Atoms are made up of protons, neutrons and electrons. The position of protons and neutrons within an atom is pretty simple to define – they’re in the nucleus at the centre of the atom.
It’s not so simple, however, to state the position of an electron within an atom – we can’t be certain of their positions (or where they are travelling – Heisenberg’s Uncertainty Principle).
Electrons occupy spaces called orbitals. An orbital is a region around the nucleus of an atom which is occupied by up to two electrons. Essentially, electrons can be found anywhere within this space almost 100% of the time (but technically there is a small chance they could be anywhere in the universe).
IMPORTANT NOTE: Electrons do not orbit the nucleus in the same way Earth orbits the Sun, they occupy an orbital.
There are four different types of orbital called s, p, d and f, each with a different shape.
Types of Orbitals
s Orbitals
s orbitals are spherical in shape and symmetrical. Each shell in an atom contains one s orbital.
As the principle quantum number increases, the region with the greatest probability of finding an electron gets further away from the nucleus.
p Orbitals
p orbitals have a 3D dumb bell shape. Only shells from n=2 and upwards contain p-orbitals and each one has 3, denoted as: px, py and pz each at right angles to one another.
They have direction, unlike s orbitals. As there are 3 p orbitals in a shell this means that each shell from n=2 and above can contain up to 6 p electrons.
d Orbitals
d orbitals are more complex than s and p orbitals. Shells from n=3 and upwards contain 5 d orbitals defined as dxy, dyz, dzx, dx2-y2 and dz2 (depending on the level you’re studying at you probably don’t need to remember these).
Unlike p orbitals, not all of the d orbitals within a shell are the same shape. As each d orbital can hold up to 2 electrons, each shell (from n=3 and above) can contain up to 10 d electrons.
f Orbitals
f orbitals are even more complex than d orbitals and each shell from n=4 and upwards contains 7 f orbitals. As with d orbitals, not all f orbitals are the same shape. They can be denoted as follows (again, you probably don’t need to know these):
fy(3x2-y2), fz(x2-y2),fyz2, fz3, fxz2, fxyz and fx(x2-3y2).
Each shell (from n=4 and above) can contain up to 14 f electrons.
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