chemistry unit 1 .3

Shells, sub-shells, and orbitals

Shells are principal energy levels, sub-shells are divisions within shells (s, p, d), and orbitals are regions within sub-shells where electrons are likely to be found.

Principal quantum number (n)

It indicates the energy level of an electron in an atom and can take positive integer values (1, 2, 3, ...).

s sub-shell

Has 1 orbital and can hold a maximum of 2 electrons.

p sub-shell

Has 3 orbitals and can hold a maximum of 6 electrons.

d sub-shell

Has 5 orbitals and can hold a maximum of 10 electrons.

Order of increasing energy of sub-shells

The order is 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p.

Electronic configuration of atoms

Representation of the distribution of electrons among the orbitals of an atom.

Energy of electrons and inter-electron repulsion

Higher energy levels are occupied first; electrons repel each other, affecting the arrangement.

Full electronic configuration for Fe

1s2 2s2 2p6 3s2 3p6 3d6 4s2.

Shorthand electronic configuration for Fe

[Ar] 3d6 4s2.

Electron in boxes notation

Visual representation of electron configuration showing unpaired and paired electrons in orbitals.

Shape of s orbital

Spherical.

Shape of p orbital

Dumbbell-shaped.

Free radical

A species that has one or more unpaired electrons, making it highly reactive.