Never trust an atom, they make up everything! The structure of an atom is very easy to understand once it has been explained.
Atoms are made of 3 sub-atomic particles which are; protons and neutrons (in the nucleus) and electrons in shells orbiting it.
Protons and neutrons give an atom its mass. Electrons have a minute mass (1/2000th) so we say it has no mass.
Protons carry a +1 charge and electrons carry a -1 charge so overall an atom has no charge. It can gain a charge from losing or gaining an electron, this creates an ion.
'A neutron walks into a bar; he asks the bartender, "How much for a beer?" The bartender looks at him, and says "For you, no charge."'
At GCSE we learn that in the 1st shell there can be up to 2 electrons, it then fills the 2nd shell and then the 3rd which can contain up to 8 each.
The top number is called the atomic number, it tells us how many protons and electrons are in the atom. The bottom number is known as the mass number, it tells us the mass, this is the number of protons and neutrons.
Orbitals
At alevel we learn a more detailed explanation about the atom and its shells, these shells are now called energy levels.
On each energy level there are subshells. Within these subshells there are orbitals. Each orbital can contain 2 electrons.
S subshell; 1 orbital
P subshell: 3 orbitals
D subshell: 5 orbitals
The 1st energy level contains one subshell, this is an s-subshell. Within this subshell there is only one orbital, this one orbital can contain up to 2 electrons, thus the first energy level contains up to 2 electrons.
The 2nd energy level contains an s and a p subshell. The p subshell has 3 orbitals which can contain 2 electrons each. This 6 plus the 2 in the s subshell equals 8.
The 3rd energy level contains an s, p and d subshell. Within the d subshell there are 5 orbitals. The total number of electrons is 18.
S subshells are spherical and P subshells are like dumbbells:
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