To outline the key features of the periodic table, atomic structure and chemical bonding.
Atomic Structure and Periodicity
In modern chemistry and physics it is agreed that the atom is made up of 3 key components: electrons, protons and neutrons. On the periodic table the position of an atom is decided by the number of protons and neutrons in the nucleus of the atom.
The proton, electron and neutron all have different characteristic regarding mass and charge these are as follows:
Particle | Relative Mass | Relative Charge |
Proton | 1 | +1 |
Neutron | 1 | ±0 |
Electron | 1/2000 | -1 |
Most of the atom is empty space, 99.9% to be exact. The 0.1% that is made up of the ...view middle of the document...
In each atom there is a different electronic structure of each atom. Depending on the atom depends on the number of shells and the number of electrons in the outer shell depends on the number of electrons in the atom.
A theory proposed by Niels Bohr stated about electron shells and this is still used today. He also stated that electron shells can hold a different number of electrons. This was that in shell 1, it held 2 electrons, in shell 2, 8 electrons and in shell 3, a further 8 electrons.
Here are a few examples of electron shell configurations:
Element | Atomic Number | Electrons |
| | N=1 | N=3 | N=3 |
Hydrogen | 1 | 1 | | |
Lithium | 3 | 2 | 1 | |
Oxygen | 8 | 2 | 6 | |
Fluorine | 9 | 2 | 7 | |
Phosphorus | 15 | 2 | 8 | 5 |
Potassium | 18 | 2 | 8 | 8 |
These electron shells are represented though dot and cross diagrams
Sub-shells are used in a more advanced idea of the shell diagram. As electrons will have an opposite spin as to repel each other.
There are 4 different categories of sub-shells:
Sub-Shell | Electrons |
SPDF | 261014 |
* The first shell (n=1) is made up of an S sub-shell only
* The second shell (n=2) is made up of S and P sub-shells
* The third shell (n=3) is made up of S, P and D sub-shells
* The fourth shell (n=4) is made up of S, P, D and F sub-shells
The first four principles quantum shells with their sub-shells are shown below:
Shell | N= | Sub-shell | Electrons |
1st | 1 | 1s | 2 | 2 |
2nd | 2 | 2s, 2p | 2+6 | 8 |
3rd | 3 | 3s, 3p, 3d | 2+6+10 | 18 |
4th | 4 | 4s, 4p, 4d, 4f | 2+6+10+14 | 32 |
Each sub-shell is made up of 1 or more orbitals – each orbital is represented by an individual square. Each orbital can hold up to 2 electrons (an electron pair)
When deciding which sub-shell electrons will need to follow two rules:
1) Electrons will occupy the sub-shell with the lowest possible energy levels first.
2) Electrons occupy orbitals of equal energy SINGLY before occupying pairs (Hunds’ Rule)
Electron configuration can be represented by using notations such as:
1s2, 2s2, 2p6, etc.
Number of electrons in the orbital
Number of electrons in the orbital
For each sub shell the notation shows different features:
Notations are different for each individual element, some are as follows:
Hydrogen | 1s1 |
Carbon | 1s2, 2s2, 2p2 |
Nitrogen | 1s2, 2s2, 2p3 |
Oxygen | 1s2, 2s2, 2p4 |
Sodium | 1s2, 2s2, 2p6, 3s1 |
Magnesium | 1s2, 2s2, 2p6, 3s2 |
Chlorine | 1s2, 2s2, 2p6, 3s2, 3p5 |
In the period table elements can be identified by their position and electron configuration, with the most important factor being the highest energy electron in the configuration.
Chlorine has an electron configuration of 1s2, 2s2, 2p6, 3s2, 3p5; this means that the highest energy electron is in the 3p sub-shell, it additionally identifies the element being in...