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Number of Protons and Neutrons

Atom

"The Atom"

Number of Protons and Neutrons
This section provides details of the number of protons and neutrons in all of the elements in the Periodic Table.

Number of Protons and Neutrons - What is an Atom?
To understand the association between the number of Protons and Neutrons and an element we need to ask a basic question.

What is an atom? Everything that takes up space (called Matter) has weight, volume and mass.

Matter is made up of tiny building blocks called Atoms. Atoms are tiny at least 100 times smaller than the width of a human hair. The exact size of the atom changes, depending on the element.

Number of Protons and Neutrons - An Atom determines an Element
The purest type of atom is called an element. Atoms are composed of three kinds of smaller particles, called protons, neutrons and electrons. Protons and neutrons are made up of even smaller particles called quarks. The number of protons, the number of neutrons and the number of electrons an atom has determines what the element it is.

  • Atoms are composed of 3 kinds of small particles: protons, neutrons and electrons

  • Atoms must have equal numbers of protons and electrons

The nucleus is in the middle of the atom and contains protons and neutrons. These smaller particles - the protons, neutrons and electrons - all have different properties.

Number of Protons and Neutrons - What are Electrons?
A reminder of the definition before discovering how to calculate the numbers. Electrons are tiny, very light particles that have a negative electrical charge. Atoms must have equal numbers of protons and electrons.

Number of Protons and Neutrons - What are Protons?
Protons are much larger and heavier than electrons and have a positive charge. Atoms must have equal numbers of protons and electrons.

Number of Protons and Neutrons - What are Neutrons?
Neutrons are large and heavy like protons, however neutrons have no electrical charge.

Number of Protons and Neutrons - How to find the Atomic Number of an element
Every element has a unique Element Symbol and a unique Atomic Number which can be accessed via the Periodic Table with Atomic Mass.

  • Definition: The atomic number is the number of protons in the atom of an element.

The periodic Table is a really important tool to Chemistry students enabling them to recognise the names of elements from their Atomic number. The chemical elements of the periodic table are listed in order of atomic number. You can also refer to the bottom of this page to an at-a-glance table of all the elements and their atomic numbers in numerical order.

Number of Protons and Neutrons - How to find the Number of Protons - Examples
The atomic number is based on the number of protons in the atom of an element. (Note: Atoms must also have equal numbers of protons and electrons.) So, if we know the atomic number of an element then we also know how many protons in an element.

  • Example 1 - Numbers of Protons in Gold: The element Gold (Symbol Au) has the Atomic Number of 79. Any atom that contains exactly 79 protons in its nucleus is an atom of gold. The number of protons in atom of gold is therefore 79.

  • Example 2 - Numbers of Protons in Silver: The element Silver (Symbol Ag) has the Atomic Number of 47. Any atom that contains exactly 47 protons in its nucleus is an atom of silver. The number of protons in atom of silver is therefore 47.

  • Example 3 - Numbers of Protons in Neon: The element Neon (Symbol Ne) has the Atomic Number of 10. Any atom that contains exactly 10 protons in its nucleus is an atom of gold. The number of protons in atom of gold is therefore 10.

Adding or removing protons from the nucleus of an atom creates a different element. For example, removing one proton from an atom of Gold creates an atom of Platinum (Platinum has the Atomic number 78 therefore the number of protons =78.) Adding one proton from an atom of Gold creates an atom of Mercury (Mercury has the Atomic number 80 therefore the number of protons =80.). Refer to the table below and work out the number of protons in various elements.

Number of Protons and Neutrons - How to find the Atomic Mass number
Calculating the number of neutrons in an atom or element is a little more complicated. For this calculation you need to establish the atomic weight from which you will be able to establish the Atomic Mass Number. The atomic weight or mass is, basically, a measurement of the total number of particles in an atom's nucleus. The atomic mass number is established by rounding the atomic weight to the nearest whole number. The Periodic Table with Atomic Mass will give you the atomic weight, or atomic mass, of the elements.

Atomic Mass Number = Atomic Weight of Element, rounded to nearest whole number

So, if we know the number of protons and neutrons in an atom (element) we can determine the Atomic Mass Number

  • Example 1 - Atomic Mass of Gold: The element Gold (Symbol Au) has the Atomic Number of 79. The number of protons in atom of gold is therefore 79. Gold has the Atomic Mass weight of 196.97. Round to the nearest whole number. The atomic mass number of gold is therefore 197.

  • Example 2 - Atomic Mass of Silver: The element Silver (Symbol Ag) has the Atomic Number of 47. The number of protons in atom of silver is therefore 47. Silver has the Atomic Mass weight of 107.87. Round to the nearest whole number. The atomic mass number of silver is therefore 108.

  • Example 3 - Atomic Mass of Neon: The element Neon (Symbol Ne) has the Atomic Number of 10. The number of protons in atom of neon is therefore 10. Neon has the Atomic Mass weight of 20.18. Round to the nearest whole number. The atomic mass number of neon is therefore 20.

Number of Protons and Neutrons - How to find the Number of Neutrons
We can identify the number of neutrons in an atom or element by using the information we already have.  To find the numbers of neutrons, subtract the atomic mass number from the atomic number.

Number of Neutrons = Mass Number - Atomic Number

  • Example 1 - The element Gold (Symbol Au). The atomic mass number of gold is 197 and has the Atomic Number of 79. The Numbers of Neutrons in Gold is 197 - 79 =  118

  • Example 2 - The element Silver (Symbol Ag). Number of Neutrons in Silver: The atomic mass no. of silver is 108 and has the Atomic Number of 47. The Numbers of Neutrons in Neon is 108 - 47 = 61

  • Example 3 - The element Neon (Symbol Ne). The atomic mass number of neon is 20 and has the Atomic no. of 10.  Numbers of Neutrons in Neon is 20 - 10 = 10

Adding or removing protons from the nucleus of an atom creates a different element but adding or removing neutrons from the nucleus of an atom does not create a different element.

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