Isotopes
Using atomic symbols
The number of protons and neutrons found in the nucleus of an atom. and The number of protons in the nucleus of an atom. Also called the proton number. are two important pieces of information about an The smallest part of an element that can exist..
An atom can be represented using the symbol notation:
\(_{Z}^{A}\textrm{X}\)
Where:
- A is the mass number
- Z is the atomic number
- X is the symbol of the A substance made of one type of atom only.
For example, chlorine (Cl) can be shown as:
This symbol shows that chlorine has 35 particles in the The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. The plural of nucleus is nuclei. (Subatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1. and Uncharged subatomic particle, with a mass of 1 relative to a proton. The relative charge of a neutron is 0.), 17 of which are protons. It also tells us that chlorine has 18 neutrons (35 - 17) and, as the number of electrons and protons are equal in a neutral atom, chlorine also has 17 Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons..
Atoms and isotopes
An element's atomic number defines it. An element with 17 protons will always be chlorine.
However an element's mass number can vary, which means that it can have different numbers of neutrons. So chlorine has a mass number of 35, which means it has 18 neutrons, but 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 three isotopes: \(_{6}^{12}\textrm{C}\), \(_{6}^{13}\textrm{C}\) and \(_{6}^{14}\textrm{C}\). They all contain six protons but six, seven and eight neutrons respectively.
\(_{7}^{14}\textrm{N}\) and \(_{6}^{14}\textrm{N}\) are not isotopes because they are not the same element. They have the same mass number but if the number of protons is different, they are different elements.
Example
How many protons does \(_{6}^{14}\textrm{C}\) contain?
The atomic number is 6 so \(_{6}^{14}\textrm{C}\) contains six protons.
Question
How many neutrons does \(_{6}^{14}\textrm{C}\) contain?
Number of neutrons = mass number - atomic number = 14 - 6 = 8 neutrons.