Electron Configurations Of the three major subatomic particles, the electron plays the most significant role in determining the physical and chemical properties of an element. The arrangement of elements in the periodic table depends on these properties. Thus, there should be some relationship between the electron configurations of the elements and their placement in the table.

Electron Configurations The orbital names s, p, d, and f stand for names given to groups of lines in the spectra of the alkali metals. These line groups are called sharp, principal, diffuse, and fundamental.

Electron Configurations d (n-1) p s 6767 f (n-2)

Electron Configurations The electron configuration of an atom denotes the distribution of electrons among available shells. The standard notation lists the subshell symbols, one after another. The number of electrons contained in each subshell is stated explicitly. For example, the electron configuration of beryllium, with an atomic (and electron) number of 4, is 1s 2 2s 2 or [He]2s 2.

Electron Configurations C: 1s 2 2s 2 2p 2 or [He] 2s 2 2p 2 Ne:1s 2 2s 2 2p 6 or [He] 2s 2 2p 6 S: 1s 2 2s 2 2p 6 3s 2 3p 4 or [Ne]3s 2 3p d (n-1) p s 6767 f (n-2)

Aufbau Principle Electrons fill orbitals starting at the lowest available energy states before filling higher states (e.g. 1s before 2s). The number of electrons that can occupy each orbital is limited by the Pauli Exclusion Principle (each orbital can hold two electrons with opposite spins).

The rules of the Aufbau Principle are: “The Lazy Tenant Rule” 1.Electrons are placed in the lowest energetically available subshell. 2. An orbital can hold at most 2 electrons. 3.If two or more energetically equivalent orbitals are available (e.g., p, d etc.) then electrons should be spread out before they are paired up (Hund's rule).

Hund's Rule “The Empty Bus Seat Rule” If multiple orbitals of the same energy are available, Hund's Rule says that unoccupied orbitals will be filled before occupied orbitals are reused (by electrons having different spins). WRONGRIGHT

Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f

The Noble Gases These are the elements in which the outermost s and p subshells are filled. The noble gases have full outer shells; notice that these elements have filled outermost s and p sublevels Helium1s 2 [He] Neon1s 2 2s 2 2p 6 [Ne] Argon1s 2 2s 2 2p 6 3s 2 3p 6 [Ar] Krypton 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 [Kr]

Representative Elements In these elements, the outermost s or p sublevel is only partially filled. There are three groups of representative elements: Group 1 alkali metals Group 2 alkaline earth metals Group 7 halogens

Representative Elements For any representative element, the group number equals the number of electrons in the outermost energy level (valence electrons) Potassium1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 Carbon, silicon, and germanium, in Group 4, have four electrons in the outermost energy level Carbon1s 2 2s 2 2p 2 Silicon1s 2 2s 2 2p 6 3s 2 3p 2 Germanium1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 2

Transition Metals These are metallic elements in which the outermost s sublevel and nearby d sublevel contain electrons. The transition elements are characterized by addition of electrons to the d orbitals

Inner Transition Metals These are the metallic elements in which the outermost s sublevel and nearby f sublevel generally contain electrons

Write the electronic configurations for the following elements O Na Ar Fe Ca Ce 1s 2 2s 2 2p 4 or [He]2s 2 2p 4 1s 2 2s 2 2p 6 3s 1 or [Ne]3s 1 1s 2 2s 2 2p 6 3s 2 3p 6 or [Ne]3s 2 3p 6 1s 2 2s 2 2p 6 3s 2 3p 6 3d 6 4s 2 or [Ar]3d 6 4s 2 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 or [Ar]4s 2 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 5s 2 5p 6 4f 1 5d 1 6s 2 or [Xe]4f 1 5d 1 6s 2

Half-Full and Full Subshells full subshell: fully-filled shells are lower in energy than partially-filled shells (i.e. Noble Gases) half-filled subshells: lower in energy than partially-filled subshells Cu exception: [Ar] 4s 1 3d 10 rather than [Ar] 4s 2 3d 9 Cr exception: [Ar]4s 1 3d 5 rather than [Ar]4s 2 3d 4