Problem 5 - 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 or gold chloride

Step-by-Step Solution

Answer

(a) Na: element, NaCl: compound; (b) sugar: compound, carbon: element; (c) gold: element, gold chloride: compound.

Step 1: Define an Element and a Compound

An **element** is a pure chemical substance consisting of one type of atom and is listed in the periodic table. **Compounds** are substances formed when two or more different types of atoms chemically bond together.

Step 2: Analyze Pair (a): Na or NaCl

- **Na** (Sodium) is an element because it consists of only one type of atom. - **NaCl** (Sodium chloride) is a compound because it consists of two different types of atoms: sodium (Na) and chlorine (Cl).

Step 3: Analyze Pair (b): Sugar or Carbon

- **Sugar** is a compound because it is made up of carbon, hydrogen, and oxygen atoms chemically bonded together (e.g., C₁₂H₂₂O₁₁ for table sugar). - **Carbon** is an element because it consists of only one type of atom.

Step 4: Analyze Pair (c): Gold or Gold Chloride

- **Gold** is an element because it consists of only one type of atom. - **Gold chloride** is a compound because it is made from gold (Au) and chlorine (Cl) atoms bonded together.

Key Concepts

Chemical Substances

Chemical substances are materials with a definite chemical composition. They can often be seen in forms such as elements or compounds.
Elements contain only one type of atom and can be found on the periodic table.
Examples include hydrogen, gold, and oxygen.

• Each element has its own unique properties based on its atomic structure.
• All atoms of an element have the same number of protons.

Compounds, on the other hand, are substances that form when two or more different types of atoms bond together.
This bonding results in a substance with unique characteristics and properties different from the individual atoms.

• Compounds require a fixed proportion by mass of the combining elements.
• They can be broken down into simpler substances through chemical reactions.

Recognizing and classifying chemical substances into elements and compounds helps us understand their compositions and how they might react in chemical processes.

Types of Atoms

Atoms are the smallest units of matter that retain the properties of an element.
Each atom is made up of three main parts: protons, neutrons, and electrons.
Elements have distinct types of atoms based on the number of protons in their nuclei.

• The number of protons, also known as the atomic number, determines the identity of the element.
• Atoms with the same number of protons but different numbers of neutrons are called isotopes.

Compounds involve different types of atoms coming together. When elements form compounds, their atoms participate in a specific type of chemical bonding. This results in a structure where the atoms are held in an arrangement that gives compounds their unique properties. Knowing about the types of atoms helps us visualize how compounds form and behave.

Chemical Bonding

Chemical bonding is the process where atoms combine to form compounds through attractive forces.
These bonds involve the change in electron configurations that lead to new formations.

• The most common types of chemical bonds include ionic bonds, covalent bonds, and metallic bonds.

Ionic bonds occur when atoms transfer electrons from one to another, creating ions. These ions then attract each other due to their opposite charges. For instance, in sodium chloride (NaCl), sodium (Na) donates an electron to chlorine (Cl), forming a stable compound.
Covalent bonds happen when atoms share electron pairs to achieve stability. For example, in a molecule of water (H₂O), each hydrogen atom shares electrons with the oxygen atom.
Understanding chemical bonding is crucial as it reveals how substances interact, form, and transform into different materials.