The atom and isotopes
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Explainer Video
Summary
The atom and isotopes
In a nutshell
This summary will review the structure of an atom and its components. Different types of atoms from the same element will also be reviewed, with worked examples.
Atomic structure
Atoms have a radius of around and are made up of different components, responsible for the properties of the elements they form.
The atom
The atom is the smallest part of a chemical element that can exist. It is made from subatomic particles. This can be seen below.
part of the atom | location and contents |
| Nucleus |
|
| Shells |
|
Subatomic particles
The different subatomic particles have different relative masses and charges. This is shown in the table below.
Subatomic particle | Relative Mass | Charge |
| Proton | | |
| Neutron | | |
| Electron | | |
Note: The overall charge on an atom is zero because the number of protons equals the number of electrons and the charges cancel out.
Atomic and mass numbers
These numbers are used to describe an atom.
Nuclear symbol
The nuclear symbol can tell you a lot about the element.
Example
- Atomic number - the amount of protons in the atom (the smaller number).
- Mass number - the total amount of protons and neutrons in the atom (the larger number).
Note: You can calculate the number of neutrons in an atom by working out the difference between the two numbers (mass number subtract atomic number). The number of electrons is the same as protons (unless it is an ion).
Isotopes
Definition
These are different forms of the same element, with the same number of protons but different number of neutrons. This means that isotopes have the same atomic number but different mass numbers.
Example
and are a common pair of isotopes.
Isotope | COMPOSITION |
| | Six protons, six electrons, six neutrons |
| | Six protons, six electrons, seven neutrons |
Relative atomic mass
When referring to isotopes, we use a value called relative atomic mass () instead of mass number since it takes into account the different abundances of different isotopes that make up an element.
FAQs - Frequently Asked Questions
What is an isotope?
An isotope is an atom of an element with the same number of protons but different number of neutrons.
Why is the charge of an atom neutral?
Atoms are neutral because they have the same number of protons and electrons and the opposing charges cancel out.
What are the names of three subatomic particles in an atom, and where are they located?
Protons are located in the nucleus. Neutrons are located in the nucleus. Electrons are located on the shells.