Atomic Electron Configuration: Hund's Rule, Valence Electrons, and Orbitals, Study notes of Chemistry

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Hund’s Rule, Orbital Diagrams, and

Valence Electrons

The Big Questions

• Now that we know how electrons are

arranged into atoms, how are they arranged

into sublevels and orbitals?

• How can we communicate the arrangement

of atoms in orbitals?

• What are valence electrons and why are

they more important than other electrons?

Review

• Sublevels are made of orbitals.

• s -type sublevels are made of 1 orbital.

• p -type sublevels are made of 3 orbitals.

• d -type sublevels are made of 5 orbitals.

• f -type sublevels are made of 7 orbitals.

• Every orbital can hold up to 2 electrons.

Review

• In an atom, electrons fill the lowest

sublevels first (aufbau principle).

• Fill higher energy sublevels only when lower

ones are already filled.

• Order of filling is not as expected.

Hund’s Rule

• In a sublevel, every orbital gets one electron

before any orbital gets a pair.

• Example:

• e

   config. for carbon: 1s 

2 2s

2 2p

2

1s 2s 2p

orbitals sublevel

energy level

Hund’s Rule

• e

config. for oxygen: 1s

2

2s

2

2p

4

1s 2s 2p

orbitals sublevel

energy level

Orbital Diagrams

• Orbital diagram for hydrogen.

• e

config: 1s

1

1s

Orbital Diagrams

• Orbital diagram for helium.

• e

config: 1s

2

1s

Orbital Diagrams

• Orbital diagram for beryllium.

• e

config: 1s

2

2s

2

1s 2s

Orbital Diagrams

• Orbital diagram for boron.

• e

config: 1s

2

2s

2

2p

1

1s 2s 2p

Orbital Diagrams

• Orbital diagram for nitrogen.

• e

config: 1s

2

2s

2

2p

3

1s 2s 2p

Orbital Diagrams

• Orbital diagram for oxygen.

• e

config: 1s

2

2s

2

2p

4

1s 2s 2p

Orbital Diagrams

• Orbital diagram for neon.

• e

config: 1s

2

2s

2

2p

6

1s 2s 2p

Orbital Diagrams

• Orbital diagram for sodium.

• e

config: 1s

2

2s

2

2p

6

3s

1

1s 2s 2p 3s