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Atomic Number - IGCSE Chemistry Definition

Reviewed by: Alexandra Brennan

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What is atomic number?

In IGCSE chemistry, the atomic number is the number of protons in the nucleus of an atom and is unique to each element. It determines the element’s identity and position in the Periodic Table.

For example, hydrogen has an atomic number of 1, meaning it has one proton, while oxygen has an atomic number of 8, meaning it has eight protons. In a neutral atom, the atomic number also equals the number of electrons, which balance the positive charge of the protons. The atomic number is essential in understanding chemical properties and reactions in IGCSE Chemistry.

Diagram explaining element notation: Mass number (A) is protons plus neutrons, atomic number (Z) is protons, and X is the chemical symbol.
The atomic number indicates the number of protons

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Alexandra Brennan

Reviewer: Alexandra Brennan

Expertise: Chemistry

Alex studied Biochemistry at Newcastle University before embarking upon a career in teaching. With nearly 10 years of teaching experience, Alex has had several roles including Chemistry/Science Teacher, Head of Science and Examiner for AQA and Edexcel. Alex’s passion for creating engaging content that enables students to succeed in exams drove her to pursue a career outside of the classroom at SME.

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