Electronic structure
An A set of numbers to show how the electrons in an atom are arranged in shells, or energy levels. is the way in which Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons. are arranged in an The smallest part of an element that can exist..
Electrons in shells
Electrons in atoms occupy energy levels, also called electron shells, outside 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.. Different shells can hold different maximum numbers of electrons. The electrons in an atom occupy the lowest available energy level first. This is the shell nearest the nucleus. When this shell is full the electrons begin to occupy the next energy level.
Below is a table showing the maximum number of electrons an element can have for each of its energy level shells. The information shown is for elements with The number of protons in the nucleus of an atom. Also called the proton number. 1 to 20:
| Shell | Maximum |
| First | 2 |
| Second | 8 |
| Third | 8 |
| Shell | First |
|---|---|
| Maximum | 2 |
| Shell | Second |
|---|---|
| Maximum | 8 |
| Shell | Third |
|---|---|
| Maximum | 8 |
Predicting an electronic structure
The electronic structure of an atom can be predicted from its atomic number. For example, the atomic number of sodium is 11. Sodium atoms have 11 Subatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1. and so 11 electrons:
- two electrons occupy the first shell
- eight electrons occupy the second shell
- one electron occupies the third shell
This electronic structure can be written as 2,8,1 (each comma, or dot, separates one shell from the next). This electronic structure can also be shown as a diagram. In these diagrams:
- each shell is shown as a circle
- each electron is shown as a dot or a cross
Electronic structures and the periodic table
The electronic structure of an A substance made of one type of atom only. is linked to its position on the A tabular representation of all known elements in order based on atomic number, eg all the noble gases are found on the right of the periodic table..
| Electronic structure feature | Link to the periodic table |
| Number of shells | Period number |
| Number of electrons in outermost shell | Group number |
| Total number of electrons in all shells | Atomic number |
| Electronic structure feature | Number of shells |
|---|---|
| Link to the periodic table | Period number |
| Electronic structure feature | Number of electrons in outermost shell |
|---|---|
| Link to the periodic table | Group number |
| Electronic structure feature | Total number of electrons in all shells |
|---|---|
| Link to the periodic table | Atomic number |
The electronic structure of sodium (2,8,1) shows that sodium, Na:
- is in period 3
- is in group 1
- has an atomic number of (2 + 8 + 1) = 11