: cations and anions. A cation ion is a positive ion in which electrons have been lost. Remember, since electrons are negative when you lose or get rid of them you end up having more protons which give the overall charge positive. An anion is a negative ion in which electrons have been gained. Again, since electrons are negative having more of them means that the overall charge is negative. Metals have a tendency to lose electrons resulting in cations, whereas nonmetals have a tendency to gain electrons resulting in anions. Here is a picture to help you visualize the difference between a cation and an anion:

Type Of Ion Formed:
Cation Formation
Taking electron from Sodium
Anion Formation: adding electron to Flourine

Because the elements in the main groups of the periodic table (groups 1-2, groups 13 - 18) have the same number of valence electrons, they form the same type of ion. Let's look at the main groups.

All metals of the Group 1 family (Alkali Metals Family) will tend to lose only one electron when ionized. This is because all of the elements in Group 1 have just 1 valence electron. When they lose this 1 valence electron, then they have a full outermost energy level and are stable. The entire family forms +1 ions: Li⁺¹, Na⁺¹, K^+1, , Rb⁺¹, Cs⁺¹, and Fr⁺¹. Note that although hydrogen (H) is in this same column, it is not considered to be a metal. There are times when hydrogen acts like a metal and forms +1 ions, but most of the time it bonds with other atoms as a nonmetal. In other words, hydrogen doesn't easily fit into any chemical family.

All metals of the Group 2 family (Alkaline Earth Metals Family) will tend to lose two electrons when ionized. This is because all of the elements in Group 2 have just 2 valence electrons. When they lose the 2 valence electrons, then they have a full outermost energy level and are stable. The entire family forms +2 ions: Be⁺², Mg⁺², Ca^+2, , Sr⁺², Ba⁺², and Ra⁺².

Most of the elements in Group 16 are nonmetals and will tend to gain two electrons when ionized. This is because all of the elements in Group 16 have 6 valence electrons. It is easier to gain 2 electrons than it would be to try to lose 6 electrons. When they gain the 2 valence electrons, then they have a full outermost energy level and are stable. The entire family forms -2 ions: O^-2, S^-2, Se^-2, , and Te^-2.

The elements in Group 17 are nonmetals and will tend to gain one electron when ionized. This is because all of the elements in Group 17 have 7 valence electrons. It is easier to gain 1 electron than it would be to try to lose 7 electrons. When they gain 1 valence electron, then they have a full outermost energy level and are stable. The entire family forms -1 ions: F^-1, Cl^-1, Br^-1, , and I^-1.

The elements in Group 18 are nonmetals but since they all have 8 valence electrons, they are stable and do not want to gain or lose electrons.

Look at the picture below for a summary of the text above:

periodic table with the transition metals form cations with various charges notated

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