Elements

Definition

Elements are pure substances consisting of only one type of atom. They cannot be broken down into simpler substances by chemical means.

5 Must Know Facts For Your Next Test

1. Elements are listed in the periodic table and each has a unique atomic number.
2. The atomic number of an element is determined by the number of protons in its nucleus.
3. Elements are the building blocks for all matter, including biological molecules.
4. There are 118 known elements, with about 20-25 considered essential for life.
5. Carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur (CHNOPS) are key elements in biological systems.

Review Questions

• What determines the identity of an element?
• How many types of atoms make up an element?
• Which six elements are most important in biological molecules?

Related terms

Atom: The smallest unit of an element that retains its chemical properties.

Molecule: A group of two or more atoms bonded together.

Periodic Table: A tabular arrangement of all known elements organized by their atomic number and chemical properties.