What is the shell model? The shell model of the atom describes the arrangement of electrons around the nucleus of an atom in terms of energy levels or shells.

The 13 electrons in an aluminum atom are arranged in three energy levels of 2.8.3

The nuclear model of the atom states an atom is composed of a positively charge nucleus which is orbited by negatively charged electrons.

The shell model of the atom descibes how the electrons are arranged around the nucleus.

Three basics points will help you understand the arrangement of electrons around the nucleus of an atom.

1. The Atomic Number (number of protons) = The number of electrons in an atom.
2. The maximium number of electrons in the outer shell is eight
3. The maximum number of electrons in the inner shells is 2n2where n = the shell number

 Shell number, n 1 2 3 4 5 Maximum number of electrons in shell, 2n2 2 8 18 32 50

The Atomic Number of an element can be found from any Periodic table.

For example the Atomic number of the element bromine is 35. Bromine therefore has 35 protons and 35 electrons. The electron configuration of bromine is 2.8.18.7 which means there are 2 electrons in the first shell, 8 electrons in the second shell, 18 electrons in the third shell and 7 electrons in the fourth shell. The total number of electrons is 35.