Atomic theory: explained in a simple way

The atoms are formed by an electrons cortex and a nucleus, formed by neutrons and protons that are stuck by the strong nuclear force. Electrons are found around the nucleus in a cloud of probability, it is much easier to visualize it if we remember that the electrons are not exactly particles but quanta and therefore in certain situations behave like stationary waves trapped in an atom and therefore each electron is Located in a different quantum state.

Image source: [1]

(Standing wave)

Pauli's exclusion principle prevents the fermions (particles with a natural half-spin) from having the same quantum state, which in the case of the electrons of the atomic core is described by the four quantum numbers: energy (n) , Angular momentum (l), magnetic moment (m) and spin (s) each with an integer value (1, 2, 3, ...). For each set of quantum numbers nlm we will have one type of electronic orbital and for each nlm we will have two electrons, each with the spin value, which is intrinsic but not its sign (+ 1/2, -1/2)

Image source: [2]

(Different types of orbitals, each corresponding to a set of numbers n, l and m)

More details here the link: [3]

Here two explanatory videos:

Video credit: Smart Learning for All

Video credit: TED-Ed