Atoms are the building blocks of all matter. Every solid, liquid and gas is composed of these tiny particles. These atoms are said to be composed of tiny sub-atomic particles called protons, neutrons and electrons. The protons and neutrons are found in the nucleus surrounded by shells of moving electrons. Protons have a relative charge of +1, electrons have a relative charge of -1, while neutrons do not carry a charge. It is important to note that there is an equal number of protons and electrons and as a result the overall charge on an atom is 0. Both protons and neutrons both have a relative mass of 1 while electrons have a relative mass of 0. As a result, electrons do not contribute to the mass of an atom; they, however play a significant rule in bonding. Bonding is discussed in more detail later in these Wizznotes.
The structure of an atom is shown below:
As can be seen the protons and neutrons are in the center of the atom, while the electrons are found outside in shells surrounding the nucleus. Electrons are arranged in a particular manner in these shells and this arrangement is called the electron configuration. These shells can only hold a certain number of electrons. The first electron shell has a maximum capacity of 2 electrons. The second and third shells have a maximum capacity of 8 electrons and the 4th shell has a maximum capacity of 18. Each shell must be filled with electrons in order for electrons to be packed into the shell on the next level.
Atoms of the same type group together to form elements. There are many different kinds of elements and these are all listed in the period table