All matter is made up of atoms. Atoms are so tiny that they need to be magnified millions of times in order to be seen. However atoms are themselves made of subatomic particles. In this lesson we will learn about the inside of atoms and the role of protons and neutrons in an atom.
What are atoms made of?
Atoms are made up of protons, neutrons and electrons. Protons and neutrons make up the nucleus of an atom. Whereas electrons move rapidly around the nucleus in regions called electron shells.
Summary of subatomic particles:-
Subatomic particles | Symbol | Relative Charge | Relative Mass |
Inside the nucleus: Protons | p | +1 | 1 |
Inside the nucleus: Neutrons | n | 0 | 1 |
Outside the nucleus: Electrons | e | -1 | 1/1840 |
The number of electrons in an atom is the same as the number of protons. Therefore,
the negative charges cancel out the positive charges ; hence an atom is electrically neutral
Proton Number:
The proton number is also called the atomic number. It refers to the number of protons in an atom. It is represented by the symbol of Z . Since atoms are electrically neutral, the proton number can also tell us the number of electrons in an atom. For example, if an atom has 7 proton number then it means it has 7 protons and 7 electrons.
Do atoms of different elements have the same proton number?
Each element has a unique proton number. If the oxygen atom has a proton number of 8, then only oxygen atom will have the proton number of 8.
Nucleon Number:
The nucleon number of an atom is the total number of protons and neutrons in the atom. The nucleon number of an atom is represented by the symbol A . It is also called the mass number. This is because the mass of an atom depends on the number of protons and neutrons in the atom's nucleus. The mass of electrons is said to be negligible.
Nucleon Number (A) = number of protons + number of neutrons
Representing the proton and nucleon number:
The value of proton number is always lesser than the nucleon number
A
X
Z
For example, a sodium atom has 12 neutrons and 11 protons. Thus, sodium can be represented by:
23
Na
11
Sometimes it can also be written with only its nucleon number: sodium-23 or 23
Na
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