Problem 37 - Chemistry Matter and Change

Question

Metals What is the oxidation number of alkaline earth metals in their compounds? Of alkali metals?

Step-by-Step Solution

Answer

Alkaline earth metals in compounds have an oxidation number of +2, while alkali metals have an oxidation number of +1.

Step 1: Understanding Oxidation Numbers

An oxidation number is a positive or negative number that indicates how many electrons an atom gains, loses, or appears to use in the formation of a compound. It's crucial to start by knowing the general rules for determining oxidation numbers for different groups on the periodic table.

Step 2: Identifying Alkaline Earth Metals

Alkaline earth metals are elements found in Group 2 of the periodic table. This group includes elements like calcium (Ca), magnesium (Mg), and others. The common characteristic of these metals is that they typically lose two electrons during chemical reactions.

Step 3: Oxidation Number of Alkaline Earth Metals

Since alkaline earth metals lose two electrons, they typically have an oxidation number of +2 in their compounds. This is a fixed oxidation state due to their tendency to lose the two valence electrons to achieve a stable electron configuration.

Step 4: Identifying Alkali Metals

Alkali metals are found in Group 1 of the periodic table, including elements like sodium (Na), potassium (K), and others. These metals lose one electron to achieve a full outer electron shell.

Step 5: Oxidation Number of Alkali Metals

In compounds, alkali metals commonly have an oxidation number of +1. This is because they donate their one valence electron to complete their electron configuration, becoming positively charged.

Key Concepts

Alkaline Earth Metals

Alkaline earth metals belong to Group 2 of the periodic table. These metals include familiar elements such as calcium (Ca) and magnesium (Mg), as well as beryllium (Be), strontium (Sr), barium (Ba), and radium (Ra). One defining characteristic of these metals is their ability to lose two electrons during chemical reactions.

Due to this tendency, alkaline earth metals typically exhibit an oxidation number of +2 in their compounds. This number represents the charge of the ion after it loses two electrons to form a stable electronic configuration. This characteristic oxidation state is quite stable and does not vary much between the elements of Group 2.

Understanding this can greatly aid in predicting how these metals will behave during chemical reactions. They are known for forming ionic compounds and are highly reactive, especially with oxygen and water.

Alkali Metals

Alkali metals make up Group 1 of the periodic table and include elements such as sodium (Na), potassium (K), lithium (Li), rubidium (Rb), cesium (Cs), and francium (Fr). These metals are known for their high reactivity, even more so than alkaline earth metals. The reason for this reactivity lies in their single outer electron, which they easily lose to achieve a full electron shell.

When alkali metals lose this one electron, they form a +1 ion, hence their oxidation number is typically +1. This is a key aspect of their chemistry and results in their formation of stable ionic compounds. For example, sodium (Na) reacts with chlorine (Cl) to form sodium chloride (NaCl), a compound where sodium has an oxidation number of +1.

Given their reactivity, alkali metals must be stored under oil to prevent their reaction with moisture in the air. This high reactivity also means they are not found in their elemental form in nature.

Periodic Table Groups

The periodic table is organized into groups and periods to help us understand elements' properties and behaviors. Each group consists of elements that share similar chemical properties. For instance, Groups 1 and 2, which include alkali and alkaline earth metals, respectively, are known for their metals that tend to form cations by losing electrons.

Elements within the same group also exhibit a trend in their reactivity and oxidation states due to their similar valence electron configurations. For example, the similarity in oxidation states among alkaline earth metals (+2) and alkali metals (+1) reflects their predictable behavior in chemical reactions.

The concept of groups extends beyond just these two metals. The periodic table includes several other groups, each with unique properties and characteristic reactions. Learning these patterns and trends aids in predicting how an element might interact in a chemical process, easing the study of chemistry and identifying unknown compounds.