3.5 Atomic Structure and the Periodic Table

electron shielding

• Inner electrons repel outer electrons → reduce the effective nuclear charge felt by the outermost electron.

electron configuration

the location and number of electrons in the electron energy levels of an atom

aufbau principle

the theory that an atom is "built up" by the addition of electrons, which fill orbitals starting at the lowest available energy orbital before filling higher energy orbitals

e.g. 1s before 2s

noble gas configuration

done by using the nearest noble gas preceding the element. This is then noted in brackets; and electron config., is continued from there.

 

So, sodium would be: [Ne]3s¹

Where [Ne] represents the electron config., of neon; 1s²2s²2p⁶

valence electron

an electron in the outermost principle quantum level of an atom

transition metal

an element whose highest-energy electrons are in d orbitals

transition metals and multiple ions

• Transition metals can form multiple positive ions (variable oxidation states).

• This is due to the availability of both s and d electrons in the outer shells.