Atoms, Elements and Compounds - Atomic Structure and the Periodic Table

Defining the Proton Number/Atomic Number

The proton number, also known as the atomic number, is a fundamental property of an element. It defines the element and is equal to the number of protons found in the nucleus of an atom of that element.

Each element has a unique proton number. For example:

• Hydrogen (H) has a proton number of 1.
• Helium (He) has a proton number of 2.
• Carbon (C) has a proton number of 6.

The number of protons in an atom's nucleus is a defining characteristic and remains constant for an element. Changing the number of protons transforms an atom into a different element.

Key Concepts

• Proton: A subatomic particle with a positive electrical charge located in the nucleus of an atom.
• Neutron: A subatomic particle with no electrical charge (neutral) located in the nucleus of an atom.
• Electron: A subatomic particle with a negative electrical charge that orbits the nucleus.
• Nucleus: The central part of an atom, containing protons and neutrons.

Table: Examples of Elements and their Proton Numbers

Element	Symbol	Proton Number (Atomic Number)	Number of Neutrons (approximate)
Hydrogen	H	1	0
Helium	He	2	0
Lithium	Li	3	3
Carbon	C	6	6
Oxygen	O	8	8
Sodium	Na	11	12

Understanding the proton number is crucial for identifying elements and understanding their chemical properties. It forms the basis for the organization of the elements in the Periodic Table.