Problem 11 - Chemistry and Chemical Reactivity

Question

In each of the following pairs, decide which is an element and which is a compound. (a) Na or NaCl (b) sugar or carbon (c) gold

Step-by-Step Solution

Answer

(a) Na is an element; NaCl is a compound. (b) Carbon is an element; sugar is a compound. (c) Gold is an element.

Step 1: Identify Element in (a)

An element is a pure chemical substance consisting of one type of atom. Sodium (\( \text{Na} \)) is an element because it is made up entirely of sodium atoms.

Step 2: Identify Compound in (a)

A compound is a chemical substance composed of two or more different elements chemically bonded together. Sodium chloride (\( \text{NaCl} \)) is a compound because it is made of sodium and chlorine atoms bonded together.

Step 3: Identify Compound in (b)

A compound consists of two or more different elements chemically combined. Sugar, which could be sucrose (\( \text{C}_{12}\text{H}_{22}\text{O}_{11} \)), is a compound because it contains carbon, hydrogen, and oxygen atoms bonded together.

Step 4: Identify Element in (b)

An element consists of only one type of atom. Carbon (\( \text{C} \)) is an element because it is composed entirely of carbon atoms.

Step 5: Determine Element in (c)

Since gold is only one substance made up of gold atoms, it is an element. Gold's chemical symbol is \( \text{Au} \).

Key Concepts

Chemical Substances

Chemical substances are materials with a distinct chemical composition. They are characterized by the type and arrangement of atoms within them. These substances can either be elements or compounds. Chemical substances are recognized by their unique properties, which include taste, smell, color, and boiling point. Additionally, they have distinct chemical behaviors that help in identification.

• Elements consist of only one type of atom.
• Compounds consist of two or more different atoms bonded together.

Understanding the composition of a chemical substance is key to predicting its behavior and reactions with other substances.

Atoms

Atoms are the basic units of matter, forming the foundation of chemical substances. They consist of a nucleus containing protons and neutrons, surrounded by electrons. Atoms are characterized by the number of protons they contain, which is known as the atomic number. This determines the element to which the atom belongs.

• Protons are positively charged.
• Neutrons have no charge and add mass to the atom.
• Electrons are negatively charged, orbiting the nucleus.

These components interact to define the unique properties of each atom, and by extension, the properties of the element or compound they form.

Chemical Bonds

Chemical bonds are the forces that hold atoms together in chemical substances. They result from the interaction of electrons of adjacent atoms. There are several types of chemical bonds, each with different characteristics:

• Ionic Bonds: Formed when electrons are transferred from one atom to another, creating charged particles called ions.
• Covalent Bonds: Formed when atoms share pairs of electrons to achieve stability.
• Metallic Bonds: Occur between metal atoms sharing a "sea of electrons" which allows for conductivity and malleability.

Understanding chemical bonds is essential to knowing how elements combine to form stable compounds.

Pure Substances

Pure substances are materials composed entirely of one type of particle, either elements or compounds, with uniform properties throughout. These substances differ from mixtures, which contain two or more different particles mixed physically but not chemically bonded.

• Pure elements consist of only one type of atom, such as gold ( \( \text{Au} \)).
• Pure compounds consist of molecules made of different types of atoms, like water ( \( \text{H}_{2} \text{O} \)).

By understanding the differentiation between pure substances and mixtures, students can better approach the classification and identification of chemical substances in reactions.