Electron Configuration CHEMISTRY 11 MS. MCGRATH

The Uncertainty Principle It is inherently impossible for us to know simultaneously both the exact momentum of electrons and their exact location in space ie We anticipate that it is not possible to determine exactly where an electron is located at a specific time

Electron Configuration Recall The Bohr model assumes the electrons are in a circular orbit of some particular radius around the nucleus In the quantum-mechanical model, the electrons’ location cannot be described so simply In the quantum-mechanical model, we speak of the probability that the electron will be in a certain region of space at a given instant

Quantum Numbers There are three principle quantum numbers: 1. principle quantum number, n 2. secondary quantum number, l (n - 1) 3. magnetic quantum number, m l

Quantum Numbers 1. principle quantum number, n n can have a range of 1 to infinity n = 1, 2, 3,...∞ as n increases the orbital becomes larger and the electrons spend more time away from the nucleus an increase in n also means that the electron has a higher energy and is less tightly bound to the nucleus

Quantum Numbers 2. secondary quantum number, l l can have values from 0 to n -1 defines the shape of the orbital the values of l for a particular orbital is generally designated by s, p, d, f which corresponds to l values of 0, 1, 2, 3 values of l: letter used: s p d f

Quantum Numbers 3. magnetic quantum number, m l m l can have values between l and -l describes the orientation of the orbital in space

Electron Configuration Recall that at this point, our construction the atom is the following: comprised of electrons, neutrons, and protons neutrons and protons are found in the nucleus electrons are present in orbits (energy levels or shells) each shell contains orbitals (spaces where electrons are likely to be found)

Electron Configuration Orbitals (s, p, d, f) s Orbital The first orbit (or shell) only has an “s” orbital This orbital is spherical and can hold 2 electrons This orbital is in every energy level

Electron Configuration Orbitals (s, p, d, f) p Orbital This orbital is said to be dumbbell shaped It has 3 sub orbitals, each of these sub orbitals can hold 2 electrons (so the p orbital can hold a total of 6 electrons) The p orbital occurs in energy levels 2 and above

Electron Configuration Orbitals (s, p, d, f) d Orbital The d orbital is composed of 5 sub orbitals, each of these sub orbitals can hold 2 electrons (so the d orbital can hold a total of 10 electrons) The d orbital occurs in energy levels 3 and above

Electron Configuration Orbitals (s, p, d, f) f Orbital The f orbital is composed of 7 sub orbitals, each of these sub orbitals can hold 2 electrons (so the f orbital can hold a total of 14 electrons) The f orbital occurs in energy levels 4 and above

Electron Configuration It is important to know the order in which the electrons are placed:

Electron Configuration

Electron Configuration

Notice when we get to period 4 (the 4 th row) we fill the 4s orbital then the 3rd orbital The f orbitals (in the Lanthanides and Actinides) can be inserted after the 6 th and 7 th s orbitals.

Electron Configuration There is one more principle we must understand before communicating electron configuration - Aufbau Principle - this principle can be summarized in the following statements and is true for nearly all atoms. Electrons will occupy the lower energy level orbital first Electrons will fill each sub orbital with one electron before filling any suborbital with two electrons (Hund’s Rule)

Electron Configuration There are three methods to express electron arrangement: 1.Energy Level Diagrams 2.SPDF Notation or Standard Notation 3.Noble Gas Notation

Energy Level Diagrams

Class Activity draw out the energy level diagrams for the following elements: HydrogenBarium HeliumLanthanum CarbonLutetium OxygenHafnium Xenon Cesium

spdf Notation Physicists and chemists use a standard notation to indicate the electron configurations of atoms. The notation consists of a sequence of atomic orbital labels specifying the orbit, they type of orbital within that orbit, then an superscript indicating the number of electrons present in that orbital.

spdf Notation Examples 1.hydrogen has one electron which is in the s orbital of the first shell, so its configuration is written 1s 1 2.lithium has three electrons in total its configuration is written 1s 2 2s 1 3.phosphorus has fifteen electrons in total, its configuration is written 1s 2 2s 2 2p 6 3s 2 3p 3

spdf Notation Class Activity write out the spdf notation for the following elements: HydrogenBarium HeliumLanthanum CarbonLutetium OxygenHafnium Xenon Cesium

Noble Gas Notation This is an abbreviated notation All but the last few subshells are identical to those of one or another of the noble gases so we can make use of this.

Noble Gas Notation Example Phosphorus (which has fifteen electrons) differs from neon (1s 2 2s 2 2p 6 ) only by the presence of a third shell. The electron configuration of neon is pulled out, and phosphorus is written as follows: Phosphorus: [Ne] 3s 2 3p 3

Noble Gas Notation Class Activity write out the Noble Gas Notation for the following elements: Hydrogen Helium Carbon Oxygen Xenon Cesium