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Difference Between Atomic Mass and Atomic Number

Difference Between Atomic Mass and Atomic Number; atomic number is the number of protons in the nucleus of an atom, Atomic mass is the sum of the masses of protons and neutrons

Praveen Kushwah10 Jun, 2025

Difference Between Atomic Mass and Atomic Number : Have you ever wondered why different elements have different weights and characteristics? The answer lies in two important concepts in chemistry - atomic mass and atomic number. These two quantities are related, but not the same, as different isotopes of the same element can have different atomic masses but the same atomic number.

In this article, we will explore the difference between atomic mass and atomic number, and how they are used in the NEET syllabus for Physics and Chemistry.

Difference Between Atomic Mass and Atomic Number

The atomic number is the number of protons in the nucleus of an atom. It determines the identity and the chemical properties of an element. For example, hydrogen has an atomic number of 1, helium has an atomic number of 2, and carbon has an atomic number of 6. Atomic mass is the sum of the masses of protons and neutrons in the nucleus of an atom. It measures the weight of an atom in atomic mass units (AMU). For example, hydrogen has an atomic mass of 1.0079 amu, helium has an atomic mass of 4.0026 amu, and carbon has an atomic mass of 12.011 amu.

Difference Between Atomic Mass and Atomic Number Overview

The NEET Syllabus covers topics from classes 11 and 12 of the CBSE and other state boards and is revised by the National Medical Commission (NMC) and the National Testing Agency (NTA) to reflect the latest requirements of the medical profession. Understanding the difference between atomic mass and atomic number is essential for NEET aspirants, as it helps them to solve problems related to the structure and properties of atoms, molecules, and compounds.

Difference Between Atomic Mass and Atomic Number
Parameter	Atomic Mass	Atomic Number
Definition	The total mass of an atom, including protons and neutrons.	The number of protons in the nucleus of an atom.
Symbol	Usually represented by "A."	Represented by "Z."
Unit	Unified Atomic Mass Unit (u) or atomic mass unit (AMU).	Dimensionless (no unit).
Composition	Includes protons and neutrons in the nucleus.	Only counts the number of protons in the nucleus.
Relationship	Atomic mass = Protons + Neutrons	No direct relationship with the mass of an atom.
Variation in Isotopes	Different isotopes of an element have different atomic masses.	The same element always has the same atomic number.
Mass Defect	Reflects the difference between the mass of an atom and the sum of its protons and neutrons.	Not applicable to atomic numbers.
Measurement	Determined through techniques like mass spectrometry.	Determined through experimental techniques, such as X-ray crystallography or spectroscopy.
Importance in Periodic Table	Used to calculate the average atomic mass of an element based on its isotopic abundance.	Determines the position of an element in the periodic table.
Examples	Carbon-12 has an atomic mass of 12 u.	Carbon-12 has an atomic number of 6 (Z=6).

What is an Atomic Number?

The atomic number is the number of protons in the nucleus of an atom. It is represented by the letter Z and determines the identity and the chemical properties of an element. For example, hydrogen has an atomic number of 1, which means it has one proton in its nucleus. Helium has an atomic number of 2, which means it has two protons in its nucleus.

What is an Atomic mass?

Atomic mass is the sum of the masses of protons and neutrons in the nucleus of an atom. It is represented by the letter A and measures the weight of an atom in atomic mass units (amu). For example, hydrogen has an atomic mass of 1.0079 amu, which means the mass of one proton and zero neutrons in its nucleus. Helium has an atomic mass of 4.0026 amu, which means the mass of two protons and two neutrons in its nucleus. If you are looking for the best NEET online coaching in India? then you should join PW NEET online coaching , the most affordable and comprehensive program for NEET aspirants. With PW NEET Online Coaching, you will get access to live lectures, study materials, mock tests, and doubt-solving sessions from the best faculty in the country. You will also get to learn from the renowned Physics Wallah, who has helped millions of students achieve their dreams. Don’t miss this opportunity to prepare for NEET with PW NEET Online Coaching. Enroll now and get ready to crack NEET with confidence.

NEET Exam Important Links
NEET Chemistry Syllabus	NEET Chemistry Important Questions with Answers
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Difference Between Oxidation and Reduction	Difference Between SN1 and SN2
Difference Between Thermoplastic and Thermosetting Plastics	Difference Between Molecule and Compound

Difference Between Atomic Mass and Atomic Number FAQs

What is the relationship between atomic number and atomic mass?

The atomic number (Z) of an atom is the number of protons in its nucleus, while the atomic mass (A) is the sum of protons and neutrons. The relationship is expressed by the equation: Atomic Mass = Protons + Neutrons. Each element has a unique atomic number, and isotopes of an element have different atomic masses due to variations in the number of neutrons.

What is different mass and same atomic number?

Atoms with the same atomic number (Z), indicating they belong to the same element, may have different masses if they are isotopes. Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons, resulting in distinct atomic masses.

What is atomic number and mass number explain with example?

For example, consider carbon. Carbon-12 has an atomic number of 6 (six protons) and a mass number of 12 (six protons + six neutrons). Another isotope, Carbon-14, also has an atomic number of 6 but a mass number of 14 (six protons + eight neutrons). Both isotopes are carbon because they have the same atomic number, but they differ in mass due to a distinct number of neutrons.

What is an atom atomic mass and atomic number Class 9?

In class 9, students learn that an atom is the basic building block of matter, consisting of a nucleus (protons and neutrons) and electrons orbiting the nucleus. Atomic mass is the total mass of an atom, and atomic number is the number of protons. The periodic table helps relate atomic number to elements and provides atomic masses for various isotopes.

What are atomic masses and atomic numbers of elements?

Atomic masses and atomic numbers vary for different elements. The atomic number uniquely identifies an element, while the atomic mass is the average mass of its isotopes weighted by their abundance. Both pieces of information are crucial in understanding the structure and properties of elements, and they are readily available in the periodic table.

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In this article, we will explore the difference between atomic mass and atomic number, and how they are used in the NEET syllabus for Physics and Chemistry.

Difference Between Atomic Mass and Atomic Number

Difference Between Atomic Mass and Atomic Number Overview

Difference Between Atomic Mass and Atomic Number
Parameter	Atomic Mass	Atomic Number
Definition	The total mass of an atom, including protons and neutrons.	The number of protons in the nucleus of an atom.
Symbol	Usually represented by "A."	Represented by "Z."
Unit	Unified Atomic Mass Unit (u) or atomic mass unit (AMU).	Dimensionless (no unit).
Composition	Includes protons and neutrons in the nucleus.	Only counts the number of protons in the nucleus.
Relationship	Atomic mass = Protons + Neutrons	No direct relationship with the mass of an atom.
Variation in Isotopes	Different isotopes of an element have different atomic masses.	The same element always has the same atomic number.
Mass Defect	Reflects the difference between the mass of an atom and the sum of its protons and neutrons.	Not applicable to atomic numbers.
Measurement	Determined through techniques like mass spectrometry.	Determined through experimental techniques, such as X-ray crystallography or spectroscopy.
Importance in Periodic Table	Used to calculate the average atomic mass of an element based on its isotopic abundance.	Determines the position of an element in the periodic table.
Examples	Carbon-12 has an atomic mass of 12 u.	Carbon-12 has an atomic number of 6 (Z=6).

What is an Atomic Number?

What is an Atomic mass?

NEET Exam Important Links
NEET Chemistry Syllabus	NEET Chemistry Important Questions with Answers
NEET Chemistry Chapter wise Weightage	NEET Chemistry MCQs
NEET Chemistry Notes	NEET Chemistry Formulas

Chemistry Difference Between Articles
Difference Between Ideal Gas and Real Gas	Difference Between Vapor and Gas
Difference Between Physical and Chemical Change	Difference Between Vaporization and Evaporation
Difference Between Atom and Molecule	Difference Between CNG and LPG
Difference Between Sigma and Pi Bond	Difference Between Fats and Oils
Difference Between Baking Soda and Baking Powder	Difference Between Glucose and Fructose
Differences Between Evaporation and Boiling	Difference Between Elements and Atoms
Difference Between Element and Compound	Difference Between Enantiomers and Diastereomers
Difference Between Petrol and Diesel Engine	Difference Between Hard Water and Soft Water
Difference Between Oxidation and Reduction	Difference Between SN1 and SN2
Difference Between Thermoplastic and Thermosetting Plastics	Difference Between Molecule and Compound