Electron configuration

—The lowest orbit level is called the ground state —As the electrons absorb more quantum energy, they get more excited and can jump to a higher orbit or energy level —There are different principal energy levels each with their own sublevels —Typically the principal levels correspond to the row number (except the transition elements) —The sublevels include s, p, d, and f.

What do quantum numbers mean?

—Principal Quantum number – tells you the primary energy shell where the electrons are found (includes all the sublevels) —Sublevel – tells you where the electrons are by the orbitals that are found in the sublevel. The “s, p, d, f” —Orbitals – the individual electron clouds that are found based on the probability (s, px,y,z, dxz, yz, xy, x2-y2, z2, f (has 7) —Each px, py and pz are individual orbitals Sublevel organization —As you see below, the sublevels (s, p, d, f) are all found in different sections. —The energy level (distance away from the nucleus) increases from s < p < d < f. So the f sublevel has the highest energy or the greatest distance from the nucleus. config               —








Each orbital holds a maximum of 2 electrons. —“s” orbital holds – 2 electrons —Each px, py, pz orbital holds – 2 electrons —But recall… calculating the maximum number of electrons is 2(n^2). —The energy level 2 (n=2) will give you 8 electrons… how? Or from where? Which orbitals? —2 electrons in the s orbital, 6 in the p orbital.

Electron configuration

—The electron configuration of an atom assigns a number to each electron. —The number includes the principal energy level of the electron, the name of the orbital and the number of electrons in that orbital. oxygen —






The electron configuration shows that

  • there are 2 electrons in the s-orbital of the first energy level (1s^2)
  • 2 electrons in the s-orbital of the second energy level (2s^2)
  • And 4 electrons in the p-orbital of the second energy level (2p^4).

—The orbitals are always written as lower case letters and the number of electrons is always written as superscripts. Figuring out Electron configuration —3 Principles must be followed –

  1. Aufbau
  2. Pauli Exclusion Rule
  3. Hund’s Rule

—Aufbau – German for “build up”, the principle was proposed by Neils Bohr. Electrons are added starting at the lowest energy level and build up to the higher levels. —The “1s” orbital is filled first, and then 2s and then 2p and so forth. *Look at the periodic table above* —Notice 4s orbital has a lower energy than 3d orbital so the 4s is filled before the 3d orbital.

—Pauli Exclusion Principle – Only a maximum of two electrons can occupy an orbital if they have opposite spins. pauli —





Hunds Rule – Proposed that as the electrons fill up the orbitals, they tend to maximize unpaired electrons in filling all the orbitals before completely filling one. —In other words, before filling the first p-orbital with two electrons, an electron is placed into the px orbital, then another electron into the py then pz before filling the px orbital. hund






A great tool to use to figure out the order of the orbitals and energy levels is the diagram below. Start by creating a column of 1s orbitals, and then beside the 2s, start your column of p orbitals, and then go down to the 3rd energy level for the d orbital etc… Draw your arrow diagonally down for your order! memory_aid_e_config