Component 1: Short Review
Q1:
Name a common compound that is used every day.
Water (H₂O)
- Almost no living thing can survive without water. It’s essential for life on Earth. A water molecule consists of one oxygen atom combined with two hydrogen atoms1.
Q2:
If elements and compounds are both pure substances, then what is the difference between
them?
Here are the differences between elements and compounds:
1.) Elements:
- Elements are fundamental substances that cannot be broken down into simpler substances by chemical means.
- Each element consists of only one type of atom. For example, oxygen (O), hydrogen (H), and carbon (C) are elements.
- Elements are listed in the periodic table, and they have unique atomic numbers.
- They can exist as individual atoms (e.g., oxygen gas, O₂) or in combined forms (e.g., carbon dioxide, CO₂).
2.) Compounds:
- Compounds are pure substances composed of two or more different elements chemically bonded together.
- They have fixed ratios of elements. For instance, water (H₂O) always contains two hydrogen atoms and one oxygen atom.
- Compounds exhibit distinct properties different from their constituent elements.
- Examples include table salt (NaCl), glucose (C₆H₁₂O₆), and ammonia (NH₃).
In short, elements are the building blocks of matter, while compounds result from the combination of elements.
Q3.
Why are compounds considered to be pure substances?
Compounds are considered pure substances due to their consistent composition and fixed ratios of elements. Here are the reasons why:
- Fixed Composition => Compounds have a specific arrangement of atoms. For example, water (H₂O) always contains two hydrogen atoms and one oxygen atom. This consistent composition distinguishes compounds from mixtures.
- Chemical Bonding => Compounds result from chemical bonding between different elements. These bonds are strong and stable, ensuring that the compound maintains its identity.
- Distinct Properties => Compounds exhibit unique properties different from their constituent elements. For instance, sodium (Na) is a reactive metal, while chlorine (Cl) is a toxic gas. However, when combined as sodium chloride (NaCl), they form table salt, which is safe for consumption.
In summary, compounds are pure substances because their composition remains constant, and they exhibit specific properties.
