What Are the Relationships Between Electrons & Orbitals?

Electrons reside around the nucleus of atoms in orbitals analogous to the orbits of a planet around its star

Electrons and orbitals are fundamentally related and form the core of bonding theories in chemistry. According to Purdue University, the location of an electron can never be known exactly, but a region can be calculated where it is probable the electron will be found. Georgia State University points out that electron orbital studies begin with understanding the electron around a hydrogen atom and build in complexity as elements get larger and contain more electrons with more possible configurations. Florida State University adds that electron orbitals are commonly denoted with the letters s, p, d, f and numbers that correspond to their home atoms' horizontal row in the periodic table.

Electron Orbitals and the Heisenberg Uncertainty Principle

Werner Heisenberg formulated a fundamental theory of quantum mechanics that argues that the exact location of an electron around an atom can never be known precisely. This principle, the Heisenberg uncertainty principle, resulted in the formation of the idea of electron orbitals. These are regions in space around an atom's nucleus where electrons are likely to be found. These regions were split into shells depending on the size of the atom and then into orbitals within these shells of varying shapes. Orbitals are subdivided into lobes, each lobe by a single electron.

Electron Orbitals and the Pauli Exclusion Principle

These electron orbitals are occupied by electrons in a particular order: from the lowest energy orbital to the highest. The Pauli exclusion principle states that only two electrons can be present in a given orbital at a given time. Together a model can be formed that described the relative dispersal of electrons around the nucleus of any atom. Electrons fill the lowest numbered shell available and fill subsequently higher energy level shells and orbitals. Degenerate lobes -- those with the same letter and shell designation -- each fill with a single electron before electrons begin to pair.

Representations of Electron Orbitals and Fill Order

Increasing shell energy levels are designated by increasing numbers and orbitals by their place in a sequence of letters. Orbitals assigned the letter "s" are circular in shape with two hemispheric lobes and occupy the lowest energy level within their shell. The "p" orbitals are next with six total lobes jutting out on the x, y and z axis in the positive and negative directions. The "d" orbitals are next and feature 10 lobes spreading in all directions. Finally, there are the "f" orbitals with 14 total lobes. Every shell from period 1 onward has an "s" orbital, every shell from period 2 onward has a "p" orbital, each shell from period 4 on up features a "d" orbital and period 6 on up has an "f" orbital. All lower level energy shells are present in higher energy shells as well.

Electrons and Orbitals Beginning with Hydrogen

The most important energy shell in any atom is the highest numbered and is called the valence shell. The number of valence shell atoms and their orbital configurations are the heart of bonding and reactions in chemistry. Hydrogen atoms are the simplest -- they have one electron and are in the first row of the periodic table. They have one energy shell and one orbital, the 1s orbital. This means that hydrogen atoms have one valence electron and this explains why hydrogen is so reactive. In contrast, consider argon. Argon has 18 atoms and is on the third row of the periodic table, so its highest energy level is shell 3. Its electron orbitals are 1s, 2s, 2p, 3s, 3p and are filled in that order -- two electrons in each "s" and six in each "p" for a grand total of 18 electrons.

References

• Purdue University: What Is An Atomic Orbital?
• Georgia State University: Visualizing Electron Orbitals
• Florida State University: Atomic Orbitals