Problem 14 - Chemistry and Chemical Reactivity

Question

Which of the first 10 elements in the periodic table are found as free elements in the Earth's crust? Which elements in this group occur in the Earth's crust only as part of a chemical compound?

Step-by-Step Solution

Answer

Nitrogen (N) and oxygen (O) are free elements. Hydrogen (H), helium (He), lithium (Li), beryllium (Be), boron (B), fluorine (F), and neon (Ne) occur in compounds.

Step 1: Identify the First 10 Elements

The first 10 elements in the periodic table are hydrogen (H), helium (He), lithium (Li), beryllium (Be), boron (B), carbon (C), nitrogen (N), oxygen (O), fluorine (F), and neon (Ne).

Step 2: Classify Elements Found as Free Elements

Free elements are found in their elemental form naturally. Among the first 10 elements, nitrogen (N) and oxygen (O) are the most common free elements found in the Earth's atmosphere.

Step 3: Classify Elements Found as Part of Compounds

Elements that are always found in compounds in the Earth's crust include hydrogen (H), helium (He), lithium (Li), beryllium (Be), boron (B), fluorine (F), and neon (Ne). Neon and helium are noble gases that are present in trace amounts in the atmosphere but not the Earth's crust as free elements.

Key Concepts

Free Elements

Free elements are atoms that are naturally found in their uncombined, pure state in nature. This means they are not bound to other elements to form compounds. In the Earth's atmosphere, two notable free elements from the first 10 elements of the periodic table are nitrogen (N) and oxygen (O).
These elements exist in molecular form, such as \( N_2\) for nitrogen and \( O_2\) for oxygen.

• Nitrogen makes up about 78% of the Earth's atmosphere.
• Oxygen constitutes approximately 21% of the atmosphere.

These elements are crucial for life processes, such as respiration and photosynthesis.
The ability of these elements to exist as free entities in the atmosphere makes them stand out among the first 10 elements of the periodic table.

Chemical Compounds

Chemical compounds are substances formed when two or more elements chemically bond together. In the Earth's crust, many elements are not found as free entities but as part of compounds.
Among the first 10 elements, hydrogen (H), lithium (Li), beryllium (Be), boron (B), and fluorine (F) are typically found in compounds when they are part of the Earth's crust.

• Hydrogen is commonly found in water (H₂O).
• Lithium is often found in minerals like spodumene.
• Beryllium is usually part of beryl minerals.
• Boron is often found in borax or boric acid.
• Fluorine commonly occurs in minerals such as fluorite.

These elements tend to combine with others to achieve more stable electron configurations, hence usually appearing as compounds.

Earth's Crust

The Earth's crust is the outermost layer of our planet. It is composed of a variety of elements and compounds that form minerals and rocks.
From the first 10 elements of the periodic table, several are more prevalent in certain forms within the crust.

• Oxygen is the most abundant element in the crust, frequently combining with other elements to form silicates and oxides.
• Aluminum, while not in the first 10 elements, is a significant component of the crust found mostly in the compound alumina.

Although elements like neon and helium are present in the Earth's atmosphere, they do not form a significant part of the crust as free elements due to their inert nature.
Understanding the distribution of these elements helps us to comprehend the composition and chemical reactions that take place within the crust and overall geologic processes.