Question

Indicate whether each of the following statements is true or false. If a statement is false, correct the statement so that it becomes true. a. Most materials occur in nature as pure substances. b. A given compound usually contains the same relative number of atoms of its various elements. c. Atoms are made up of tiny particles called molecules.

Short answer

a. False. Corrected statement: Most materials occur in nature as mixtures. b. True. c. False. Corrected statement: Molecules are made up of tiny particles called atoms.

Step-by-step solution

a. Analyzing the statement

Most materials occur in nature as pure substances. This statement is false. Most materials in nature are mixtures, not pure substances.

Correcting the statement

Most materials occur in nature as mixtures.

b. Analyzing the statement

A given compound usually contains the same relative number of atoms of its various elements. This statement is true. Compounds have a specific ratio of elements that are combined in a fixed proportion.

c. Analyzing the statement

Atoms are made up of tiny particles called molecules. This statement is false. Atoms are not made up of molecules; instead, molecules are made up of atoms.

Correcting the statement

Molecules are made up of tiny particles called atoms.

Key concepts

Pure Substances vs Mixtures

Imagine you are walking through a forest. Most of the things you see aren't pure substances, but rather mixtures. A pure substance is something that has a definite and constant composition.
For instance, water (H₂O) is a pure substance because it always contains two hydrogen atoms and one oxygen atom.

On the other hand, mixtures are combinations of two or more substances where each retains its own properties. The air we breathe, a salad, or even ocean water are all mixtures.

• Pure Substances: Elements like gold, and compounds like water.
• Mixtures: Can be homogeneous (uniform composition) like saltwater or heterogeneous (not uniform) like a salad.

Understanding the difference between pure substances and mixtures helps in separating and identifying substances in chemistry.

Chemical Compounds

Think of chemical compounds as a recipe. Just like a cake recipe requires specific amounts of ingredients, compounds are made when elements combine in fixed ratios.
For example, in water (H₂O), always two hydrogen atoms bond with one oxygen atom.

This fixed arrangement is key to what we call a compound. It gives the compound its unique chemical and physical properties.

• Definite Proportions: Compounds always have the same proportion of elements, like H₂O for water or CO₂ for carbon dioxide.
• Characteristic Properties: Result from the specific combination of elements. Water is liquid at room temperature due to hydrogen bonding.

Compounds differ from mixtures because these properties are not just a mix, but a complete new set from the original elements.

Atoms and Molecules

Atoms are the fundamental building blocks of matter. Think of them as tiny Lego pieces that connect to form larger structures.
Each atom is unique, depending on its number of protons, electrons, and neutrons.

When atoms bond together, they create molecules. So, molecules are like clusters of Lego structures interconnected with each other.

• Atoms: Smallest unit of an element, cannot be divided further in chemical terms.
• Molecules: Consist of two or more atoms bonded together, can be of the same element (like O₂) or different ones (like H₂O).

Understanding atoms and molecules helps explain the nature of substances and the changes they can undergo in chemical reactions.