Question

Classify each of the following pure substances as an element or a compound: a. a silicon (Si) chip b. hydrogen peroxide \(\left(\mathrm{H}_{2} \mathrm{O}_{2}\right)\) c. oxygen \(\left(\mathrm{O}_{2}\right)\) d. rust \(\left(\mathrm{Fe}_{2} \mathrm{O}_{3}\right)\) e. methane \(\left(\mathrm{CH}_{4}\right)\) in natural gas

Short answer

a. element, b. compound, c. element, d. compound, e. compound

Step-by-step solution

- Determine the classification of silicon (Si)

A silicon chip is composed of pure silicon. Since silicon is a single type of atom found on the periodic table, it is classified as an element.

- Determine the classification of hydrogen peroxide \(\text{H}_{2}\text{O}_{2}\)

Hydrogen peroxide consists of two hydrogen atoms and two oxygen atoms chemically bonded. As it contains more than one type of atom, it is classified as a compound.

- Determine the classification of oxygen \(\text{O}_{2}\)

Oxygen in its diatomic form (\(\text{O}_{2}\)) consists of two oxygen atoms bonded together. Since it only contains one type of atom (oxygen), it is classified as an element.

- Determine the classification of rust \(\text{Fe}_{2}\text{O}_{3}\)

Rust is a chemical compound composed of two iron atoms and three oxygen atoms. As it contains more than one type of atom, it is classified as a compound.

- Determine the classification of methane \(\text{CH}_{4}\)

Methane consists of one carbon atom and four hydrogen atoms chemically bonded. Since it consists of more than one type of atom, it is classified as a compound.

Key concepts

elements

Elements are pure substances made up of only one kind of atom. For instance, silicon (Si) is an element. You'll find it on the periodic table, which lists all the elements by their atomic number. In our example, oxygen \(\text{O}_{2}\) is also an element even though it consists of two oxygen atoms bonded together. That's because it's just one kind of atom. Understanding what makes a substance an element is fundamental in chemistry.
Remember, elements are the building blocks of all matter.

compounds

Compounds are substances formed when two or more different types of atoms chemically bond together. Hydrogen peroxide \(\text{H}_{2}\text{O}_{2}\), rust \(\text{Fe}_{2}\text{O}_{3}\), and methane \(\text{CH}_{4}\) are all examples of compounds. Each compound has its own unique set of properties, different from the elements that form it. For instance, water is a compound consisting of hydrogen and oxygen, but its properties are very different from both hydrogen and oxygen gases. Identifying and understanding compounds is a key skill in chemistry.

periodic table

The periodic table is an organized chart of all known elements. Each element has a unique position and is represented by a symbol, like Si for silicon or O for oxygen. The table is arranged by increasing atomic number, typically from left to right and top to bottom. Elements in the same column (group) share similar chemical properties. This table is not just a list; it's a powerful tool that helps scientists predict the properties and behaviors of elements. Being familiar with the periodic table is crucial for anyone studying chemistry.

chemical bonding

Chemical bonding is the process where atoms combine to form compounds. There are different types of bonds, such as ionic, covalent, and metallic bonds. A covalent bond involves the sharing of electron pairs between atoms, like in hydrogen peroxide \(\text{H}_{2}\text{O}_{2}\). An ionic bond, on the other hand, involves the transfer of electrons from one atom to another, creating ions that attract each other. Understanding chemical bonding helps explain how compounds are formed and how they behave. It's a cornerstone concept in chemical reactions and compound formation.