A nucleus can be represented using the symbol notation:
For example, chlorine (Cl) can be shown as:
Cl is the chemical symbol for chlorine
A chlorine nucleus will contain:
The chlorine atom will also have 17 electrons, as an atom is neutral.
An element's atomic number defines it.
An element with 17 protons will always be chlorine.
However an element's mass numbers can vary, which means that it can have different numbers of neutrons.
So although chlorine has a mass number of 35 which means it has 18 neutrons, it can also have a mass number of 37, which means it has 20 neutrons.
The different types of chlorine are called isotopes of chlorine.
There are three isotopes of hydrogen: hydrogen, deuterium (hydrogen-2) and tritium (hydrogen-3):
Carbon has three isotopes: , and . They all contain six protons, but six, seven and eight neutrons respectively.
and are not isotopes.
They have the same mass number, A, but different atomic number, Z, and different chemical symbol - they are not the same element.
If the number of protons changes, then it is a different element.
How many protons does contain?
The atomic number is 6 so contains six protons.
How many neutrons does contain?
Number of neutrons = mass number - atomic number = 14 - 6 = 8 neutrons.
Write down the number of particles in the following nuclei:
There are 30 protons and 34 neutrons.
There are 92 protons and 146 neutrons.
There is 1 proton and 2 neutrons.