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Atomic Number vs. Mass Number: What's the Difference?

Edited by Huma Saeed || By Sara Rehman || Published on January 22, 2024
Atomic number is the count of protons in an atom's nucleus, while mass number is the total of protons and neutrons.

Key Differences

The atomic number, found on the periodic table, identifies the element by counting the protons in the nucleus. The mass number represents the sum of protons and neutrons, indicating the atom's mass.
Sara Rehman
Jan 22, 2024
Elements are arranged by atomic number, reflecting the number of protons, which defines the element's identity. Mass number, however, can vary in isotopes of the same element due to differing neutron counts.
Sara Rehman
Jan 22, 2024
Atomic number determines the chemical properties of an element, as it defines electron configuration. The mass number affects the atomic mass but doesn't significantly alter chemical properties.
Sara Rehman
Jan 22, 2024
A change in atomic number means a change in the element itself, while a change in mass number represents different isotopes.
Aimie Carlson
Jan 22, 2024
Atomic number is always a whole number and unique for each element. Mass number also is a whole number but can vary within the same element.
Harlon Moss
Jan 22, 2024
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Comparison Chart

Definition

Count of protons in nucleus
Total of protons and neutrons
Sara Rehman
Jan 22, 2024

Variation in Isotopes

Constant for each element
Varies in different isotopes
Huma Saeed
Jan 22, 2024

Determines

Element identity
Atomic mass
Sara Rehman
Jan 22, 2024

Effect on Chemical Properties

Defines chemical properties
Does not alter chemical properties
Aimie Carlson
Jan 22, 2024

Representation on Periodic Table

Directly listed
Not directly listed
Aimie Carlson
Jan 22, 2024
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Atomic Number and Mass Number Definitions

Atomic Number

Atomic number determines the element's chemical properties.
Carbon's atomic number of 6 defines its unique properties.
Sara Rehman
Dec 23, 2023

Mass Number

Mass number varies in different isotopes of the same element.
Uranium-238 has a mass number of 238.
Sara Rehman
Dec 23, 2023

Atomic Number

Atomic number is the number of protons in an atom's nucleus.
The atomic number of hydrogen is 1.
Sara Rehman
Dec 23, 2023

Mass Number

Mass number is not listed on the periodic table.
The mass number of isotopes must be calculated or referenced.
Harlon Moss
Dec 23, 2023

Atomic Number

Atomic number equals the number of electrons in a neutral atom.
Neon, with an atomic number of 10, has 10 electrons.
Aimie Carlson
Dec 23, 2023

Mass Number

Mass number is always a whole number.
An iron atom with 26 protons and 30 neutrons has a mass number of 56.
Harlon Moss
Dec 23, 2023

Atomic Number

It identifies the position of an element on the periodic table.
Helium has an atomic number of 2, placing it second on the table.
Sara Rehman
Dec 23, 2023

Mass Number

It indicates the total mass of the nucleus.
A carbon atom with mass number 12 has 6 protons and 6 neutrons.
Huma Saeed
Dec 23, 2023

Atomic Number

The atomic number is unique to each element.
Oxygen's atomic number, 8, is exclusive to it.
Janet White
Dec 23, 2023

Mass Number

Mass number is the sum of protons and neutrons in an atom.
The mass number of helium-4 is 4.
Sara Rehman
Dec 23, 2023

FAQs

What is mass number?

The mass number is the total number of protons and neutrons in an atom.
Huma Saeed
Jan 22, 2024

Can the atomic number change for an element?

No, the atomic number is constant for each element.
Sara Rehman
Jan 22, 2024

What is atomic number?

The atomic number is the count of protons in an atom's nucleus.
Sara Rehman
Jan 22, 2024

How is mass number calculated?

By adding the number of protons and neutrons in an atom.
Janet White
Jan 22, 2024

Can two elements have the same atomic number?

No, each element has a unique atomic number.
Janet White
Jan 22, 2024

Are atomic number and mass number the same?

No, they represent different properties of an atom.
Sara Rehman
Jan 22, 2024

Can mass number be a decimal?

No, mass number is always a whole number.
Harlon Moss
Jan 22, 2024

Is atomic number shown on the periodic table?

Yes, atomic number is directly listed on the periodic table.
Aimie Carlson
Jan 22, 2024

Does the mass number change in isotopes?

Yes, different isotopes of the same element have different mass numbers.
Aimie Carlson
Jan 22, 2024

Can isotopes of an element have the same mass number?

No, isotopes differ in mass number due to varying neutron counts.
Sara Rehman
Jan 22, 2024

Why is atomic number important in chemistry?

It identifies elements and determines their chemical behavior.
Janet White
Jan 22, 2024

Can atomic number be zero?

No, atomic number starts from 1 (hydrogen) upwards.
Janet White
Jan 22, 2024

Does mass number vary in chemical reactions?

No, chemical reactions involve electrons and don't change mass number.
Janet White
Jan 22, 2024

What determines an element's position on the periodic table?

The atomic number determines an element's position.
Sara Rehman
Jan 22, 2024

Can an element have multiple mass numbers?

Yes, due to the existence of different isotopes.
Harlon Moss
Jan 22, 2024

What happens to the atomic number during radioactive decay?

It can change, as radioactive decay may involve proton emission or capture.
Aimie Carlson
Jan 22, 2024

Does mass number affect an element's chemical properties?

No, mass number does not significantly alter chemical properties.
Sara Rehman
Jan 22, 2024

Is the mass number equal to the atomic mass?

Not exactly, atomic mass is the average mass considering all isotopes.
Aimie Carlson
Jan 22, 2024

Is the atomic number equal to the number of electrons?

Yes, in a neutral atom, the atomic number equals the electron count.
Janet White
Jan 22, 2024

Does changing the number of neutrons change the atomic number?

No, changing neutrons affects the mass number, not the atomic number.
Harlon Moss
Jan 22, 2024
About Author
Written by
Sara Rehman
Sara Rehman is a seasoned writer and editor with extensive experience at Difference Wiki. Holding a Master's degree in Information Technology, she combines her academic prowess with her passion for writing to deliver insightful and well-researched content.
Edited by
Huma Saeed
Huma is a renowned researcher acclaimed for her innovative work in Difference Wiki. Her dedication has led to key breakthroughs, establishing her prominence in academia. Her contributions continually inspire and guide her field.

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