Sec 2 Quantum Chemistry- Atomic Structure/ Particles

Atomic Structure

As mentioned in the chemistry module, each electron shell has different energy levels. The quantum chemistry module will explore deeper in the structure of atoms, in terms of electron shells.

Each shell is actually divided further into various sub-shells. For the first shell, there is only 1 sub-shell; the second shell has 2 sub-shells; the third has 3, the forth as 4, etc. Each sub-shell is given a specific name: s, p, d, f, and g. (In theory, there are more as the are atoms with more than 5 electron shell; This is discussed in the Quantum-Quantum Chemistry module). Hence, the 1^st shell contains 1 s sub-shell; the seconds contains both s and p; third contains s, p and d, the forth contains s, p d and f, and so on. Each sub-shell is further divided into orbitals (Don’t confuse this with electron orbits, or shells). Each orbital can hold 2 electrons. Study the table below:

Sub-shell	Number of orbitals	Number of electron it can hold
s	1	2
p	3	6
d	5	10
f	7	14
g	9	18

Hence, since the first electron shell only has 1 s sub-shell, which only has 1 orbital, it can only hold 2 electrons.The electrons fill up each shell gradually by energy level. The electron configuration in spdf can be “calculated” using the number of electrons and the sub-shells it fit. Below (Or rather to the left) is a way of remembering the sub-shell energy levels:

 As seen, when the 1s orbital is filled, the 2s would then occupy the 3^rd and 4^th electron and so on. The electronic configuration of sulphur in spdf is shown below:

1s² 2s² 2p⁶ 3s² 3p⁴        OR

[Ne] 3s² 3p⁴

Each number before the letter shows the electron shell the orbital is on. The “power of” the letter is the number of electrons filled in the orbital. [Ne] is a short form for the electronic configuration of Neon: it is used to simplify the electronic configuration of elements with many electrons. Note that each unit of the configuration is arranged in increasing energy.

Particles

Alpha Particle	Helium-2 nucleus (Or 2 protons and 2 neutrons)
Beta Particle	One Electron