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Particles Inside An Atom: Protons, Neutrons and Electrons Guide As Well As Atomic Number And Mass

An atom consists of a dense small nucleus surrounded by electrons (negatively charged particles). Protons and neutrons are subatomic particles located inside the nucleus.

The charge of an electron is -1

The charge of a proton is +1

Neutron is neutral with no charge


Both a proton and a neutron have a mass of 1 amu (atomic mass unit) each, while electron is so light is its mass is approximately 0 amu. Therefore, most of the mass of the atom is concentration inside the nucleus.


Atomic Number is unique to every element. All of the atoms of the same element must have the same atomic number.

Atomic number is equal to the number of protons and can be easily found on the Periodic Table (lower right corner).


Mass number is equal to the number of protons + neutrons.

Atoms of the same element with different masses(different number of neutrons) are called isotopes. All isotopes of the same element have mostly identical chemical properties.


When writing an element symbol, the top number represents the mass number (protons + neutrons), while the bottom number represents the atomic number (protons).


Example, how much protons, neutrons and electrons?



Sulfur, as shown above, has 16 protons (atomic number is equal to the number of protons.

16 electrons (number of protons and electrons is equal for a neutral atom)

17 neutrons ( 33-16=17)


How to calculate the number of protons, neutrons and electrons inside an ion?

If the atom has a charge, it is called an ion. The only difference in calculation will be for the number of electrons! Electrons are negatively charged. -1 charge means one more electron than protons. -2 charge means two more electrons and so on. If the charge is positive, that means the atom lost electrons.

Let's take a look at an example:

How many protons and electrons are in:


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