The Quantum Model
From the Double-Slit experiment, we learned that matter has a wave-particle duality, or can act as both. We learned that matter has a wavelength. Erwin Schrodinger used this to create a “wave function”, which described electrons, The quantum model says that elections exist as waves in regions of probability, which gave a probability field for electrons, meaning we know what region an electron is in.
Each energy level in an atom has a certain amount of orbitals, or areas where an electron can be. The s orbital (1st) has only 1 orbital, creating a simple probability field. The p orbital (2nd) has 3 orbitals creating 3 possible probability fields. The d orbital has 5 orbitals, creating 5 possible probability fields.
A quantum number is a way of telling us the energy level, shape and position of the orbital, and spin of the electrons of any element. An electron configuration is a representation of the quantum number. It is written with a combination of energy levels and orbitals. Each period has a new energy level. H and He are in the first energy level, Li, Be, B, C, N, O, F, and Ne are in the second, etc.
Valence electrons are also very important for electron configuration. Valence electrons are the remaining electrons in the outermost energy level. Elements in the first family (H, Li, Na) have one valence electron and elements in the second family (Be, Mg, Ca) have 2 valence electrons. Then, elements in the 13th family (B, Al, Ga) have 3 valence electrons, elements in the 14th family (C, Si, Ge) have 4 valence electrons, and so on until the 18th family.
The s orbital is always included, as it shows at least one valence electron. There can only be two electrons in an orbital, and they become paired electrons. Because of this, only two electrons are allowed in the s orbital. After the s orbital is the p orbital, which can hold a total of 3 orbitals or 6 electrons. The p orbital is always included when there are at least 3 valence electrons, which are in elements in the families 3-18. The d orbital is included for any of the elements in families 3-12. When the p orbital is full, the electrons can be found in the d orbital. However, the d orbital is always one energy level lower than the other 2. Note: for this, helium is in the 2nd family rather than the 18th.
The best way to learn what electron configuration is by looking at examples. Hydrogen is written in electron configuration as 1s¹ (said as 1 s 1), showing us that it is in the first energy level and only has one electron in the s orbital while having no electrons in the p or d orbitals.
Lithium has a configuration of 1s² 2s¹, which means the 1st energy level s orbital is full, and the 2nd energy level s only has 1 electron in it.
Nitrogen has a configuration of 1s² 2s² 2p³. This means that the 1st and 2nd energy levels’ s orbitals are full, and the second energy level p has 3 electrons.
Scandium, Sc, has an electron configuration of 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 4p⁶ 3d¹. We know that the first, second, and third energy levels are full, but the fourth has a full s and p orbital. Then, the d orbital only has one electron in it (remember that the d orbital’s energy level is reduced by 1).
This pattern repeats until the lanthanides and actinides in the periodic table (the two rows under the main block), where the f orbital shows up. Its energy level is reduced by 2 and goes from 1-14.
With n as energy level, the s block uses the equation ns¹⁻², the p block uses np¹⁻⁶, the d block uses (n - 1)d¹⁻¹⁰, and the f block uses (n - 2)f¹⁻¹⁴.
Core notation is a way of shortening electron configuration. Instead of writing the entire notation for elements, you can write [noble gas] with the noble gas (18th family) below it, and bypass all the energy levels that are in that particular noble gas’s notation. For example, sulfur can be written as 1s² 2s² 2p⁶ 3s² 3p⁴. However, using core notation, it can simply be written as [Ne] 3s² 3p⁴.
