Electron configurations
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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.

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Electron Configurations

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Electron configurations

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 configurations1

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 configurations2

s

p

1

2

3

4

5

6

7

d (n-1)

6

7

f (n-2)

Electron Configurations


Electron configurations3

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 1s22s2 or [He]2s2.


Electron configurations4

s

p

1

2

3

4

5

6

7

d (n-1)

6

7

f (n-2)

Electron Configurations

  • C: 1s2 2s2 2p2 or [He] 2s2 2p2

  • Ne:1s2 2s2 2p6 or [He] 2s2 2p6

  • S: 1s2 2s2 2p6 3s2 3p4 or [Ne]3s2 3p4


Aufbau principle

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 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

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).

WRONG

RIGHT


Increasing energy

7p

6d

5f

7s

6p

5d

6s

4f

5p

4d

5s

4p

3d

4s

3p

3s

2p

2s

1s

Increasing energy


The noble gases

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

  • Helium1s2 [He]

  • Neon1s22s22p6 [Ne]

  • Argon1s22s22p63s23p6 [Ar]

  • Krypton1s22s22p63s23p63d104s24p6 [Kr]


Representative elements

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 elements1

Representative Elements

  • For any representative element, the group number equals the number of electrons in the outermost energy level (valence electrons)

  • Potassium1s22s22p63s23p64s1

  • Carbon, silicon, and germanium, in Group 4, have four electrons in the outermost energy level

  • Carbon1s22s22p2

  • Silicon1s22s22p63s23p2

  • Germanium1s22s22p63s23p63d104s24p2


Transition metals

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

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

Write the electronic configurations for the following elements

  • O

  • Na

  • Ar

  • Fe

  • Ca

  • Ce

1s22s22p4 or [He]2s22p4

1s22s22p63s1 or [Ne]3s1

1s22s22p63s23p6 or [Ne]3s23p6

1s22s22p63s23p63d64s2 or [Ar]3d64s2

1s22s22p63s23p64s2 or [Ar]4s2

1s22s22p63s23p63d104s24p64d105s25p64f15d16s2 or [Xe]4f15d16s2


Half full and full subshells

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] 4s13d10 rather than [Ar] 4s23d9

  • Cr exception: [Ar]4s13d5 rather than [Ar]4s23d4


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