Question

Use the periodic table to predict an ionic charge for each of the following metal ions: (a) Li ion (b) Sr ion (c) Al ion (d) \(\mathrm{Pb}\) ion

Short answer

Li: +1, Sr: +2, Al: +3, Pb: +2 or +4.

Step-by-step solution

Understanding Ionic Charge and Group Number

In the periodic table, elements are arranged in groups based on their valence electrons. Metals tend to lose electrons to form positive ions (cations) with a charge equal to the number of electrons lost, which corresponds to their group number.

Determine the Charge for Li Ion

Lithium (Li) is in Group 1 of the periodic table. Elements in Group 1 have 1 valence electron and they tend to lose this electron to achieve a stable electron configuration. Thus, the ionic charge for a lithium ion is +1.

Determine the Charge for Sr Ion

Strontium (Sr) is in Group 2 of the periodic table. Elements in Group 2 have 2 valence electrons and they tend to lose these 2 electrons. Thus, the ionic charge for a strontium ion is +2.

Determine the Charge for Al Ion

Aluminum (Al) is in Group 13 (also known as Group 3 when considering just the s and p blocks) of the periodic table. It has 3 valence electrons and tends to lose them to achieve stability. Thus, the ionic charge for an aluminum ion is +3.

Determine the Charge for Pb Ion

Lead (Pb) is in Group 14. However, unlike the other elements, lead can form multiple ions. The most common ionic charges for lead are +2 and +4 due to its ability to lose either 2 or 4 electrons.

Key concepts

Periodic Table

The periodic table is a powerful tool in chemistry, organizing elements in a structured manner based on their atomic number and properties. Each element in the table represents a building block of matter and is grouped into columns known as "groups," each possessing similar chemical behaviors.
This arrangement helps in predicting how elements interact and form compounds. Metals, primarily located on the left side of the periodic table, have a tendency to lose electrons, resulting in the formation of positively charged ions, or cations. This tendency is strongly related to their position in a specific group, which contributes to understanding ionic charges.

• Group 1 elements, such as Lithium (Li), are known as alkali metals and are highly reactive.
• Group 2 elements, such as Strontium (Sr), are known as alkaline earth metals and also form cations easily by losing electrons.
• Group 13 elements, like Aluminum (Al), are recognized for typically losing three electrons to form cations.

The placement of an element in the periodic table gives a glimpse into its behavior during chemical reactions.

Valence Electrons

Valence electrons are crucial as they determine how an element will react and form bonds with other elements. These electrons reside in the outermost shell of an atom, and their number can be predicted based on the element's group number in the periodic table.
For metals, losing these outer electrons results in the formation of cations. Each loss of an electron results in a positive charge, and metals do this to achieve a stable electron configuration popularly known as the noble gas configuration.

• Each element in Group 1 has one valence electron and tends to lose it, forming a +1 cation.
• Group 2 metals have two valence electrons and typically form +2 cations by losing both.
• For elements in Group 13, like Aluminum (Al), all three valence electrons are lost, resulting in a versatile cationic charge of +3.

Understanding valence electrons helps predict the behavior of metals in reactions and their ionic charges, contributing significantly to understanding chemistry.

Cations

Cations are ions with a positive charge formed when an atom loses one or more electrons. The loss of negatively charged electrons results in a net positive charge.
For metals, which are the primary cation formers, this process is central to their chemical identity. The specific positive charge a metal cation carries depends on the number of electrons it loses during ionization, heavily related to its position in the periodic table.

• Lithium (Li), a Group 1 metal, becomes a +1 cation since it loses one valence electron.
• Strontium (Sr), a Group 2 metal, forms a +2 cation by losing two electrons.
• Aluminum (Al) typically loses three electrons to form a +3 cation.
• Lead (Pb), however, is more complex, capable of forming +2 or +4 cations due to options in losing either two or four electrons, an exception driven by the weak ability to hold onto its outer electrons.

Analyzing cations helps in understanding the electrical and chemical properties of metals and their compounds in various chemical contexts.