Isotopes
An A substance made of one type of atom only. The number of protons in the nucleus of an atom. Also called the proton number. defines it. An element with 17 Subatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1. will always be chlorine.
However an element's The number of protons and neutrons found in the nucleus of an atom. can vary, which means that it can have different numbers of Uncharged subatomic particle, with a mass of 1 relative to a proton. The relative charge of a neutron is 0.. So although chlorine usually 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 Atoms of an element with the same number of protons and electrons but different numbers of neutrons..
There are three isotopes of hydrogen: hydrogen, deuterium (hydrogen-2) and tritium (hydrogen-3):
Carbon has 3 isotopes: 126C, 136C and 146C. They all contain six protons, but six, seven and eight neutrons respectively.
147N and 146C are not isotopes because although they have the same mass number, they are not the same element. If the number of protons changes, then it is a different element.
Example
How many protons does 146C contain?
The atomic number is 6 so 146C contains six protons.
Question
How many neutrons does 146C contain?
Number of neutrons = mass number - atomic number = 14 - 6 = 8 neutrons.